Too much of a good thing? Teamwork in medical education

Teams and the promotion of teamwork for both faculty and for students can be key components of integrated curriculum and 'flipped classroom' active learning approaches for medical education. The benefits of teams and teamwork are presented to faculty and students, sometimes via indoctrination, but the costs of the team approach, balanced against the purported benefits, are typically not discussed. This unbalanced presentation creates the need for a statement of a contrarian view. I posit that among the problems of teams and teamwork in education are diminishment of individual initiative and individual responsibility, lowering standards to the least common denominator, creating excess obligations with respect toward weaker team members, negative effects on academic freedom, inconsistency with respect to how faculty and students are evaluated, and giving students a somewhat false view of their accountability as a medical professional. Possible ideological considerations and attitudes toward individualism with respect to teams need to be understood as well.

Immunotherapy and Cannabis: A Harmful Drug Interaction or Reefer Madness?

A retrospective (N = 140) and a prospective (N = 102) observational Israeli study by Bar-Sela and colleagues about cannabis potentially adversely impacting the response to immunotherapy have together been cited 202 times, including by clinical practice guidelines. There have also been concerns on PubPeer outlining irregularities and unverifiable information in their statistics and numerous errors in calculating percentages. This reanalysis attempted to verify the data analysis while including non-parametric statistics. The corrected prospective report contained 22 p-values, but only one (4.5%) could be verified despite the authors being transparent about the N and statistics employed. Cannabis users were significantly (p < 0.0025) younger than non-users, but this was not reported in the retrospective report. There were also errors in percentage calculations (e.g., 13/34 reported as 22.0% instead of 38.2%). Overall, these observational investigations, and especially the prospective, appear to contain gross inaccuracies which could impact the statistical decisions (i.e., significant findings reported as non-significant or vice-versa). Although it is mechanistically plausible that cannabis could have immunosuppressive effects which inhibit the response to immunotherapy, these two reports should be viewed cautiously. Larger prospective studies of this purported drug interaction that account for potential confounds (e.g., greater nicotine smoking among cannabis users) may be warranted.

Evaluating the medical curriculum: Bias, problems, solutions

Medical school curriculums have increasingly shifted to an integrated curriculum and have been replacing lecture with 'flipped classroom' approaches. Analyses of the benefits of the integrated curriculum and flipped classroom model typically report enhanced student performance. However, the question is whether institutional self-evaluation of curricular success is biased to demonstrate success that may not objectively exist and/or whether such biased data are presented during Liaison Committee on Medical Education (LCME) site visits. An objective determination of curricular effectiveness requires an absence of bias and of efforts to put an institutional 'thumb on the scale' to obtain desired results. In addition, bias may exist in the rationale for implementing these curricular changes in the first place; these can include, for example, with respect to career advancement as well as ideological motivation. Thus, in this paper I examine potential problems with institutional bias with evaluation of curriculum and how to overcome these.

Hypothesis: functional age and onset of autosomal dominant genetic prion disease

Autosomal dominant diseases typically have an age-related onset. Here, I focus on genetic prion disease (gPrD), caused by various mutations in the PRNP gene. While gPrD typically occurs at or after middle age, there can be considerable variability in the specific age of onset. This variability can occur among patients with the same PRNP mutation; in some cases, these differences occur not only between families but even within the same family. It is not known why gPrD onset is typically delayed for decades when the causative mutation is present from birth. Mouse models of gPrD manifest disease; however, unlike human gPrD, which typically takes decades to manifest, mouse models exhibit disease within months. Therefore, the time to onset of prion disease is proportional to species lifespan; however, it is not known why this is the case. I hypothesize that the initiation of gPrD is strongly influenced by the process of aging; therefore, disease onset is related to proportional functional age (e.g., mice vs. humans). I propose approaches to test this hypothesis and discuss its significance with respect to delaying prion disease through suppression of aging.

Oncogenic and Receptor-Mediated Wnt Signaling Influence the Sensitivity of Colonic Cells to Butyrate

Deregulated Wnt signaling is responsible for most cases of colorectal cancer (CRC). Dietary fiber is protective against CRC and this activity is likely mediated by butyrate, a breakdown product of dietary fiber that hyperactivates Wnt signaling, repressing CRC proliferation and inducing apoptosis. Receptor-mediated Wnt signaling and oncogenic Wnt signaling, which is typically initiated by mutation in more downstream elements of the pathway, activate non-overlapping patterns of gene expression. Receptor-mediated signaling is associated with a poor prognosis for CRC while oncogenic signaling is associated with a relatively good prognosis. We have compared the expression of genes differentially expressed in receptor-mediated vs. oncogenic Wnt signaling to microarray data generated in our laboratory. Most importantly we evaluated these gene expression patterns comparing the early stage colon microadenoma line LT97 with the metastatic CRC cell line SW620. LT97 cells exhibit a gene expression pattern more strongly associated with that observed with oncogenic Wnt signaling, while SW620 cells exhibit a gene expression pattern moderately associated with that observed with receptor-mediated Wnt signaling. Given that SW620 cells are more advanced and malignant compared to LT97 cells, these findings are generally consistent with the better prognosis observed with tumors exhibiting a more oncogenic Wnt gene expression pattern. Importantly, LT97 cells are more sensitive to the effects of butyrate on proliferation and apoptosis that are CRC cells. We further examine these gene expression patterns in butyrate-resistant vs. butyrate-sensitive CRC cells. Based upon all of these observations, we hypothesize that colonic neoplastic cells exhibiting a more oncogenic as compared to receptor-mediated Wnt signaling gene expression pattern would be more sensitive to the effects of butyrate, and, hence, fiber, than are those cells exhibiting a more receptor-mediated Wnt signaling pattern of expression. Diet-derived butyrate may affect the differential patient outcomes resulting from the two types of Wnt signaling. We further posit that development of butyrate resistance and concomitant changes in Wnt signaling patterns, including associations with CBP and p300, disrupts the association between the two major types of Wnt signaling (receptor-mediated and oncogenic) and neoplastic progression/prognosis. Ideas about testing the hypothesis and therapeutic implications are briefly considered.

Hypothesis: Mutations and Immunosurveillance in Obesity-Associated Colorectal Cancer

Tumorigenesis typically requires the accumulation of several driver gene mutations; therefore, there is a mutation threshold for the completion of the neoplastic process. Obesity increases the risk of cancer, and we have proposed that one mechanism whereby obesity raises the risk of microsatellite stable (MSS) colon cancer is by decreasing the mutation threshold. Therefore, obese MSS colon cancer patients should exhibit fewer driver gene mutations compared to normal body-mass index (BMI) patients. Our hypothesis is supported by results from analyses of The Cancer Genome Atlas (TCGA) data, which revealed that cancer genomes of obese MSS colon patients exhibit both fewer somatic mutations and fewer driver gene mutations. These findings could be explained by the high levels of obesity-associated cytokines and factors, the signaling pathways of which substitute for the additional driver gene mutations detected in normal-weight MSS colon cancer patients. Therefore, obesity-induced aberrant cell signaling might cooperate with initiating driver gene mutations to promote neoplastic development. Consistent with this possibility, we observed a lower number of KRAS mutations in high-BMI MSS colon cancer patients. This paper extends our hypothesis to address the interactions between obesity, immune surveillance in neoplastic development, and colorectal cancer (CRC) risk. A better understanding of these interactions will inform future preventive and therapeutic approaches against MSS CRC. We propose that the individual variations in the major histocompatibility class 1 (MHC-1) genotype interact with obesity to shape the tumor mutational landscape. Thus, the efficiency of the immune surveillance mechanisms to select against specific mutations may depend on both the MHC-1 genotype variant and the BMI of an individual. A high BMI is expected to reduce the number of driver gene mutations required to evade the MHC-1 surveillance mechanism and support an accelerated cancer progression.

Multifactorial causation of early onset colorectal cancer

The multiple-hit hypothesis of cancer, including colorectal cancer (CRC), states that neoplastic development requires a sequence of mutations and epigenetic changes in driver genes. We have previously proposed that obesity increases CRC risk by supporting neoplastic development through adipokine-induced signaling, and this proliferative signaling substitutes for specific driver gene mutations. In support of this hypothesis, analyses of The Cancer Genome Atlas (TCGA) mutation data have revealed that obese patients with microsatellite stable CRC exhibit fewer driver gene mutations than CRC patients with normal body mass index. The lower number of driver gene mutations required for cancer development may shorten the neoplastic process and lead to an early onset of CRC. Therefore, obesity could be one factor explaining the rise of CRC incidence among younger individuals (< 50 years of age); furthermore, early onset CRC has been associated with the increasing incidence of metabolic syndrome and obesity in this age group. However, CRC incidence among older individuals (> 50 years of age) is stable or declining, despite the high rates of metabolic syndrome and obesity in this age group. In search for explanations of this phenomenon, we discuss several factors that may contribute to the divergent CRC incidence trends in populations under, and above, the age of 50, despite the rising levels of metabolic syndrome and obesity across all ages. First, older individuals with metabolic dysregulation are more frequently on maintenance medications, such as aspirin, β-blockers, lipid-lowering drugs, ACE inhibitors, metformin, etc., compared to younger individuals. Such treatments may suppress specific adipokine-induced proliferative signaling pathways, and therefore counteract and slow down neoplastic development in medicated overweight/obese individuals. Second, in the past decades, the incidence of infectious diseases accompanied by febrile episodes has been decreasing and the use of antipyretics increasing. Compared to normal cells, neoplastic cells are more sensitive to high body temperature; therefore, the decreased number of febrile episodes in childhood and adolescence may contribute to increased cancer incidence before the age of 50. Third, obesity at younger age may expand the stem cell compartment. An increased number of intestinal stem cells and stem cell divisions translates into a higher probability of sporadic mutations in the stem cells, and therefore, a greater chance of neoplasia. In conclusion, we hypothesize that early onset CRC has multifactorial causation and the proposed associations could be examined through analyses of existing data.

