Colorectal carcinomas in mice lacking the catalytic subunit of PI(3)Kgamma

Targeting PI3K/Akt signal transduction for cancer therapy

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway plays a crucial role in various cellular processes and is aberrantly activated in cancers, contributing to the occurrence and progression of tumors. Examining the upstream and downstream nodes of this pathway could allow full elucidation of its function. Based on accumulating evidence, strategies targeting major components of the pathway might provide new insights for cancer drug discovery. Researchers have explored the use of some inhibitors targeting this pathway to block survival pathways. However, because oncogenic PI3K pathway activation occurs through various mechanisms, the clinical efficacies of these inhibitors are limited. Moreover, pathway activation is accompanied by the development of therapeutic resistance. Therefore, strategies involving pathway inhibitors and other cancer treatments in combination might solve the therapeutic dilemma. In this review, we discuss the roles of the PI3K/Akt pathway in various cancer phenotypes, review the current statuses of different PI3K/Akt inhibitors, and introduce combination therapies consisting of signaling inhibitors and conventional cancer therapies. The information presented herein suggests that cascading inhibitors of the PI3K/Akt signaling pathway, either alone or in combination with other therapies, are the most effective treatment strategy for cancer.

Disease-related mutations in PI3Kγ disrupt regulatory C-terminal dynamics and reveal a path to selective inhibitors

Class I Phosphoinositide 3-kinases (PI3Ks) are master regulators of cellular functions, with the class IB PI3K catalytic subunit (p110γ) playing key roles in immune signalling. p110γ is a key factor in inflammatory diseases and has been identified as a therapeutic target for cancers due to its immunomodulatory role. Using a combined biochemical/biophysical approach, we have revealed insight into regulation of kinase activity, specifically defining how immunodeficiency and oncogenic mutations of R1021 in the C-terminus can inactivate or activate enzyme activity. Screening of inhibitors using HDX-MS revealed that activation loop-binding inhibitors induce allosteric conformational changes that mimic those in the R1021C mutant. Structural analysis of advanced PI3K inhibitors in clinical development revealed novel binding pockets that can be exploited for further therapeutic development. Overall, this work provides unique insights into regulatory mechanisms that control PI3Kγ kinase activity and shows a framework for the design of PI3K isoform and mutant selective inhibitors.

Frontline Science: Coincidental null mutation of Csf2rα in a colony of PI3Kγ-/- mice causes alveolar macrophage deficiency and fatal respiratory viral infection

PI3Ks have been identified as key signaling proteins involved in many basic biologic processes in health and disease. Transgenic animals have been essential tools to study the underlying molecular mechanisms in this context and therefore, have been widely used to elucidate the role of these factors in many different settings. More specifically, PI3Kγ, a subunit highly expressed in the hematopoietic system, has been implicated to play an important role in many inflammatory diseases as well as cancer. Here, we report identification of multiple, additional, previously unknown mutations in the genome of a widely used PI3Kγ-deficient (PI3Kγ^-/-) mouse colony. These include a STOP mutation in the GM-CSFRα chain, leading to a complete and specific deficiency in GM-CSF signaling. PI3Kγ^-/- animals consequently lacked alveolar macrophages (AMs) and succumbed rapidly to influenza virus infection. Furthermore, PI3Kγ^-/- mice carried an additional mutation that affects mucin 2 (Muc2) transcripts. This protein is strongly involved in the regulation of colorectal cancer, and indeed, conflicting reports have indicated that PI3Kγ^-/- animals spontaneously develop colorectal tumors. Thus, we uncover previously unknown, confounding factors present in a strain of PI3Kγ^-/- mice, leading to additional deficiencies in important signaling pathways with potentially wide-ranging implications for the interpretation of previous studies. By separating the mutations, we established a unique Csf2ra^-/- mouse model that allows us to study the role of cell intrinsic GM-CSFR signaling in vivo without confounding variables introduced by defective IL-5R and IL-3R signaling in mice lacking the common β chain (Csf2rb).

Advances in subunits of PI3K class I in cancer

Phosphatidylinositol 3-kinases (PI3Ks) include members of a unique and conserved family of intracellular lipid kinases that phosphorylate the 3-hydroxyl group of phosphatidylinositols and phosphoinositides. The resultant activation of many intracellular signalling pathways regulates various biological functions such as cell metabolism, survival, growth, proliferation, polarity, and apoptosis. PI3Ks are classified into three types: class I, II, and III. Of them, class I PI3K is most widely studied and plays an important role in the development and progression of tumours. In this review, we describe PI3K family members and their functions, especially the subunits of class I PI3K, their alterations in cancers, as well as PI3K inhibitors and their clinical trial status in cancer-targeted therapy.