Hypothesis: Sam68 and Pygo2 mediate cell type-specific effects of the modulation of CBP-Wnt and p300-Wnt activities in Colorectal Cancer Cells

The preventive activity of dietary fiber against colorectal cancer (CRC) may be in part mediated by the fermentation product of fiber, butyrate, a histone deacetylase inhibitor (HDACi) that induces CRC cell growth arrest and apoptosis. This action of butyrate, and other HDACis, is in part due to the hyperactivation of the deregulated Wnt activity found in the relevant CRC cell lines. The histone acetylases CBP and p300 interact with beta-catenin; and the relative levels of CBP-Wnt vs. p300-Wnt activity influences CRC cell physiology. It has previously been observed that there are cell type-specific differences in how cotreatment with butyrate and ICG-001, an agent that blocks CBP-Wnt activity allowing for p300-Wnt activity, affects CRC cell physiology. These differences may have clinical significance in dealing with treatment of CRC patients with ICG-001-like agents. Sam68 is a factor differentially expressed in cancer cells, with higher expression in cancer cell lines that have cancer stem cell (CSC)-like properties. Sam68 expression sensitizes cancer cells to ICG-001 treatment, as ICG-001 enhances nuclear localization of Sam68, where binding between Sam68 and CBP diminishes CBP-beta-catenin binding and thus CBP-Wnt activity. Pygo2 is a chromatin effector involved with Wnt signaling that is differentially acetylated by CBP and p300; thus CBP-mediated acetylation localized Pygo2 to the nucleus where it functions in transcriptional activation, while p300-mediated acetylation localizes Pygo2 to the cytoplasm. This paper proposes the hypothesis that Sam68 and Pygo2 are responsible for cell type-specific response of CRC cell lines cotreated with ICG-001 and butyrate as well as other HDACis. Further, experiments are proposed to evaluate this hypothesis and consider possible expected results that could be obtained from such studies.

Further analysis of p300 in mediating effects of Butyrate in Colorectal Cancer Cells

Butyrate, a product of dietary fiber, hyperactivates Wnt signaling in colorectal cancer (CRC) cells; this activity of butyrate is causally associated with the induction of apoptosis, and the repression of proliferation, in these cells. However, CRC can develop despite a high fiber diet; hence, butyrate resistance likely occurs during colonic neoplasia. To evaluate the mechanisms of butyrate resistance, HCT-116 CRC cells were previously made resistant to butyrate (HCT-R cell line); I observed that butyrate resistance in HCT-R cells is accompanied by repressed Wnt hyperactivation. CBP and p300 competitively bind to the Wnt signaling factor beta-catenin; CBP-Wnt activity is associated with proliferation, while p300-Wnt activity is associated with differentiation and apoptosis. While butyrate sensitive HCT-116 cells express p300, butyrate resistant HCT-R cells do not. Further, HCT-116 p300 knockout cells exhibit butyrate resistance, and restoration of p300 expression in these cells enhances butyrate sensitivity. Thus, p300 activity is a mediator of butyrate sensitivity in HCT-116-derived cell lines. In the present study, YH249, a pharmacological inhibitor of the p300-beta-catenin association, was utilized to more specifically evaluate the role of p300-Wnt signaling in butyrate responsiveness. Unexpectedly, YH249 potentiates butyrate-induced effects on apoptosis and cell proliferation in HCT-116 cells; in addition, potential off-target, p300-independent, effects of YH249 on butyrate-induced Wnt hyperactivation were observed. SW620 metastatic CRC cells express p300, but do not exhibit association of p300 with beta-catenin. Thus, I hypothesized that SW620 cells can be made butyrate resistant without loss of p300 expression, while butyrate resistance would still be associated with repressed Wnt hyperactivation; this hypothesis was confirmed. Thus, the data in toto suggest that while p300-Wnt activity is an important effector of butyrate sensitivity in some CRC cell lines, other, p300-independent pathways influencing butyrate sensitivity must also exist.

Hypothesis: Retinoblastoma protein inactivation mediates effects of histone deacetylase inhibitor-induced Wnt hyperactivation in colorectal cancer cells

Butyrate, a product of dietary fiber and a histone deacetylase inhibitor, induces apoptosis of colorectal cancer cells; this effect of butyrate is in part mediated by its ability to hyperactivate Wnt signaling, and may in part explain the preventive action of dietary fiber against colorectal cancer. However, the mechanisms by which Wnt hyperactivation promotes apoptosis are unknown. Inactivation of the retinoblastoma tumor suppressor occurs in some cancers and can lead to context-dependent cell proliferation or cell death/apoptosis. The function of retinoblastoma protein (Rb) in normal cells is modulation of cell cycle; inactivation of Rb allows for cell cycle progression and, hence, cell proliferation. Wnt signaling is upregulated in a variety of cancers, and deregulated Wnt signaling is a key initiating event in most cases of sporadic colorectal cancer. It has been shown that Wnt signaling activated by APC inactivation can synergize with the inactivation of Rb to induce apoptosis in a manner mediated by increased TORC1 activity, leading to induced metabolic and energy stress. Rb is typically not inactivated in colorectal cancer; however, Rb is phosphorylated and deactivated during cell cycle G1/S transition. This manuscript posits that it is during this time that butyrate/histone deacetylase inhibitor-induced Wnt hyperactivation induces apoptosis in colorectal cancer cells. Thus, the inactivation of Rb in cell cycle progression may synergize with Wnt hyperactivation to induce apoptosis in response to histone deacetylase inhibitors. The hypothesis is that hyperactivation of Wnt signaling enhances colorectal cancer cell apoptosis via the interaction between upregulated Wnt signaling and inactivated Rb during cell cycle progression. This paper discusses this hypothesis and offers initial experimental approaches for testing the hypothesis. A better understanding of how histone deacetylase inhibitors induce colorectal cancer cell apoptosis through hyperactivation of Wnt signaling, and of cross-talk between repression of cell cycle and induction of apoptosis that occurs with treatment with histone deacetylase inhibitors, can assist in the development of novel therapies for colorectal cancer.

Secondary Bile Acids and Short Chain Fatty Acids in the Colon: A Focus on Colonic Microbiome, Cell Proliferation, Inflammation, and Cancer

Secondary bile acids (BAs) and short chain fatty acids (SCFAs), two major types of bacterial metabolites in the colon, cause opposing effects on colonic inflammation at chronically high physiological levels. Primary BAs play critical roles in cholesterol metabolism, lipid digestion, and host–microbe interaction. Although BAs are reabsorbed via enterohepatic circulation, primary BAs serve as substrates for bacterial biotransformation to secondary BAs in the colon. High-fat diets increase secondary BAs, such as deoxycholic acid (DCA) and lithocholic acid (LCA), which are risk factors for colonic inflammation and cancer. In contrast, increased dietary fiber intake is associated with anti-inflammatory and anticancer effects. These effects may be due to the increased production of the SCFAs acetate, propionate, and butyrate during dietary fiber fermentation in the colon. Elucidation of the molecular events by which secondary BAs and SCFAs regulate colonic cell proliferation and inflammation will lead to a better understanding of the anticancer potential of dietary fiber in the context of high-fat diet-related colon cancer. This article reviews the current knowledge concerning the effects of secondary BAs and SCFAs on the proliferation of colon epithelial cells, inflammation, cancer, and the associated microbiome.

Amlexanox and UPF1 Modulate Wnt Signaling and Apoptosis in HCT-116 Colorectal Cancer Cells

Deregulated Wnt signaling initiates most cases of colorectal cancer (CRC). Butyrate, a product of dietary fiber, hyperactivates Wnt signaling, resulting in induction of CRC cell apoptosis, which may in part explain the protective action of fiber. Nonsense mediated decay (NMD) of mRNAs containing premature stop codons (PTCs) affects tumorigenesis and upregulates Wnt signaling in human embryonic stem cells. However, it is unknown how NMD affects Wnt activity in CRC cells that exhibit constitutively activated Wnt signaling. We hypothesize that expression of genes that contain PTCs modulates Wnt signaling and response to butyrate in CRC cells. Amlexanox is a clinically utilized anti-allergic and anti-inflammatory drug that inhibits NMD and promotes PTC read-through. Therefore, Amlexanox is a relevant agent for assessing the role of NMD and PTC read-through in the response of CRC cells to butyrate. To test our hypothesis, we treated HCT-116 CRC cells with Amlexanox and determined effects on Wnt signaling levels, apoptosis, and response to butyrate. Amlexanox enhanced basal Wnt signaling levels; however, it repressed butyrate-induced Wnt signaling hyperactivation and suppressed apoptosis. To evaluate the contribution of NMD and altered expression of PTC-containing genes to these effects, we upregulated NMD by overexpression of up-frameshift protein 1 (UPF1), and observed effects opposite to these of Amlexanox (i.e., Wnt signaling hyperactivation by butyrate was enhanced and levels of apoptosis were increased). Our results support the possibility that altered expression of PTC-containing genes affects butyrate sensitivity of CRC cells.

Hypothesis: Cancer Is a Disease of Evolved Trade-Offs Between Neoplastic Virulence and Transmission

Virulence is defined as the ability of a pathogen to cause morbidity and/or mortality in infected hosts. The relationship between virulence and transmissibility is complex; natural selection may promote decreased virulence to enhance host mobility and increase the probability for transmission, or transmissibility may be enhanced by increased virulence, leading to higher pathogen load and, in some cases, superior evasion from host defenses. An evolutionary trade-off exists between the ability of pathogens to maintain opportunities for long-term transmission via suppressed virulence and increased short-term transmission via enhanced virulence. We propose an analogy between transmissibility and virulence in microbial pathogens and in cancer. Thus, in the latter case, the outcome of invasive growth and metastasis is analogous to transmissibility, and virulence is defined by high rates of proliferation, invasiveness and motility, potential for metastasis, and the extent to which the cancer contributes to patient morbidity and mortality. Horizontal and vertical transmission, associated with increased or decreased pathogen virulence respectively, can also be utilized to model the neoplastic process and factors that would increase or decrease tumor aggressiveness. Concepts of soft vs. hard selection and evolutionary game theory can optimize our understanding of carcinogenesis and therapeutic strategies. Therefore, the language of transmissibility, horizontal vs. vertical transmission, selection, and virulence can be used to inform approaches to inhibit tumorigenic progression, and, more generally, for cancer prevention and treatment.

Hypothesis: Induction of biomarkers for detection of colonic neoplasms

The signing of the National Cancer Act of 1971 by President Nixon marked the beginning of our war on cancer. More than 45 years later, the war is still going steady, with the enemy being almost as strong as in 1971. Furthermore, the increasing rates of obesity not only among adults, but among children and adolescents, are the likely cause for the 30-year trend of colon cancer (CC) becoming a disease of the younger population in the U.S. These trends, however, have not spurred the development of novel screening approaches for CC. Considering the need for a sensitive and non-invasive detection of early stage neoplastic lesions in the colon, we propose the development of a test based on a novel concept - the concept of induced biomarkers. The proposal is based upon our findings that the food additives propolis and gamma-cyclodextrin (gCD) (a) decrease the neoplastic burden in normal weight and obese Apc^Min mice, a model of early stage intestinal neoplasia, and (b) elicit significant changes in the serum proteome in Apc^Min mice. We posit that gCD and propolis induce the release of neoplasm-associated biomarkers in systemic circulation (e.g., metabolites, neoplastic, apoptotic, and immune response proteins), and these markers could be used to detect early stage intestinal neoplasms. Additional dietary bioactives may also elicit a complement of induced markers. The hypothesis could be ascertained by utilizing a mouse model, the Apc^+/1638Nmice, as well as through human subject studies that integrate proteomics and metabolomics analyses. The concept of detecting inducible markers of colonic neoplasms is novel, and is substantiated by the significant physiological effects of gCD and propolis on neoplastic colonic cells in culture and on early neoplastic development in Apc^Minmice. The long-term objective is to develop a minimally invasive method that detects early stage neoplastic development in the human colon.

p300 Knockout Promotes Butyrate Resistance

Dietary fiber is linked to a reduced risk of colorectal cancer (CRC), and this protective activity is likely due to its fermentation product, butyrate. Dependent upon the hyperactivation of Wnt signaling, butyrate represses CRC cell growth and induces apoptosis. However, resistance to butyrate activity may allow for CRC development even in the context of relatively high fiber intake. We have previously determined that CRC cells resistant to butyrate are deficient in p300 expression. The histone acetylase p300 influences colonic cell signaling and physiology through effects on Wnt signaling. In this short research communication, we report that p300 knockout CRC cells exhibit butyrate resistance, and the re-introduction of p300 expression in p300 knockout CRC cells restores butyrate sensitivity. Microarray data on gene expression associated with butyrate sensitivity are presented and discussed.

ZEB1 Mediates Drug Resistance and EMT in p300-Deficient CRC

We discuss the hypothesis that ZEB1-Wnt-p300 signaling integrates epithelial to mesenchymal transition (EMT) and resistance to histone deacetylase inhibitors (HDACis) in colorectal cancer (CRC) cells. The HDACi butyrate, derived from dietary fiber, has been linked to CRC prevention, and other HDACis have been proposed as therapeutic agents against CRC. We have previously discussed that resistance to butyrate likely contributes to colonic carcinogenesis, and we have demonstrated that butyrate resistance leads to cross-resistance to cancer therapeutic HDACis. Deregulated Wnt signaling is the major initiating event in most CRC cases. One mechanism whereby butyrate and other HDACis exert their anti-CRC effects is via Wnt signaling hyperactivation, which promotes CRC cell apoptosis. The histone acetylases (HATs) CBP and p300 are mediators of Wnt transcriptional activity, and play divergent roles in the downstream consequences of Wnt signaling. CBP-mediated Wnt signaling is associated with cell proliferation and stem cell maintenance; whereas, p300-mediated Wnt activity is associated with differentiation. We have found that CBP and p300 differentially affect the ability of butyrate to influence Wnt signaling, apoptosis, and proliferation. ZEB1 is a Wnt signaling-targeted gene, whose product is a transcription factor expressed at the invasive front of carcinomas where it promotes malignant progression and EMT. ZEB1 is typically a transcriptional repressor; however, when associated with p300, ZEB1 enhances transcription. These changes in ZEB1 activity likely affect the cancer cell phenotype. ZEB1 has been shown to promote resistance to chemotherapeutic agents, and expression of ZEB1 is upregulated in butyrate-resistant CRC cells that lack p300 expression. Since the expression of ZEB1 correlates with poor outcomes in cancer, ZEB represents a relevant therapeutic target. Here we propose that targeting the signaling network established by ZEB1, Wnt signaling, and p300 signaling can reverse HDACi resistance and inhibit EMT.

Effects of propolis and gamma-cyclodextrin on intestinal neoplasia in normal weight and obese mice

Obesity is associated with colorectal cancer (CRC). This effect might be attributed to adipokine‐supported signaling. We have established that propolis suppresses survival signaling in CRC cells in vitro; therefore, we ascertained the ability of a propolis supplement to modulate intestinal neoplastic development in C57BL/6J‐ApcMin/+/J mice in the lean and obese state. To induce obesity, mice were fed with a Western diet containing 40% fat. Since the propolis supplement includes gamma‐cyclodextrin, the interventions included diets supplemented with or without gamma‐cyclodextrin. The animals were administered the following diets: (1) control diet, (2) control diet/gamma‐cyclodextrin, (3) control diet/propolis, (4) Western diet, (5) Western diet/gamma‐cyclodextrin, and (6) Western diet/propolis. Western diet, resulting in obesity, accelerated neoplastic progression, as evidenced by the larger size and higher grade dysplasia of the neoplasms. In the context of normal weight, gamma‐cyclodextrin and propolis affected neoplastic progression, as determined by the size of the lesions and their grade of dysplasia. A statistically significant decrease in the number of adenomas was detected in mice fed a control diet with the propolis supplement (61.8 ± 10.6 vs. 35.3 ± 7.6, P = 0.008). Although there was no significant difference in the polyp numbers between the six groups, the mice with the lowest number and size of adenomas were those fed a Western diet with gamma‐cyclodextrin. This unexpected outcome might be explained by the increased levels of apoptosis detected in the intestinal tissues of these obese mice. We posit that butyrate derived from the metabolism of gamma‐cyclodextrin may contribute to the decreased neoplastic burden in the context of obesity; however, future studies are required to address this possibility.

In Hyperthermia Increased ERK and WNT Signaling Suppress Colorectal Cancer Cell Growth

Although neoplastic cells exhibit relatively higher sensitivity to hyperthermia than normal cells, hyperthermia has had variable success as an anti-cancer therapy. This variable outcome might be due to the fact that cancer cells themselves have differential degrees of sensitivity to high temperature. We hypothesized that the varying sensitivity of colorectal cancer (CRC) cells to hyperthermia depends upon the differential induction of survival pathways. Screening of such pathways revealed that Extracellular Signal-Regulated Kinase (ERK) signaling is augmented by hyperthermia, and the extent of this modulation correlates with the mutation status of V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS). Through clonal growth assays, apoptotic analyses and transcription reporter assays of CRC cells that differ only in KRAS mutation status we established that mutant KRAS cells are more sensitive to hyperthermia, as they exhibit sustained ERK signaling hyperactivation and increased Wingless/Integrated (WNT)/beta-catenin signaling. We propose that whereas increased levels of WNT and ERK signaling and a positive feedback between the two pathways is a major obstacle in anti-cancer therapy today, under hyperthermia the hyperinduction of the pathways and their positive crosstalk contribute to CRC cell death. Ascertaining the causative association between types of mutations and hyperthermia sensitivity may allow for a mutation profile-guided application of hyperthermia as an anti-cancer therapy. Since KRAS and WNT signaling mutations are prevalent in CRC, our results suggest that hyperthermia-based therapy might benefit a significant number, but not all, CRC patients.