Targeting p110gamma in gastrointestinal cancers: attack on multiple fronts

Phosphoinositide 3-kinases (PI3Ks) regulate several cellular functions that are critical for cancer progression and development, including cell survival, proliferation and migration. Three classes of PI3Ks exist with the class I PI3K encompassing four isoforms of the catalytic subunit known as p110α, p110β, p110γ, and p110δ. Although for many years attention has been mainly focused on p110α recent evidence supports the conclusion that p110β, p110γ, and p110δ can also have a role in cancer. Amongst these, accumulating evidence now indicates that p110γ is involved in several cellular processes associated with cancer and indeed this specific isoform has emerged as a novel important player in cancer progression. Studies from our laboratory have identified a specific overexpression of p110γ in human pancreatic ductal adenocarcinoma (PDAC) and in hepatocellular carcinoma (HCC) tissues compared to their normal counterparts. Our data have further established that selective inhibition of p110γ is able to block PDAC and HCC cell proliferation, strongly suggesting that pharmacological inhibition of this enzyme can directly affect growth of these tumors. Furthermore, increasing evidence suggests that p110γ plays also a key role in the interactions between cancer cells and tumor microenvironment and in particular in tumor-associated immune response. It has also been reported that p110γ can regulate invasion of myeloid cells into tumors and tumor angiogenesis. Finally p110γ has also been directly involved in regulation of cancer cell migration. Taken together these data indicate that p110γ plays multiple roles in regulation of several processes that are critical for tumor progression and metastasis. This review will discuss the role of p110γ in gastrointestinal tumor development and progression and how targeting this enzyme might represent a way to target very aggressive tumors such as pancreatic and liver cancer on multiple fronts.

Comprehensive identification of mutational cancer driver genes across 12 tumor types

With the ability to fully sequence tumor genomes/exomes, the quest for cancer driver genes can now be undertaken in an unbiased manner. However, obtaining a complete catalog of cancer genes is difficult due to the heterogeneous molecular nature of the disease and the limitations of available computational methods. Here we show that the combination of complementary methods allows identifying a comprehensive and reliable list of cancer driver genes. We provide a list of 291 high-confidence cancer driver genes acting on 3,205 tumors from 12 different cancer types. Among those genes, some have not been previously identified as cancer drivers and 16 have clear preference to sustain mutations in one specific tumor type. The novel driver candidates complement our current picture of the emergence of these diseases. In summary, the catalog of driver genes and the methodology presented here open new avenues to better understand the mechanisms of tumorigenesis.

FOXO3 expression during colorectal cancer progression: biomarker potential reflects a tumour suppressor role

BACKGROUND

In previous studies, the Forkhead/winged-helix-box-class-O3 (FOXO3) transcription factor has displayed both tumour suppressive and metastasis-promoting properties.To clarify its role in human colorectal cancer (CRC) progression, we examined in vivo FOXO3 expression at key points of the metastatic cascade.

METHODS

Formalin-fixed paraffin-embedded resection specimens from normal colon, adenomas, primary CRC specimens of different pathological stage and CRC specimens with matched liver metastases were used to generate three separate custom-designed tissue microarray (TMA) representations of metastatic progression. Triplicate cores, immunostained for FOXO3 were scored semiquantitatively by two investigators.

RESULTS

The FOXO3 expression is significantly reduced in CRC specimens compared with normal tissue, and progressive FOXO3 downregulation is associated with advancing pathological stage. In addition, recurrent stage I/II primary tumours show a significantly lower FOXO3 expression compared with stage-matched non-recurrent tumours. When stratified according to high and low FOXO3 expression, mean disease-free survival in the low-expressing group was 28 months (95% CI 15.8-50.6) compared with 64 months (95% CI 52.9-75.4) in the high-expressing group.

CONCLUSION

We have demonstrated an association between low FOXO3 expression and CRC progression in vivo using purpose-designed TMAs. Forkhead/winged-helix-box-class-O3 may represent a novel biomarker of nodal and distant disease spread with clinical utility in CRC.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

Identification of upregulated phosphoinositide 3-kinase γ as a target to suppress breast cancer cell migration and invasion

Metastasis is the major cause of breast cancer mortality. We recently reported that aberrant G-protein coupled receptor (GPCR) signaling promotes breast cancer metastasis by enhancing cancer cell migration and invasion. Phosphatidylinositol 3-kinase γ (PI3Kγ) is specifically activated by GPCRs. The goal of the present study was to determine the role of PI3Kγ in breast cancer cell migration and invasion. Immunohistochemical staining showed that the expression of PI3Kγ protein was significantly increased in invasive human breast carcinoma when compared to adjacent benign breast tissue or ductal carcinoma in situ. PI3Kγ was also detected in metastatic breast cancer cells, but not in normal breast epithelial cell line or in non-metastatic breast cancer cells. In contrast, PI3K isoforms α, β and δ were ubiquitously expressed in these cell lines. Overexpression of recombinant PI3Kγ enhanced the metastatic ability of non-metastatic breast cancer cells. Conversely, migration and invasion of metastatic breast cancer cells were inhibited by a PI3Kγ inhibitor or by siRNA knockdown of PI3Kγ but not by inhibitors or siRNAs of PI3Kα or PI3Kβ. Lamellipodia formation is a key step in cancer metastasis, and PI3Kγ blockade disrupted lamellipodia formation induced by the activation of GPCRs such as CXC chemokine receptor 4 and protease-activated receptor 1, but not by the epidermal growth factor tyrosine kinase receptor. Taken together, these results indicate that upregulated PI3Kγ conveys the metastatic signal initiated by GPCRs in breast cancer cells, and suggest that PI3Kγ may be a novel therapeutic target for development of chemotherapeutic agents to prevent breast cancer metastasis.