Determination of the Role of CBP- and p300-Mediated Wnt Signaling on Colonic Cells

BACKGROUND

The Wnt signaling pathway, mediated through active beta-catenin, is responsible for initiating the majority of cases of human colorectal cancer (CRC), and we have previously shown that hyperactivation of this pathway by histone deacetylase inhibitors (HDACis), such as butyrate, can induce the death of CRC cells. An important cellular switch that mediates the effects of Wnt-signaling activation is variation in the association between beta-catenin and the transcriptional coactivators cAMP response element binding (CREB) binding protein (CBP) and p300. Association of CBP with beta-catenin is thought to activate a set of genes linked to cell proliferation, while the p300-mediated Wnt genetic program is believed to promote cell differentiation. Small molecule agents have been discovered that modulate CBP/p300 Wnt transcriptional programs by altering the association of CBP and p300 to beta-catenin. ICG-001 and ICG-427 inhibit CBP- and p300-mediated Wnt activity, respectively, while IQ-1 prevents the shift from CBP-mediated to a p300-mediated Wnt activity.

OBJECTIVE

Aim 1 of this proposal is designed to determine the role of CBP- and p300-mediated Wnt signaling in the response of CRC cells to HDACis. Aim 2 is to determine the role of CBP and p300 in the maintenance of high- and low-Wnt fractions in CRC cell line. Aim 3 will compare the effects of CBP- and p300-mediated Wnt activity on CRC initiation and progression.

METHODS

In Aim 1, cells will be cotreated with HDACis and ICG-001, ICG-427, or IQ-1 and the levels of Wnt activity, apoptosis, proliferation, differentiation, and CBP- or p300-beta-catenin binding measured. Aim 2 of this proposal may mirror similar heterogeneity observed in human tumors and which may be of clinical significance. Aim 3 will use CRC cell line model systems of initiation and progression: the normal colon cell lines CCD-841CoN, the adenoma line LT97, the primary colon carcinoma cell line SW480, and the lymph node metastasis cell line SW620. Cells will be treated with HDACis and the small molecule agents, and assayed as described above.

RESULTS

We will also attempt to use changes in CBP- and p300-mediated Wnt signaling to shift colonic cells between cell type, modifying CBP- and p300-mediated gene expression in the LT97 adenoma line to shift the adenoma phenotype to more characteristic of the CCD-841CoN normal cells, or the SW480 carcinoma cells. We will use microarray analyses to determine the patterns of gene expression responsible for these CBP- or p300-mediated changes in colonic neoplastic phenotype.

CONCLUSIONS

The findings generated from this study will lead to future, more in-depth projects to further dissect the action of CBP/p300 Wnt-mediated transcriptional programs in colonic neoplasia, with an emphasis on methods to modulate these genetic programs for chemopreventive effect.

Vimentin, colon cancer progression and resistance to butyrate and other HDACis

Dietary fibre protects against colorectal cancer (CRC) most likely through the activity of its fermentation product, butyrate. Butyrate functions as a histone deacetylase inhibitor (HDACi) that hyperactivates Wnt signalling and induces apoptosis of CRC cells. However, individuals who consume a high‐fibre diet may still develop CRC; therefore, butyrate resistance may develop over time. Furthermore, CRC cells that are resistant to butyrate are cross‐resistant to clinically relevant therapeutic HDACis, suggesting that the development of butyrate resistance in vivo can result in HDACi‐resistant CRCs. Butyrate/HDACi‐resistant CRC cells differ from their butyrate/HDACi‐sensitive counterparts in the expression of many genes, including the gene encoding vimentin (VIM) that is usually expressed in normal mesenchymal cells and is involved in cancer metastasis. Interestingly, vimentin is overexpressed in butyrate/HDACi‐resistant CRC cells although Wnt signalling is suppressed in such cells and that VIM is a Wnt activity‐targeted gene. The expression of vimentin in colonic neoplastic cells could be correlated with the stage of neoplastic progression. For example, comparative analyses of LT97 microadenoma cells and SW620 colon carcinoma cells revealed that although vimentin is not detectable in LT97 cells, it is highly expressed in SW620 cells. Based upon these observations, we propose that the differential expression of vimentin contributes to the phenotypic differences between butyrate‐resistant and butyrate‐sensitive CRC cells, as well as to the differences between early‐stage and metastatic colorectal neoplastic cells. We discuss the hypothesis that vimentin is a key factor integrating epithelial to mesenchymal transition, colonic neoplastic progression and resistance to HDACis.

CREB-binding protein, p300, butyrate, and Wnt signaling in colorectal cancer

This paper reviews the distinctive roles played by the transcriptional coactivators CREB-binding protein (CBP) and p300 in Wnt/β-catenin signaling and cell physiology in colorectal cancer (CRC). Specifically, we focus on the effects of CBP- and p300-mediated Wnt activity on (1) neoplastic progression; (2) the activities of butyrate, a breakdown product of dietary fiber, on cell signaling and colonic cell physiology; (3) the development of resistance to histone deacetylase inhibitors (HDACis), including butyrate and synthetic HDACis, in colonic cells; and (4) the physiology and number of cancer stem cells. Mutations of the Wnt/β-catenin signaling pathway initiate the majority of CRC cases, and we have shown that hyperactivation of this pathway by butyrate and other HDACis promotes CRC cell apoptosis. This activity by butyrate may in part explain the preventive action of fiber against CRC. However, individuals with a high-fiber diet may still develop neoplasia; therefore, resistance to the chemopreventive action of butyrate likely contributes to CRC. CBP or p300 may modify the ability of butyrate to influence colonic cell physiology since the two transcriptional coactivators affect Wnt signaling, and likely, its hyperactivation by butyrate. Also, CBP and p300 likely affect colonic tumorigenesis, as well as stem cell pluripotency. Improvement of CRC prevention and therapy requires a better understanding of the alterations in Wnt signaling and gene expression that underlie neoplastic progression, stem cell fate, and the development of resistance to butyrate and clinically relevant HDACis. Detailed knowledge of how CBP- and p300 modulate colonic cell physiology may lead to new approaches for anti-CRC prevention and therapeutics, particularly with respect to combinatorial therapy of CBP/p300 inhibitors with HDACis.

Hypothesis: Obesity Is Associated with a Lower Mutation Threshold in Colon Cancer

Neoplastic progression requires accumulation of several mutations (mutation threshold). We hypothesize that obesity raises the risk of microsatellite stable (MSS) colon cancer (CC) at least in part by decreasing the mutation threshold. Thus, we posit that obese patients require fewer mutations, particularly driver mutations, compared to their normal BMI counterparts. Further, we suggest that the reduced number of required mutations in obese patients could be due to several factors, including the high levels of cytokines that accompany obesity. Cytokine-activated ERK, AKT, and JAK/STAT signaling could synergize with CC-initiating mutations to promote intestinal neoplastic development. Therefore, driver mutations that induce these specific pathways may not be “required” for neoplastic development in obesity; alteration in cell signaling consequent to obesity can substitute for some driver mutations in neoplastic progression. This hypothesis is supported by preliminary analyses of data from The Cancer Genome Atlas (TCGA). Thus, we observed that, compared to normal weight patients, cancer genomes of obese MSS CC patients exhibit fewer somatic mutations, and correspondingly lower numbers of mutations in driver genes (P = 0.026).The most striking observation was the lower number of KRAS mutations detected in patients with high body-mass index (BMI). These intriguing observations require further validation with increased number of patients, taking into account all possible confounding factors. If the hypothesis is confirmed, future studies should also address several possible explanations for the observed lower mutation threshold in obese MSS CC patients.

Hypothesis: cell signalling influences age-related risk of colorectal cancer

We propose that ageing is linked to colonic carcinogenesis through crosstalk between Wnt activity and signalling pathways related to ageing and senescence: progerin, klotho and mTOR. Mutations in the Wnt signalling pathway are responsible for the majority of colorectal cancers (CRCs); however, hyperactivation of Wnt signalling by butyrate, a breakdown product of dietary fibre, induces CRC cell apoptosis. This effect of butyrate may in part explain the protective action of fibre against CRC. Hutchinson-Gilford progeria syndrome is a premature ageing disorder caused by accumulation of the progerin protein; however, healthy individuals also produce progerin in the course of their normal ageing. Progerin activates expression of the Wnt inhibitors HES1 and TLE1. Thus, we hypothesize that with age, the increasing expression of progerin suppresses butyrate-mediated Wnt hyperactivation and apoptosis, leading to increased CRC risk. Wild-type klotho contributes to a significantly increased lifespan; however, Klotho gene variants differ significantly between newborns and elderly. Klotho inhibits basal Wnt signalling activity; thus, the protein may function as a tumour suppressor for CRC. However, similar to progerin, klotho variants associated with lifespan differences may repress butyrate-mediated Wnt hyperactivation, and thus increase the risk of CRC. Finally, mTOR signalling has also been linked to human ageing, and crosstalk between Wnt and mTOR signalling may influence colonic tumourigenesis. Understanding how progerin, klotho and mTOR link ageing with colonic neoplastic development may lead to novel preventive and therapeutic strategies against CRC associated with age.

Comprehensive suppression of all apoptosis-induced proliferation pathways as a proposed approach to colorectal cancer prevention and therapy

Mutations in the WNT/beta-catenin pathway are present in the majority of all sporadic colorectal cancers (CRCs), and histone deacetylase inhibitors induce apoptosis in CRC cells with such mutations. This apoptosis is counteracted by (1) the signaling heterogeneity of CRC cell populations, and (2) the survival pathways induced by mitogens secreted from apoptotic cells. The phenomena of signaling heterogeneity and apoptosis-induced survival constitute the immediate mechanisms of resistance to histone deacetylase inhibitors, and probably other chemotherapeutic agents. We explored the strategy of augmenting CRC cell death by inhibiting all survival pathways induced by the pro-apoptotic agent LBH589, a histone deacetylase inhibitor: AKT, JAK/STAT, and ERK signaling. The apoptosis-enhancing ability of a cocktail of synthetic inhibitors of proliferation was compared to the effects of the natural product propolis. We utilized colorectal adenoma, drug-sensitive and drug-resistant colorectal carcinoma cells to evaluate the apoptotic potential of the combination treatments. The results suggest that an effective approach to CRC combination therapy is to combine apoptosis-inducing drugs (e.g., histone deacetylase inhibitors, such as LBH589) with agents that suppress all compensatory survival pathways induced during apoptosis (such as the cocktail of inhibitors of apoptosis-associated proliferation). The same paradigm can be applied to a CRC prevention approach, as the apoptotic effect of butyrate, a diet-derived histone deacetylase inhibitor, is augmented by other dietary agents that modulate survival pathways (e.g., propolis and coffee extract). Thus, dietary supplements composed by fermentable fiber, propolis, and coffee extract may effectively counteract neoplastic growth in the colon.

Experimental design to evaluate directed adaptive mutation in Mammalian cells

BACKGROUND

We describe the experimental design for a methodological approach to determine whether directed adaptive mutation occurs in mammalian cells. Identification of directed adaptive mutation would have profound practical significance for a wide variety of biomedical problems, including disease development and resistance to treatment. In adaptive mutation, the genetic or epigenetic change is not random; instead, the presence and type of selection influences the frequency and character of the mutation event. Adaptive mutation can contribute to the evolution of microbial pathogenesis, cancer, and drug resistance, and may become a focus of novel therapeutic interventions.

OBJECTIVE

Our experimental approach was designed to distinguish between 3 types of mutation: (1) random mutations that are independent of selective pressure, (2) undirected adaptive mutations that arise when selective pressure induces a general increase in the mutation rate, and (3) directed adaptive mutations that arise when selective pressure induces targeted mutations that specifically influence the adaptive response. The purpose of this report is to introduce an experimental design and describe limited pilot experiment data (not to describe a complete set of experiments); hence, it is an early report.

METHODS

An experimental design based on immortalization of mouse embryonic fibroblast cells is presented that links clonal cell growth to reversal of an inactivating polyadenylation site mutation. Thus, cells exhibit growth only in the presence of both the countermutation and an inducing agent (doxycycline). The type and frequency of mutation in the presence or absence of doxycycline will be evaluated. Additional experimental approaches would determine whether the cells exhibit a generalized increase in mutation rate and/or whether the cells show altered expression of error-prone DNA polymerases or of mismatch repair proteins.

RESULTS

We performed the initial stages of characterizing our system and have limited preliminary data from several pilot experiments. Cell growth and DNA sequence data indicate that we have identified a cell clone that exhibits several suitable characteristics, although further study is required to identify a more optimal cell clone.

CONCLUSIONS

The experimental approach is based on a quantum biological model of basis-dependent selection describing a novel mechanism of adaptive mutation. This project is currently inactive due to lack of funding. However, consistent with the objective of early reports, we describe a proposed study that has not produced publishable results, but is worthy of report because of the hypothesis, experimental design, and protocols. We outline the project's rationale and experimental design, with its strengths and weaknesses, to stimulate discussion and analysis, and lay the foundation for future studies in this field.

Butyrate induced changes in Wnt-signaling specific gene expression in colorectal cancer cells

BACKGROUND

We have determined that butyrate, which is derived from the fermentation of dietary fiber in the colonic lumen, hyperactivates Wnt activity in colorectal (CRC) cells, and that this upregulation of Wnt signaling is causatively related to the induction of apoptosis. To better understand the genetic program regulated by butyrate-mediated Wnt hyperactivation, we performed total human genome microarray analyses on HCT-116 CRC cells in the presence or absence of a physiologically relevant concentration of butyrate. To evaluate changes in Wnt-specific gene expression, Wnt activity was suppressed with inducible dominant negative Tcf4 (DN-Tcf4). Six biological replicates of a full human genome microarray were performed, and the data deposited into the Gene Expression Omnibus database, according to Minimum Information About A Microarray Experiment standards.

RESULTS

Reporter assay and western blot data confirm that DN-Tcf4 is expressed at high levels in stably transfected HCT-116 cells upon cotreatment with doxycycline and butyrate, and that these cells exhibit a marked repression of butyrate-mediated Wnt hyperactivation. Analysis of six biological replicates of microarray analyses indicated that 1008 genes are modulated by butyrate (>two-fold, P < 0.01) in a Wnt signaling-specific manner, while 1587 genes are similarly modulated at P < 0.05. The modulated genes include members of a variety of gene families; including the Biological Process category, such as regulation of development, regulation of metabolism, cytokine and chemokine mediated signaling pathways, and DNA replication; the Cellular Component category such as cytoskeleton and organelle factors, and intermediate filaments; and the Molecular Function category, such as GTPase activator activity.

CONCLUSIONS

We have identified, for the first time, in CRC cells, the total array of direct and indirect Wnt-target genes whose expression is modulated by butyrate. Knowledge of the molecular mechanisms determining the response of CRC cells to butyrate in vitro may assist in determining more effective preventive and therapeutic strategies against CRC.

Mechanisms linking dietary fiber, gut microbiota and colon cancer prevention

Many epidemiological and experimental studies have suggested that dietary fiber plays an important role in colon cancer prevention. These findings may relate to the ability of fiber to reduce the contact time of carcinogens within the intestinal lumen and to promote healthy gut microbiota, which modifies the host’s metabolism in various ways. Elucidation of the mechanisms by which dietary fiber-dependent changes in gut microbiota enhance bile acid deconjugation, produce short chain fatty acids, and modulate inflammatory bioactive substances can lead to a better understanding of the beneficial role of dietary fiber. This article reviews the current knowledge concerning the mechanisms via which dietary fiber protects against colon cancer.

Modulation of Wnt Activity and Cell Physiology by Butyrate in LT97 Microadenoma Cells

Dietary fiber intake is linked to a reduced risk of colon cancer. This effect may in part be due to butyrate, the fermentation product of fiber in the colon. Butyrate is a short-chain fatty acid that acts as a histone deacetylase inhibitor (HDACi). Butyrate induces apoptosis and represses clonal growth of colorectal cancer (CRC) cells, in a manner dependent upon the hyperactivation of Wnt /beta-catenin signaling. While fiber has been linked to CRC prevention, in vitro studies on the action of butyrate have used CRC cell lines, instead of cells representative of earlier stages of colonic neoplasia, which are the likely target of butyrate-mediated preventive activity. The LT97 cell line is derived from a microadenoma, the earliest stage of colonic neoplasia from which cells can be isolated. We characterized LT97 cells with respect to effects of butyrate on Wnt signaling and apoptosis, and we determined whether modulation of CREB binding protein (CBP)/p300 activity influences the ability of butyrate to induce Wnt activity and apoptosis. We report that in LT97 cells, butyrate induces apoptosis, strongly upregulates Wnt signaling, and the upregulation of Wnt signaling is dependent upon CBP/p300 activity. In addition, findings from overexpression experiments suggest differences between CBP and p300 in their ability to influence Wnt signaling in LT97 cells; p300, but not CBP, stimulates basal Wnt activity. We also evaluated differences in gene expression between early stage LT97 cells and late stage metastatic SW620 CRC cells that exhibit markedly different cellular phenotypes. The comparative gene expression analyses revealed differences that may impact neoplastic progression and the sensitivity to the effects of butyrate. The findings have implications for the prevention of CRC by fiber/butyrate.

Approaches that ascertain the role of dietary compounds in colonic cancer cells

Preventive approaches against cancer have not been fully developed and applied. For example, the incidence of some types of cancer, including colon cancer, is highly dependent upon lifestyle, and therefore, amenable to prevention. Among the lifestyle factors, diet strongly affects the incidence of colon cancer; however, there are no definitive dietary recommendations that protect against this malignancy. The association between diet-derived bioactives and development of colonic neoplasms will remain ill defined if we do not take into account: (1) the identity of the metabolites present in the colonic lumen; (2) their concentrations in the colon; and (3) the effect of the colonic contents on the function of individual bioactives. We review two approaches that address these questions: the use of fecal water and in vitro models of the human colon. Compared to treatment with individual diet-derived compounds, the exposure of colon cancer cells to samples from fecal water or human colon simulators mimics closer the in vitro conditions and allows for more reliable studies on the effects of diet on colon cancer development. The rationale and the advantages of these strategies are discussed from the perspective of a specific question on how to analyze the combined effect of two types of bioactives, butyrate and polyphenol metabolites, on colon cancer cells.