Adenomatous polyposis coli regulates oligodendroglial development

The expression of the gut tumor suppressor gene adenomatous polyposis coli (Apc) and its role in the oligodendroglial lineage are poorly understood. We found that immunoreactive APC is transiently induced in the oligodendroglial lineage during both normal myelination and remyelination following toxin-induced, genetic, or autoimmune demyelination murine models. Using the Cre/loxP system to conditionally ablate APC from the oligodendroglial lineage, we determined that APC enhances proliferation of oligodendroglial progenitor cells (OPCs) and is essential for oligodendrocyte differentiation in a cell-autonomous manner. Biallelic Apc disruption caused translocation of β-catenin into the nucleus and upregulated β-catenin-mediated Wnt signaling in early postnatal but not adult oligodendroglial lineage cells. The results of conditional ablation of Apc or Ctnnb1 (the gene encoding β-catenin) and of simultaneous conditional ablation of Apc and Ctnnb1 revealed that β-catenin is dispensable for postnatal oligodendroglial differentiation, that Apc one-allele deficiency is not sufficient to dysregulate β-catenin-mediated Wnt signaling in oligodendroglial lineage cells, and that APC regulates oligodendrocyte differentiation through β-catenin-independent, as well as β-catenin-dependent, mechanisms. Gene ontology analysis of microarray data suggested that the β-catenin-independent mechanism involves APC regulation of the cytoskeleton, a result compatible with established APC functions in neural precursors and with our observation that Apc-deleted OPCs develop fewer, shorter processes in vivo. Together, our data support the hypothesis that APC regulates oligodendrocyte differentiation through both β-catenin-dependent and additional β-catenin-independent mechanisms.

Inhibition of PI3K signaling spurs new therapeutic opportunities in inflammatory/autoimmune diseases and hematological malignancies

The phosphoinositide 3-kinase/mammalian target of rapamycin/protein kinase B (PI3K/mTOR/Akt) signaling pathway is central to a plethora of cellular mechanisms in a wide variety of cells including leukocytes. Perturbation of this signaling cascade is implicated in inflammatory and autoimmune disorders as well as hematological malignancies. Proteins within the PI3K/mTOR/Akt pathway therefore represent attractive targets for therapeutic intervention. There has been a remarkable evolution of PI3K inhibitors in the past 20 years from the early chemical tool compounds to drugs that are showing promise as anticancer agents in clinical trials. The use of animal models and pharmacological tools has expanded our knowledge about the contribution of individual class I PI3K isoforms to immune cell function. In addition, class II and III PI3K isoforms are emerging as nonredundant regulators of immune cell signaling revealing potentially novel targets for disease treatment. Further complexity is added to the PI3K/mTOR/Akt pathway by a number of novel signaling inputs and feedback mechanisms. These can present either caveats or opportunities for novel drug targets. Here, we consider recent advances in 1) our understanding of the contribution of individual PI3K isoforms to immune cell function and their relevance to inflammatory/autoimmune diseases as well as lymphoma and 2) development of small molecules with which to inhibit the PI3K pathway. We also consider whether manipulating other proximal elements of the PI3K signaling cascade (such as class II and III PI3Ks or lipid phosphatases) are likely to be successful in fighting off different immune diseases.

The determinants of head and neck cancer: Unmasking the PI3K pathway mutations

Studies attempting to identify and understand the function of mutated genes and deregulated molecular pathways in cancer have been ongoing for many years. The PI3K-PTEN-mTOR signaling pathway is one of the most frequently deregulated pathways in cancer. PIK3CA mutations are found 11%-33% of head and neck cancer (HNC). The hotspot mutation sites for PIK3CA are E542K, E545K and H1047R/L. The PTEN somatic mutations are in 9-23% of HNC, and they frequently cluster in the phosphatase domain of PTEN protein. PTEN loss of heterozygosity (LOH) ranges from 41%-71% and loss of PTEN protein expression occurs in 31.2% of the HNC samples. PIK3CA and PTEN are key molecules in the PI3K-PTEN-mTOR signaling pathway. In this review, we provided a comprehensive overview of mutations in the PI3K-PTEN-mTOR molecular circuitry in HNC, including PI3K family members, TSC1/TSC2, PTEN, AKT, and mTORC1 and mTORC2 complexes. We discussed how these genetic alterations may affect protein structure and function. We also highlight the latest discoveries in protein kinase and tumor suppressor families, emphasizing how mutations in these families interfere with PI3K signaling. A better understanding of the mechanisms underlying cancer formation, progression and resistance to therapy will inform selection of novel genomic-based personalized therapies for head and neck cancer patients.

Studies on the expression patterns of class I PI3K catalytic subunits and its prognostic significance in colorectal cancer

The phosphatidylinositol 3-kinase/AKT (PI3K/AKT) pathway plays a critical role in human cancer. We determined the expression patterns of class I PI3K catalytic subunits and evaluated their importance in the development or progression of colorectal cancer (CRC). For this purpose, expression of class I PI3K isoforms was evaluated in 82 primary CRC and paired non-cancerous mucosa samples by qRT-PCR. P-AKT-Ser473 and P-AKT-Thr308 expression were measured by western blot. We found that, compared with paired non-cancerous mucosa samples, mRNA expression of p110α and p110β in CRCs was significantly increased to 2.02-fold (95% confidence interval [CI] 1.25-3.28 fold) and 1.76-fold (95% CI 1.19-2.60 fold), respectively; while slight differences were found regarding the expression of p110δ (0.57-fold; 95% CI 0.31-1.07 fold) and p110γ (0.97-fold; 95% CI 0.50-1.88 fold). Increased p110α and p110β expression correlated with primary tumor size, regional lymph node metastases, and AJCC stage. Increased p110β expression also correlated with distant metastasis. P-AKT-Thr308 and P-AKT-Ser473 expression showed significant direct correlations with p110α and p110β mRNA expression. Besides, CRC patients with p110β mRNA overexpression had a worse disease-free survival after radical surgery compared with those with normal or decreased levels (P = 0.043). It was, therefore, concluded that the altered p110α and p110β expression might contribute to the CRC development or progression.

Synergism between altered cortical polarity and the PI3K/TOR pathway in the suppression of tumour growth

Loss of function of pins (partner of inscuteable) partially disrupts neuroblast (NB) polarity and asymmetric division, results in fewer and smaller NBs and inhibits Drosophila larval brain growth. Food deprivation also inhibits growth. However, we find that the combination of loss of function of pins and dietary restriction results in loss of NB asymmetry, overproliferation of Miranda-expressing cells, brain overgrowth and increased frequency of tumour growth on allograft transplantation. The same effects are observed in well-fed pins larvae that are mutant for pi3k (phosphatidylinositol 3-kinase) or exposed to the TOR inhibitor rapamycin. Thus, pathways that are sensitive to food deprivation and dependent on PI3K and TOR are essential to suppress tumour growth in Drosophila larval brains with compromised pins function. These results highlight an unexpected crosstalk whereby the normally growth-promoting, nutrient-sensing PI3K/TOR pathway suppresses tumour formation in neural stem cells with compromised cell polarity.

Phosphoinositide 3-kinaseγ controls the intracellular localization of CpG to limit DNA-PKcs-dependent IL-10 production in macrophages

Synthetic oligodeoxynucleotides containing unmethylated CpG motifs (CpG) stimulate innate immune responses. Phosphoinositide 3-kinase (PI3K) has been implicated in CpG-induced immune activation; however, its precise role has not yet been clarified. CpG-induced production of IL-10 was dramatically increased in macrophages deficient in PI3Kγ (p110γ(-/-)). By contrast, LPS-induced production of IL-10 was unchanged in the cells. CpG-induced, but not LPS-induced, IL-10 production was almost completely abolished in SCID mice having mutations in DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Furthermore, wortmannin, an inhibitor of DNA-PKcs, completely inhibited CpG-induced IL-10 production, both in wild type and p110γ(-/-) cells. Microscopic analyses revealed that CpG preferentially localized with DNA-PKcs in p110γ(-/-) cells than in wild type cells. In addition, CpG was preferentially co-localized with the acidic lysosomal marker, LysoTracker, in p110γ(-/-) cells, and with an early endosome marker, EEA1, in wild type cells. Over-expression of p110γ in Cos7 cells resulted in decreased acidification of CpG containing endosome. A similar effect was reproduced using kinase-dead mutants, but not with a ras-binding site mutant, of p110γ. Thus, it is likely that p110γ, in a manner independent of its kinase activity, inhibits the acidification of CpG-containing endosomes. It is considered that increased acidification of CpG-containing endosomes in p110γ(-/-) cells enforces endosomal escape of CpG, which results in increased association of CpG with DNA-PKcs to up-regulate IL-10 production in macrophages.

A sensitized RNA interference screen identifies a novel role for the PI3K p110γ isoform in medulloblastoma cell proliferation and chemoresistance

Medulloblastoma is the most common malignant brain tumor in children and is associated with a poor outcome. We were interested in gaining further insight into the potential of targeting the human kinome as a novel approach to sensitize medulloblastoma to chemotherapeutic agents. A library of small interfering RNA (siRNA) was used to downregulate the known human protein and lipid kinases in medulloblastoma cell lines. The analysis of cell proliferation, in the presence or absence of a low dose of cisplatin after siRNA transfection, identified new protein and lipid kinases involved in medulloblastoma chemoresistance. PLK1 (polo-like kinase 1) was identified as a kinase involved in proliferation in medulloblastoma cell lines. Moreover, a set of 6 genes comprising ATR, LYK5, MPP2, PIK3CG, PIK4CA, and WNK4 were identified as contributing to both cell proliferation and resistance to cisplatin treatment in medulloblastoma cells. An analysis of the expression of the 6 target genes in primary medulloblastoma tumor samples and cell lines revealed overexpression of LYK5 and PIK3CG. The results of the siRNA screen were validated by target inhibition with specific pharmacological inhibitors. A pharmacological inhibitor of p110γ (encoded by PIK3CG) impaired cell proliferation in medulloblastoma cell lines and sensitized the cells to cisplatin treatment. Together, our data show that the p110γ phosphoinositide 3-kinase isoform is a novel target for combinatorial therapies in medulloblastoma.

The p110α and p110β isoforms of class I phosphatidylinositol 3-kinase are involved in toll-like receptor 5 signaling in epithelial cells

BACKGROUND

Bacterial flagellin triggers inflammation in mammalian cells via Toll-like receptor (TLR) 5. Release of the chemokine IL-8 in response to flagellin involves NF-κB, p38 MAP kinase, and phosphatidylinositol 3-kinase (PI3K). However, PI3K has been reported to be either pro- or anti-inflammatory in different model systems. We hypothesized that this could be due to different activities of the p110α and β isoforms of PI3K.