Abstract A26: Colon cancer prevention through combinations of dietary or pharmacological agents

Our studies aim at developing combinations of dietary or pharmacological agents that lower the risk for colorectal cancer (CRC). In vitrostudies have demonstrated that histone deacetylase inhibitors (HDACis) induce programmed death (apoptosis) in CRC cells with mutations in the WNT/beta-catenin pathway, and the apoptotic levels depend upon the hyperactivation of WNT signaling. Since mutations in the WNT/catenin pathway are present in almost 80% of all sporadic CRCs, dietary and synthetic HDACis are promising anti-CRC agents.

However, HDACi-initiated apoptosis of CRC cells is counteracted by induction of compensatory proliferation supported by the AKT and JAK/STAT cell survival pathways. Therefore, we ascertained whether agents that suppress cell survival signaling augment the apoptotic effect of HDACis. We utilized apoptotic assays and immunoblotting analyses to ascertain the ability of compensatory pathway inhibitors to augment the apoptosis induced by dietary and pharmacological HDACis in colorectal neoplastic cells. The effects of the agents were assessed in HDACi-resistant colorectal cancer (HCT-R) and early colonic adenoma (LT97) cells.

A combination treatment of CRC cells with a synthetic HDACi (LBH589), an AKT inhibitor (MK2206), and a JAK/STAT inhibitor (pyridone 6) validated the concept that the apoptotic effect of a HDACi is augmented by inhibitors of compensatory proliferation. Such pharmacological approach to CRC prevention might be applicable for populations at high risk for colon cancer (e.g., CRC patients with partial colonic resection, chronic inflammatory bowel disease, history of colonic polyps).

Interestingly, diet-derived modulators of compensatory survival pathways affect differently HDACi-induced apoptosis in colonic carcinoma and early adenoma cells. Thus, caffeic acid phenethyl ester (CAPE, an AKT inhibitor contained in some honeybee propolis), and gallotannin (a JAK/STAT inhibitor derived from some fruit and wine) augment the apoptotic effect of the dietary HDACi butyrate in colonic carcinoma HCT-R cells, but not in adenoma LT97 cells. Resveratrol and pterostilbene (phenols found in grapes and blueberries) both suppress butyrate-induced apoptosis in colorectal carcinoma HCT-R cells, and augment butyrate-induced apoptosis in early adenoma cells in the presence of CAPE. Since at physiologically achievable concentrations CAPE, gallotannin, resveratrol, and pterostilbene alone or in combination do not induce apoptosis, the signaling pathways targeted by these compounds in butyrate-treated colonic neoplastic cells are true apoptosis-induced compensatory proliferation pathways. Our data suggest that different compensatory proliferation pathways are activated in colonic adenoma and carcinoma cells in response to the diet-derived HDACi butyrate. Further analyses should ascertain the identity of these cell survival signaling pathways.

In conclusion, the rationale of combining inducers of apoptosis (e.g., HDACis) with inhibitors of compensatory proliferation may result in the design of supplements with a powerful CRC-protective effect. The next step in the development of such dietary supplements is ascertaining their effect in animal models of intestinal cancer.

Citation Format: Eric Drago, Michael Bordonaro, Jeffrey Marteslo, Patricia Melvin, Wafa Atamna, Darina Lazarova. Colon cancer prevention through combinations of dietary or pharmacological agents. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A26.

Propolis augments apoptosis induced by butyrate via targeting cell survival pathways

Diet is one of the major lifestyle factors affecting incidence of colorectal cancer (CC), and despite accumulating evidence that numerous diet-derived compounds modulate CC incidence, definitive dietary recommendations are not available. We propose a strategy that could facilitate the design of dietary supplements with CC-preventive properties. Thus, nutrient combinations that are a source of apoptosis-inducers and inhibitors of compensatory cell proliferation pathways (e.g., AKT signaling) may produce high levels of programmed death in CC cells. Here we report the combined effect of butyrate, an apoptosis inducer that is produced through fermentation of fiber in the colon, and propolis, a honeybee product, on CC cells. We established that propolis increases the apoptosis of CC cells exposed to butyrate through suppression of cell survival pathways such as the AKT signaling. The programmed death of CC cells by combined exposure to butyrate and propolis is further augmented by inhibition of the JNK signaling pathway. Analyses on the contribution of the downstream targets of JNK signaling, c-JUN and JAK/STAT, to the apoptosis of butyrate/propolis-treated CC cells ascertained that JAK/STAT signaling has an anti-apoptotic role; whereas, the role of cJUN might be dependent upon regulatory cell factors. Thus, our studies ascertained that propolis augments apoptosis of butyrate-sensitive CC cells and re-sensitizes butyrate-resistant CC cells to apoptosis by suppressing AKT signaling and downregulating the JAK/STAT pathway. Future in vivo studies should evaluate the CC-preventive potential of a dietary supplement that produces high levels of colonic butyrate, propolis, and diet-derived JAK/STAT inhibitors.

p300 Influences Butyrate-Mediated WNT Hyperactivation In Colorectal Cancer Cells

Deregulated WNT/catenin pathway, usually resulting from mutations in the adenomatous polyposis coli and beta-catenin genes, drives colorectal tumorigenesis. Dietary fiber has been shown to have a protective role against colorectal cancer (CRC). We have previously demonstrated that the histone deacetylase inhibitor (HDACi) butyrate, a fermentation product of dietary fiber, induces WNT/catenin hyperactivation, which promotes CRC cell apoptosis. Therefore, the ability of butyrate to induce WNT hyperactivation and thus promote CRC cell apoptosis may in part explain the preventive function of fiber against CRC. The association between beta-catenin and the transcriptional coactivator p300 may influence WNT/catenin signaling and, therefore, colonic cell physiology. p300 functions as a histone acetylase (HAT); therefore, the modulation of WNT/catenin activity by p300 may influence the ability of the HDACi butyrate to hyperinduce WNT signaling and apoptosis in CRC cells. Our findings indicate that p300 affects the hyperinduction of WNT activity by butyrate. Knockdown of p300 levels represses butyrate-mediated WNT/catenin activity; but still allows for butyrate-mediated apoptosis. Overexpression of p300 stimulates basal and butyrate-induced WNT signaling in some, but not all, CRC cell lines. We also evaluate the role of p300 in therapeutic approaches that target CBP. The small molecule ICG-001, in clinical trial, is a specific inhibitor of CBP-mediated WNT signaling, and previous studies have suggested that p300 is required for the activity of ICG-001. However, we report that ICG-001 maintains full activity against CBP-mediated WNT signaling in p300-deficient cell lines, including the butyrate-resistance line HCT-R. In addition, our findings evaluating combinatorial treatment of ICG-001 and butyrate in HCT-R cells may have important therapeutic implications for the treatment of butyrate-resistant CRCs.

CBP Activity Mediates Effects of the Histone Deacetylase Inhibitor Butyrate on WNT Activity and Apoptosis in Colon Cancer Cells

Mutations in the WNT/beta-catenin pathway are responsible for initiating the majority of colorectal cancers (CRCs). We have previously shown that hyperactivation of this signaling by histone deacetylase inhibitors (HDACis) such as butyrate, a fermentation product of dietary fiber, promotes CRC cell apoptosis. The extent of association between beta-catenin and the transcriptional coactivator CREB-binding protein (CBP) influences WNT/catenin signaling and, therefore, colonic cell physiology. CBP functions as a histone acetylase (HAT); therefore, we hypothesized that the modulation of WNT/catenin activity by CBP modifies the ability of the HDACi butyrate to hyperinduce WNT signaling and apoptosis in CRC cells. Our findings indicate that CBP affects the hyperinduction of WNT activity by butyrate. ICG-001, which specifically blocks association between CBP and beta-catenin, abrogates the butyrate-triggered increase in the number of CRC cells with high levels of WNT/catenin signaling. Combination treatment of CRC cells with ICG-001 and butyrate results in cell type-specific effects on apoptosis. Further, both butyrate and ICG-001 repress CRC cell proliferation, with additive effects in suppressing cell growth. Our study strongly suggests that ICG-001-like agents would be effective against butyrate/HDACi-resistant CRC cells. Therefore, ICG-001-like agents may represent an important therapeutic option for CRCs that exhibit low-fold hyperactivation of WNT activity and apoptosis in the presence of HDACis. The findings generated from this study may lead to approaches that utilize modulation of CBP activity to facilitate CRC therapeutic or chemopreventive strategies.