RESULTS

PI3K and Akt were rapidly activated in Caco-2 colon carcinoma cells by flagellin. Using a plasmid-based shRNA delivery system and novel p110 isoform-specific inhibitors, we found that flagellin-induced IL-8 production was dependent on both p110α and p110β. However in the mouse, inhibition of p110β but not p110α reduced the increase of serum IL-6 levels induced by intraperitoneal injection of flagellin.

CONCLUSIONS

These data demonstrate that the p110α and β isoforms of class IA PI3K are both required for the proinflammatory response to flagellin.

Prioritization of driver mutations in pancreatic cancer using cancer-specific high-throughput annotation of somatic mutations (CHASM)

Over 20,000 genes were recently sequenced in a series of 24 pancreatic cancers. We applied CHASM (Cancer-specific High-throughput Annotation of Somatic Mutations) to 963 of the missense somatic missense mutations discovered in these 24 cancers. CHASM identified putative driver mutations (false discovery rate ≤0.3) in three known pancreatic cancer driver genes (P53, SMAD4, CDKN2A). An additional 15 genes with putative driver mutations include genes coding for kinases (PIK3CG, DGKA, STK33, TTK and PRKCG), for cell cycle related proteins (NEK8), and for proteins involved in cell adhesion (CMAS, PCDHB2). These and other mutations identified by CHASM point to potential "driver genes" in pancreatic cancer that should be prioritized for additional follow-up.

Role of phosphoinositide 3-kinase {alpha}, protein kinase C, and L-type Ca2+ channels in mediating the complex actions of angiotensin II on mouse cardiac contractility

Although angiotensin II (Ang II) plays an important role in heart disease associated with pump dysfunction, its direct effects on cardiac pump function remain controversial. We found that after Ang II infusion, the developed pressure and +dP/dt(max) in isolated Langendorff-perfused mouse hearts showed a complex temporal response, with a rapid transient decrease followed by an increase above baseline. Similar time-dependent changes in cell shortening and L-type Ca(2+) currents were observed in isolated ventricular myocytes. Previous studies have established that Ang II signaling involves phosphoinositide 3-kinases (PI3K). Dominant-negative inhibition of PI3Kalpha in the myocardium selectively eliminated the rapid negative inotropic action of Ang II (inhibited by approximately 90%), whereas the loss of PI3Kgamma had no effect on the response to Ang II. Consistent with a link between PI3Kalpha and protein kinase C (PKC), PKC inhibition (with GF 109203X) reduced the negative inotropic effects of Ang II by approximately 50%. Although PI3Kalpha and PKC activities are associated with glycogen synthase kinase-3beta and NADPH oxidase, genetic ablation of either glycogen synthase kinase-3beta or p47(phox) (an essential subunit of NOX2-NADPH oxidase) had no effect on the inotropic actions of Ang II. Our results establish that Ang II has complex temporal effects on contractility and L-type Ca(2+) channels in normal mouse myocardium, with the negative inotropic effects requiring PI3Kalpha and PKC activities.

Targeting PI3K in neuroblastoma

PURPOSE

This work employs pharmacological targeting of phosphoinositide 3-kinases (PI3K) in selected neuroblastoma (NB) tumors with the inhibitor AS605240, which has been shown to express low toxicity and relative specificity for the PI3K species γ.

METHODS

The expression pattern of PI3K isoforms in 7 NB cell lines and 14 tumor patient samples was determined by Western blotting and immunocytochemistry. The effect of AS605240 on the growth of four selected tumor cell lines was assessed. Two cell lines exhibiting (SK-N-LO) or lacking (SK-N-AS) PI3Kγ expression were chosen for further in vitro analysis, which involved propidium iodide (PI)-based cell cycle staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL-staining) of apoptotic cells and analysis of PI3K/Akt-related signaling pathways via Western blotting and translocation experiments. The action of AS605240 in vivo was addressed by xenograft experiments in severe combined immunodeficiency (SCID) mice, thereby comparing SK-N-LO and SK-N-AS derived tumors. Apoptosis induced in SK-N-LO tumors was shown by immunohistochemical TUNEL-staining.

RESULTS

Significant expression of PI3Kγ in neuroblastoma patient biopsies and tumor cell lines was detected. AS605240 induced apoptosis in NB cell lines proportional to this expression and suppressed growth of PI3Kγ positive, but not negative, tumors in a xenograft mouse model. No adverse effects of the inhibitor treatment were observed.

CONCLUSIONS

Our observations hint to an oncogenic function of PI3Kγ in distinct neuroblastoma entities and reveal PI3K targeting by AS605240 as a promising molecular therapy of these tumors.

ESCI award lecture: from a little mouse to rationale medicine for bone loss

Completion of the human genome is one of the many significant milestones in the new era of systems biology. The current phase of genomic studies is focused upon parsing this new found genetic data with respect to scientific interest, and economic and health impact applications. As the sequences are now available and whole genome single nucleotide polymorphism maps for multiple human diseases will be available with the advent of modern genomics, the big challenge is to determine the function of these genes in the context of the entire organism. The emphasis is therefore on functional genomic analysis that represents the new front-line and limiting factor for realizing potential benefits of genome-based science. Defined gene targeting has been proven to be particularly useful as loss of expression mutants can reveal essential functions of molecules and the pathogenesis of disease. Using gene-targeted mice, my group has over the years identified genes that control heart and lung functions; apoptosis; lymphocyte activation; cancer; pain; diabetes; fertility or wound healing . In this study, I would like to review our work on RANKL in more detail.