Crosstalk between Wnt Signaling and RNA Processing in Colorectal Cancer

RNA processing involves a variety of processes affecting gene expression, including the removal of introns through RNA splicing, as well as 3' end processing (cleavage and polyadenylation). Alternative RNA processing is fundamentally important for gene regulation, and aberrant processing is associated with the initiation and progression of cancer. Deregulated Wnt signaling, which is the initiating event in the development of most cases of human colorectal cancer (CRC), has been linked to modified RNA processing, which may contribute to Wnt-mediated colonic carcinogenesis. Crosstalk between Wnt signaling and alternative RNA splicing with relevance to CRC includes effects on the expression of Rac1b, an alternatively spliced gene associated with tumorigenesis, which exhibits alternative RNA splicing that is influenced by Wnt activity. In addition, Tcf4, a crucial component of Wnt signaling, also exhibits alternative splicing, which is likely involved in colonic tumorigenesis. Modulation of 3' end formation, including of the Wnt target gene COX-2, also can influence the neoplastic process, with implications for CRC. While many human genes are dependent on introns and splicing for normal levels of gene expression, naturally intronless genes exist with a unique metabolism that allows for intron-independent gene expression. Effects of Wnt activity on the RNA metabolism of the intronless Wnt-target gene c-jun is a likely contributor to cancer development. Further, butyrate, a breakdown product of dietary fiber and a histone deacetylase inhibitor, upregulates Wnt activity in CRC cells, and also modulates RNA processing; therefore, the interplay between Wnt activity, the modulation of this activity by butyrate, and differential RNA metabolism in colonic cells can significantly influence tumorigenesis. Determining the role played by altered RNA processing in Wnt-mediated neoplasia may lead to novel interventions aimed at restoring normal RNA metabolism for therapeutic benefit. Therefore, this minireview presents a brief overview of several aspects of RNA processing of relevance to cancer, which potentially influence, or are influenced by, Wnt signaling activity.

Tcf3 and cell cycle factors contribute to butyrate resistance in colorectal cancer cells

Butyrate, a fermentation product of dietary fiber, inhibits clonal growth in colorectal cancer (CRC) cells dependent upon the fold induction of Wnt activity. We have developed a CRC cell line (HCT-R) that, unlike its parental cell line, HCT-116, does not respond to butyrate exposure with hyperactivation of Wnt signaling and suppressed clonal growth. PCR array analyses revealed Wnt pathway-related genes, the expression of which differs between butyrate-sensitive HCT-116 CRC cells and their butyrate-resistant HCT-R cell counterparts. We identified overexpression of Tcf3 as being partially responsible for the butyrate-resistant phenotype, as this DNA-binding protein suppresses the hyperinduction of Wnt activity by butyrate. Consequently, Tcf3 knockdown in HCT-R cells restores their sensitivity to the effects of butyrate on Wnt activity and clonal cell growth. Interestingly, the effects of overexpressed Tcf3 differ between HCT-116 and HCT-R cells; thus, in HCT-116 cells Tcf3 suppresses proliferation without rendering the cells resistant to butyrate. In HCT-R cells, however, the overexpression of Tcf3 inhibits Wnt activity, and the cells are still able to proliferate due to the higher expression levels of cell cycle factors, particularly those driving the G(1) to S transition. Knowledge of the molecular mechanisms determining the variable sensitivity of CRC cells to butyrate may assist in developing approaches that prevent or reverse butyrate resistance.

The Notch ligand Delta-like 1 integrates inputs from TGFbeta/Activin and Wnt pathways

Unlike the well-characterized nuclear function of the Notch intracellular domain, it has been difficult to identify a nuclear role for the ligands of Notch. Here we provide evidence for the nuclear function of the Notch ligand Delta-like 1 in colon cancer (CC) cells exposed to butyrate. We demonstrate that the intracellular domain of Delta-like 1 (Dll1icd) augments the activity of Wnt signaling-dependent reporters and that of the promoter of the connective tissue growth factor (CTGF) gene. Data suggest that Dll1icd upregulates CTGF promoter activity through both direct and indirect mechanisms. The direct mechanism is supported by co-immunoprecipitation of endogenous Smad2/3 proteins and Dll1 and by chromatin immunoprecipitation analyses that revealed the occupancy of Dll1icd on CTGF promoter sequences containing a Smad binding element. The indirect upregulation of CTGF expression by Dll1 is likely due to the ability of Dll1icd to increase Wnt signaling, a pathway that targets CTGF. CTGF expression is induced in butyrate-treated CC cells and results from clonal growth assays support a role for CTGF in the cell growth-suppressive role of butyrate. In conclusion, integration of the Notch, Wnt, and TGFbeta/Activin signaling pathways is in part mediated by the interactions of Dll1 with Smad2/3 and Tcf4.

Role of Wnt signaling in the development of type 2 diabetes

Type 2 diabetes is characterized by insulin resistance, insulin deficiency, and hyperglycemia. Susceptibility to type 2 diabetes has been linked to Wnt signaling, which plays an important role in intestinal tumorigenesis. Carriers of variants of the transcription factor 7-like 2 gene, an important component of the Wnt pathway, are at enhanced risk for developing type 2 diabetes. The modulation of proglucagon expression by Wnt activity may partially explain the link between Wnt signaling and diabetes, and one of the transcriptional and processing products of the proglucagon gene, the glucagon-like peptide-1 (GLP-1), exhibits a wide variety of antidiabetogenic activities. GLP-1 stimulates Wnt signaling in pancreatic beta cells, enhancing cell proliferation; thus, positive feedback between GLP-1 and Wnt signaling may result in increased proliferation, and suppressed apoptosis, of pancreatic cells. Since beta-cell protection is a potential treatment for type 2 diabetes, stimulation of Wnt activity may represent a valid therapeutic approach.

[Fiber, cancer stem cells, and the Wnt signaling continuum: possibilities for colorectal cancer prevention and therapeutics]

Wnt signaling is implicated in the initiation of human colorectal cancer (CRC). While the relationship between Wnt activity and proliferation is well known, studies have also shown an association between high levels of Wnt activity and apoptosis. Through analyses of ten human CRC cell lines, we have found that inhibitors of histone deacetylases (HDACis), such as butyrate, promote apoptosis of CRC cells through hyper-induction of Wnt signalingû thus, hyper-activation of Wnt activity by HDACis may represent a novel preventive and therapeutic strategy against CRC. Our findings may explain why studies on the protective role of dietary fiber and its product butyrate against CRC have yielded inconsistent findings. We believe that the variability in the levels of induced Wnt activity and apoptosis in CRC cells observed in vitro reflects the in vivo existence of CRC subtypes with variable degrees of responsiveness to butyrate. Given that Wnt activity has been linked to intestinal stem cell renewal and the migratory potential of CRC stem cells, this essay discussed the potential of modulation of Wnt signaling by HDACis as a therapeutic approach against CRC stem cells. Finally, we considered possible gene therapy approaches that target Wnt-positive CRC stem cells.

Butyrate and Wnt signaling: a possible solution to the puzzle of dietary fiber and colon cancer risk?

Studies on the protective role of dietary fiber and its breakdown product butyrate against colorectal cancer (CRC) have yielded inconsistent findings. We have reported that butyrate treatment of CRC cells in vitro modulates canonical Wnt signaling, a pathway which is constitutively activated in the majority of CRCs. Analyses of ten human CRC cell lines exposed to butyrate have established that the levels of apoptosis in these cells are dependent upon the fold induction of canonical Wnt transcriptional activity. It is likely that the observed variability in the levels of induced Wnt activity and apoptosis in CRC cells in vitro reflects the existence of different CRC subtypes in vivo. The existence of CRC subtypes, individual- and population-specific variation in butyrate producing colonic microflora, and the time at which the colorectal lesions (early vs. late stage) are exposed to fiber/butyrate are all factors that may influence the protective role of fiber against CRC. We discuss the evidence by which these factors influence the effects of fiber on colonic tumorigenesis and outline experimental approaches for testing these hypotheses.

The activation of beta-catenin by Wnt signaling mediates the effects of histone deacetylase inhibitors

Most colorectal carcinomas (CRCs) exhibit constitutively active Wnt signaling. We have reported that (a) the histone deacetylase inhibitor (HDACi)(2) sodium butyrate (NaB) modulates the canonical Wnt transcriptional activity of CRC cells in vitro and (b) a linear relationship exists between the increase in Wnt transcriptional activity and the levels of apoptosis in ten CRC cell lines treated with NaB. Herein we report that structurally different HDACis modulate Wnt signaling in CRC cells and a mechanism involved in this action is an increase in beta-catenin that is dephosphorylated at Ser-37 and Thr-41 residues. The increase of active (Ser-37 and Thr-41 dephosphorylated) beta-catenin in CRC cells treated with HDACis is initiated at the ligand level and the inhibition of this increase suppresses Wnt signaling and lowers the levels of apoptosis. CRC cells that develop resistance to the apoptotic effects of HDACis exhibit lower levels of active beta-catenin compared to apoptosis-sensitive parental cells and this resistance is reversed by increasing the levels of active beta-catenin. Results from comparative studies between HDACi-resistant and HDACi-sensitive cells suggest that non-histone targets of HDACis mediate the effects on Wnt signaling and apoptosis.

Modulation of Wnt-specific colon cancer cell kill by butyrate and lithium

Colorectal cancer (CRC) may be particularly amenable to gene therapy because CRCs exhibit constitutive upregulation of Wnt signaling. We have previously demonstrated that butyrate, found in the colonic lumen, modulates Wnt signaling and nonspecifically upregulates transcription from minimal promoters. Because both of these actions may influence the efficiency and specificity of Wnt-targeted expression, the effects of butyrate on Wnt-targeted gene therapy were determined. Lithium is another agent known to upregulate Wnt activity in HCT-116 CRC cells and therefore may induce Wnt-targeted CRC cell kill. CRC cells were cotransfected with an expression vector for green fluorescent protein (GFP) and different versions of vectors coupling Wnt-sensitive promoters to FADD or diphtheria toxin A-chain (DT) effector genes. Cells were treated with butyrate and/or lithium chloride and flow cytometry was used to determine the percentage of remaining transfected (GFP-positive) cells. We demonstrate that promoter and cell type-specific differences occur in Wnt-specific cell kill induced by FADD and DT. A Wnt-sensitive version of the CMV promoter (TcfCMV) exhibited the optimum combination of efficient SW620 CRC cell kill and Wnt specificity; in addition, treatment with a physiologically relevant concentration of butyrate enhanced cell kill induced by TcfCMV-FADD while maintaining specificity. In HCT-116 CRC cells, optimum results were achieved utilizing TcfFos-DT constructs and cotreatment with both butyrate and lithium. The findings suggest that effective CRC cell kill can be achieved by gene therapy through modulation of Wnt signaling by butyrate and/or lithium.

Linear relationship between Wnt activity levels and apoptosis in colorectal carcinoma cells exposed to butyrate

We have reported that butyrate, a fatty acid produced by dietary fiber that induces cell cycle arrest, differentiation and/or apoptosis in colorectal carcinoma (CRC) cells in vitro, modulates Wnt activity in 2 CRC cell lines (Bordonaro et al., Int. J. Cancer, 2002; 97:42-51). Our study determines how changes in the levels of Wnt activity induced by butyrate relate to the effects of butyrate on apoptosis, cell cycle arrest and differentiation of CRC cells. In 10 human CRC cell lines a direct relationship was shown between apoptosis and butyrate-induced increase in Wnt activity, as well as between suppressed clonal growth and increased Wnt activity. No correlation existed between butyrate-induced increase in Wnt activity and differentiation. The direct relationship between apoptosis and Wnt activity was supported by analyses of DLD-1 and HCT-116 cells expressing a dominant negative form of Tcf4, and therefore, with repressed Wnt activity, as well as by measuring the ratio of apoptotic to live cells in flow cytometry-sorted cell fractions with high and low Wnt activity. Novel flow cytometric methodology was utilized to show that butyrate differentially increases the number of cells with Wnt activity in different CRC cell lines. Thus, CRC cell lines in which butyrate upregulated Wnt activity to relatively high levels were most susceptible to the apoptotic effects of butyrate, whereas cell lines in which butyrate modestly modulated Wnt activity were less affected.

Pharmacological and genetic modulation of Wnt-targeted Cre-Lox-mediated gene expression in colorectal cancer cells

Wnt-targeted gene therapy has been proposed as a treatment for human colorectal cancer (CRC). The Cre-Lox system consists of methodology for enhancing targeted expression from tissue-specific or cancer-specific promoters. We analyzed the efficiency of Wnt-specific promoters as drivers of the Cre-mediated activity of a luciferase reporter gene or cell death effector gene in CRC cell lines in the presence and absence of two modulators of Wnt activity, sodium butyrate and lithium chloride. Butyrate is present in the colonic lumen after digestion of fiber-rich foods, whereas the colonic lumen is readily accessible to lithium chloride. In both SW620 and HCT-116 CRC cells, a physiologically relevant concentration of butyrate upregulated reporter and effector activity and altered the Wnt-specific expression pattern. Lithium chloride markedly enhanced Cre-Lox-mediated Wnt-specific reporter expression only in APC wild-type CRC cells. Possibilities for genetic modulation of the proposed CRC therapy included Wnt-specific expression of a floxed Lef1-VP16 fusion that enhanced Wnt-specific cell death and of a floxed dominant-negative Tcf4 that specifically downregulated endogenous Wnt activity. These findings demonstrated that the Cre-Lox system, in combination with pharmacological and genetic modulators, represents effective methodology for enhancing Wnt-targeted gene therapy.

Cell type- and promoter-dependent modulation of the Wnt signaling pathway by sodium butyrate

The Wnt signaling pathway modulates the transcription of genes linked to proliferation, differentiation and tumor progression. beta-Catenin-Tcf (BCT)-dependent Wnt signaling is influenced by the short-chain fatty acid sodium butyrate, which induces growth arrest and/or maturation of colonic carcinoma cells. We have compared the effects of sodium butyrate on BCT-dependent signaling in 2 colon carcinoma cell lines that differ in their physiologic response to butyrate, with SW620 cells responding to butyrate by undergoing terminal differentiation and apoptosis, and HCT-116 cells undergoing reversible growth arrest, but no significant apoptotic cell death. Furthermore, these colon carcinoma cell lines differ in their mechanism of Wnt pathway activation, with adenomatous polyposis coli (APC) mutant SW620 cells having high levels of BCT complexes and APC wild-type HCT-116 cells having mutant beta-catenin, low levels of BCT complexes and correspondingly higher levels of free Tcf. We have demonstrated that in SW620 cells, butyrate downregulates BCT-dependent expression of the Tcf-TK, matrilysin and cyclin D1 promoters, whereas in HCT-116 cells, butyrate upregulates expression of these promoters. Cotransfection with expression vectors that interfere with the Wnt pathway suggests that butyrate enhances BCT complex-DNA binding. Butyrate reduces the expression of Tcf4 in HCT-116 cells, consistent with the induction by butyrate of Tcf-repressible promoters in these cells. These findings indicate that sodium butyrate modulates the Wnt pathway in SW620 and HCT-116 cells in a different manner and that these differences have consequences for promoter activity that may influence the physiologic response to butyrate.

Transcriptional regulation of the vitamin D(3) receptor gene by ZEB

The hormone 1,25-dihydroxyvitamin D(3) influences the growth and differentiation of a number of cell types. The functions of 1,25-dihydroxyvitamin D(3) are mediated through the vitamin D(3) receptor (VDR); therefore, an understanding of the regulation of VDR expression is important when considering the molecular mechanisms of differentiation induced by vitamin D(3) and its analogues. ZEB, a Krüppel-type transcription factor known to repress the transcription of several genes, binds to two sites within the VDR promoter and activates the transcription of this receptor in a cell-specific manner. Transfection of ZEB into SW620 colon carcinoma cells results in an up-regulation of the expression of endogenous VDR, confirming the role of ZEB in the transcriptional activation of the VDR gene. The expression of VDR is also induced by c-MYB; thus, ZEB and c-MYB may modulate the levels of VDR expression during differentiation in embryonal development, as well as in cancer cells.

Down-regulation of beta-catenin TCF signaling is linked to colonic epithelial cell differentiation

The beta-catenin TCF pathway is implicated in the regulation of colonic epithelial cell proliferation, but its role in the regulation of cell differentiation is unknown. The colon carcinoma cell line, Caco-2, spontaneously undergoes G(0)/G(1) cell cycle arrest and differentiates along the absorptive cell lineage over 21 days in culture. In parallel, we show that beta-catenin-TCF activity and complex formation are significantly down-regulated. The down-regulation of beta-catenin-TCF signaling was independent of APC, which we characterized as having a nonsense mutation in codon 1367 in Caco-2 cells, but was associated with a decrease in TCF-4 protein levels. Total beta-catenin levels increased during Caco-2 cell differentiation, although this was attributable to an increase in the membrane, E-cadherin-associated, fraction of beta-catenin. Importantly, down-regulation of beta-catenin-TCF signaling in undifferentiated Caco-2 cells by three different mechanisms, ectopic expression of E-cadherin, wild-type APC, or dominant negative TCF-4, resulted in an increase in the promoter activities of two genes that are well-established markers of cell differentiation, alkaline phosphatase and intestinal fatty acid binding protein. These studies demonstrate, therefore, that in addition to its established role in the regulation of cell proliferation, down-regulation of the beta-catenin-TCF pathway is associated with the promotion of a more-differentiated phenotype in colonic epithelial cells.

Cellular mechanisms of risk and transformation

Our early work using the first array and imaging methods for the quantitative analysis of the expression of 4000 cDNA sequences suggested that modulation of mitochondrial gene expression was a factor in determining whether colonic epithelial cells displayed a differentiated or transformed phenotype. We have since dissected a pathway in which mitochondrial function is a key element in determining the probability of cells undergoing cell-cycle arrest, lineage-specific differentiation, and cell death. Moreover, this pathway is linked to signaling through beta-catenin-Tcf, but in a manner that is independent of effects of the APC gene on beta-catenin-Tcf activity. Utilization of unique mouse genetic models of intestinal tumorigenesis has confirmed that mitochondrial function is an important element in generation of apoptotic cells in the colon in vivo and has demonstrated that modulation of cell death may be involved in intestinal tumor progression rather than initiation. Normal spatial and temporal patterns of cell proliferation, differentiation, and apoptosis in the colonic mucosa are determined by developmentally programmed genetic signals and external signals generated by homo- and heterotypic cell interactions, humoral agents, and lumenal contents. Mitochondrial function may play a pivotal role in integrating these signals and in determining probability of cells entering different maturation pathways. How this is accomplished is under investigation using high-density cDNA microarrays.