Akt as a therapeutic target in cancer

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors.

OBJECTIVE

This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells.

METHODS

We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular.

RESULTS/CONCLUSIONS

The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.

The transforming functions of PI3-kinase-gamma are linked to disruption of intercellular adhesion and promotion of cancer cell invasion

The involvement of phosphoinositide 3-kinases class IA (PI3K-alpha and -beta) in cancer cell proliferation, survival, motility, and invasiveness is now well established. However, the possible contribution of the class IB PI3Kgamma in cancer cell transformation remains to be explored. In this study, we have stably transfected the PI3Kgamma-deficient human colon cancer cell line HCT8/S11 with expression vectors encoding either wild-type PI3Kgamma, its plasma membrane targeted form CAAX-PI3Kgamma, or the PI3Kgamma lipid and protein kinase-dead mutant (CAAX-K832R). We provide evidence that the constitutively active CAAX-PI3Kgamma variant induced collagen type I invasion in HCT8/S11 cells through disruption of cell-cell adhesion, with no apparent impact on cell proliferation and motility. The proinvasive activity of CAAX-PI3K-gamma was abolished by pharmacological inhibitors targeting PI3-K activities (wortmannin), Rho-GTPases, and the Rho-Rho kinase axis (C3T exoenzyme and Y27632, respectively). Conversely, the wild-type PI3Kgamma and its double mutant CAAX-K832R were ineffective on cancer cell invasion measured under control or stimulated conditions operated with the proinvasive agents leptin and intestinal trefoil factor. Taken together, our data indicate that PI3Kgamma exerts transforming functions via several mechanisms in human colon epithelial cancer cells, including alterations of homotypic cell-cell adhesion and induction of collagen type I invasion through canonical proinvasive pathways.

CD28 provides T-cell costimulation and enhances PI3K activity at the immune synapse independently of its capacity to interact with the p85/p110 heterodimer

Activation of PI3K is among the earliest signaling events observed in T cells after conjugate formation with antigen-presenting cells (APCs). The relevant PI3K catalytic isoform and relative contribution of the TcR and CD28 to PI3K activity at the immune synapse have not been determined unequivocally. Using a quantitative imaging-based assay, we show that the PI3K activity at the T cell–APC contact area is dependent on the p110δ, but not the p110γ, isoform of PI3K. CD28 enhanced PIP3 production at the T-cell synapse independently of its YMNM PI3K-recruitment motif that instead was required for efficient PKCθ recruitment. CD28 could partially compensate for the lack of p110δ activity during T-cell activation, which indicates that CD28 and p110δ act in parallel and complementary pathways to activate T cells. Consistent with this, CD28 and p110δ double-deficient mice were severely immune compromised. We therefore suggest that combined pharmaceutic targeting of p110δ activity and CD28 costimulation has potent therapeutic potential.

Activation of the serine/threonine protein kinase AKT during the progression of colorectal neoplasia

BACKGROUND

AKT has been identified as a major regulator of cell proliferation, tumorigenesis, and apoptosis. In this study, we evaluated changes in the activity of AKT during colorectal cancer (CRC) progression.

MATERIALS AND METHODS

We used stage-oriented human CRC tissue microarrays, including 99 invasive carcinomas, 28 tubular adenomas, and 18 samples of normal colonic mucosa. The tissue array slides were stained with a mouse monoclonal antiphospho-AKT antibody using the avidin-biotin complex method.

RESULTS

Activation of AKT was detected mostly in the invasive carcinomas. Sixty-three percent of carcinomas demonstrated strong to moderate AKT activity. Seven percent of carcinomas were phospho-AKT (p-AKT) negative, and 30% (30 of 99) were p-AKT weakly positive. Conversely, 78% of normal colonic mucosas were p-AKT negative, and only 4 samples stained weakly for p-AKT. Eighty-two percent of adenomas were weakly positive for p-AKT, 1 was p-AKT negative, and none exhibited strong or moderate p-AKT stain. At a significance level of .05, we found that the distribution of p-AKT stain scores for cancer was shifted to the right of adenoma (P < .0001) and normal (P < .0001) and for adenoma was shifted to the right of normal (P < .0001). AKT activation did not correlate with tumor stage (P = .28), lymph node metastasis (P = .45), lymphatic invasion (P = .46), or distant metastasis (P = .34).

CONCLUSION

This study shows increasing activation of AKT during CRC progression. This finding suggests a role of p-AKT in colorectal carcinogenesis and provides a rationale for using p-AKT inhibitor API-2/triciribine, which is currently under clinical investigation for the treatment of CRC.

Insulin-like growth factor-1 and PTEN deletion enhance cardiac L-type Ca2+ currents via increased PI3Kalpha/PKB signaling

Ca2+ influx through the L-type Ca2+ channel (I(Ca,L)) is a key determinant of cardiac contractility and is modulated by multiple signaling pathways. Because the regulation of I(Ca,L) by phosphoinositide-3-kinases (PI3Ks) and phosphoinositide-3-phosphatase (PTEN) is unknown, despite their involvement in the regulation of myocardial growth and contractility, I(Ca,L) was recorded in myocytes isolated from mice overexpressing a dominant-negative p110alpha mutant (DN-p110alpha) in the heart, lacking the PI3Kgamma gene (PI3Kgamma(-/-)) or with muscle-specific ablation of PTEN (PTEN(-/-)). Combinations of these genetically altered mice were also examined. Although there were no differences in the expression level of CaV1.2 proteins, basal I(Ca,L) densities were larger (P<0.01) in PTEN(-/-) myocytes compared with littermate controls, PI3Kgamma(-/-), or DN-p110alpha myocytes and showed negative shifts in voltage dependence of current activation. The I(Ca,L) differences seen in PTEN(-/-) mice were eliminated by pharmacological inhibition of either PI3Ks or protein kinase B (PKB) as well as in PTEN(-/-)/DN-p110alpha double mutant mice but not in PTEN(-/-)/PI3Kgamma(-/-) mice. On the other hand, application of insulin-like growth factor-1 (IGF-1), an activator of PKB, increased I(Ca,L) in control and PI3Kgamma(-/-), while having no effects on I(Ca,L) in DN-p110alpha or PTEN(-/-) mice. The I(Ca,L) increases induced by IGF-1 were abolished by PKB inhibition. Our results demonstrate that IGF-1 treatment or inactivation of PTEN enhances I(Ca,L) via PI3Kalpha-dependent increase in PKB activation.

BCR-ABL Regulates Phosphatidylinositol 3-Kinase-p110γ Transcription and Activation and Is Required for Proliferation and Drug Resistance

The BCR-ABL oncogene is the hallmark of chronic myeloid leukemia, a clonal hematopoietic stem cell disorder. BCR-ABL displays constitutive tyrosine kinase activity, required for its transformation ability. Although the molecular mechanisms behind this malignancy are not fully understood, a role for phosphatidylinositol (PI) 3-kinase has been repeatedly described. Here we report the specific up-regulation of the class I(B) catalytic subunit of PI 3-kinase (p110gamma) in response to BCR-ABL expression. We demonstrate that this upregulation is due to increased transcription and is dependent on both PI 3-kinase and MEK activity. We performed in vitro kinase activity assays and show that BCR-ABL also leads to increased p110gamma activity and that this activation requires both G protein-coupled receptor and Ras signaling. In addition, by transfection of cells with dominant negative p110gamma, we determined that this specific PI 3-kinase isoform is involved in both proliferation and the apoptosis resistance associated with chronic myeloid leukemia. The data presented here define for the first time the ability of BCR-ABL to alter the expression levels of PI 3-kinase isoforms and also demonstrate a previously unreported link between BCR-ABL and p110gamma.

Membrane rafts segregate pro- from anti-apoptotic insulin-like growth factor-I receptor signaling in colon carcinoma cells stimulated by members of the tumor necrosis factor superfamily

In the tumor microenvironment, autocrine/paracrine loops of insulin-like growth factors (IGFs) contribute to cancer cell survival. However, we report here that IGF-I can send contradictory signals that interfere with cell death induced by different ligands of the tumor necrosis factor (TNF) superfamily. IGF-I protected human colon carcinoma cells from TNF-alpha-induced apoptosis, but it enhanced the apoptotic response to anti-Fas antibody and TNF-related apoptosis inducing ligand stimulation. This proapoptotic effect of IGF-I, observed in several but not all tested colon cancer cell lines, was mediated via the phosphatidylinositol 3'-kinase (PI3K)/Akt pathway. Furthermore, IGF-I receptors (IGF-IR) were located in and out of membrane lipid rafts and were tyrosine autophosphorylated in response to IGF-I. However, disruption of rafts by acute cholesterol depletion shifted IGF-IR to non-raft domains, abolished the IGF-I-mediated proapoptotic effect, and inhibited the IGF-I-dependent IRS-1 and Akt recruitment into and phosphorylation/activation within lipid rafts. Replenishing cell membranes with cholesterol reversed these effects. Activation of extracellular-regulated kinase-1/2 and p38 mitogen-activated protein kinase, which convey the IGF-I anti-apoptotic effect, occurred independently of lipid rafts. Thus, we propose that segregation of IGF-IR in and out of lipid rafts may dynamically regulate the pro- and anti-apoptotic effects of IGF-I on apoptosis induced by TNF superfamily members.

Enhanced v-Src-induced oncogenic transformation in the absence of focal adhesion kinase is mediated by phosphatidylinositol 3-kinase

We showed previously [K. Moissoglu, I.H. Gelman, J. Biol. Chem. 278 (2003) 47946-47959] that oncogenic v-Src could induce 7- to 10-fold greater anchorage-independent growth (AIG) in FAK-null mouse embryo fibroblasts (MEF) compared to those expressing FAK. Here, we demonstrate that the enhanced AIG (eAIG) correlates with increased activation levels of phosphatidylinositol 3-kinase (PI3K) and not with changes in the protein levels of the p85 regulatory subunit of PI3K, PDK1 or PTEN- modulators, and/or mediators of PI3K activity. eAIG could be blunted selectively by treatment with the PI3K inhibitor, LY294002, or by overexpression of either the PI3K antagonist, PTEN, dominant-interfering alleles of PI3K or a downstream PI3K mediator, AKT, but not by the MEK inhibitor, PD98059, dominant-interfering alleles of MEK or the signal transducer and activator of transcription (STAT)-3. In contrast, RNAi-mediated knockdown of FAK resulted in increased v-Src-induced AIG. Expression of a constitutively active PI3K allele was sufficient to induce higher levels of AIG, whereas overexpression of v-Src produced only larger-sized colonies in soft agar. Interestingly, FAK was required for full activation of PI3K by PDGF whereas the activation of PI3K by insulin was significantly increased in FAK-/- cells. Thus, although FAK is dispensable for v-Src-induced oncogenic transformation in vitro, it may exert either positive or negative effects on signaling or motility depending on which pathways are activated in cancer cells.

Gene targeting: attention to detail

When it comes to silencing genes in mice, not all approaches are equal. An example published in this issue of Cell (Patrucco et al., 2004) suggests that caution should be used when validating potential drug targets by genetic disruption.

Crossregulation of NF-kappaB by the APC/GSK-3beta/beta-catenin pathway

Glycogen synthase kinase-3beta (GSK-3beta) and adenomatous polyposis coli (APC) play an important role in the regulation of beta-catenin. Inhibition of or defects in their functions can lead to activation of beta-catenin. beta-catenin has been recently found to interact with and inhibit nuclear factor kappa B (NF-kappaB). However, the regulatory roles of GSK-3beta/APC on the NF-kappaB signaling pathway are unknown because of their diverse effects. In this study, we investigated whether GSK-3beta/APC might regulate NF-kappaB activity through beta-catenin. We found that inhibition of GSK-3beta suppressed NF-kappaB activity, whereas reexpression of APC restored NF-kappaB activity in APC mutated cells. The regulatory effects were through beta-catenin because depletion of beta-catenin with small interfering RNA (siRNA) in the same systems reversed the effects. The regulatory relationship was further supported by the analysis of primary breast tumor tissues in vivo in which NF-kappaB target TRAF1 was inversely correlated with activated beta-catenin. Thus, APC/GSK-3beta, through beta-catenin, may crossregulate NF-kappaB signaling pathway.

Chromatin immunoprecipitation microarrays for identification of genes silenced by histone H3 lysine 9 methylation

Switching from acetylation to methylation at histone H3 lysine 9 (K9) has recently been shown to contribute to euchromatin gene silencing. To identify genes silenced by K9 modifications, we probed a human CpG island microarray with DNA obtained by chromatin immunoprecipitation (ChIP) in a cancer cell line using an anti-H3-K9 methylated antibody or an anti-H3-K9 acetylated antibody. Of the 27 clones with the highest signal ratio of K9 methylation over acetylation (Me/Ac), 13 contained repetitive sequences. Among 14 nonrepetitive clones, we identified 11 genes (seven known and four previously undescribed), one EST, and two unknown fragments. Using ChIP-PCR, all 18 examined clones showed higher ratios of H3-K9 Me/Ac than the active gene control, P21, thus confirming the microarray data. In addition, we found a strong correlation between the K9 Me/Ac ratio and CpG island DNA methylation (R = 0.92, P < 0.01), and five of seven genes examined (megalin, thrombospondin-4, KR18, latrophilin-3, and phosphatidylinositol-3-OH kinase P101 subunit) showed lack of expression by RT-PCR and reactivation by DNA methylation and/or histone deacetylase inhibition, suggesting that these genes are true targets of silencing through histone modifications. All five genes also showed significant DNA methylation in a cell line panel and in primary colon cancers. Our data suggest that CpG island microarray coupled with ChIP can identify novel targets of gene silencing in cancer. This unbiased approach confirms the tight coupling between DNA methylation and histone modifications in cancer and could be used to probe gene silencing in nonneoplastic conditions as well.

Preclinical models for chemoprevention of colon cancer

Colon cancer is the second leading cause of cancer incidence and death in the USA in 2002. Specific genetic defects have been identified which cause hereditary colon cancers in humans. In addition, a number of intestinal luminal risk factors for colon cancer have been described. This information has been exploited to develop experimental cell and rodent models which recapitulate features of human colon cancer. In this chapter, we will discuss the strengths and limitations of these models to further our understanding of basic mechanisms of colon carcinogenesis and to develop strategies for colon cancer chemoprevention.

The role of chemokines and chemokine receptors in eosinophil activation during inflammatory allergic reactions

Chemokines are important chemotactic cytokines that play a fundamental role in the trafficking of leukocytes to sites of inflammation. They are also potent cell-activating factors, inducing cytokine and histamine release and free radical production, a fact that makes them particularly important in the pathogenesis of allergic inflammation. The action of chemokines is regulated at the level of agonist production and processing as well as at the level of receptor expression and coupling. Therefore, an analysis of the ligands must necessarily consider receptors. Eosinophils are target cells involved in the allergic inflammatory response since they are able to release a wide variety of mediators including CC and CXC chemokines and express their receptors. These mediators could damage the airway epithelial cells and might be important to stimulate other cells inducing an amplification of the allergic response. This review focuses on recently emerging data pertaining to the importance of chemokines and chemokine receptors in promoting eosinophil activation and migration during the allergic inflammatory process. The analysis of the function of eosinophils and their chemokine receptors during allergic inflammation might be a good approach to understanding the determinants of asthma severity and to developing novel therapies.

Role of phosphoinositide 3-kinase signaling in mast cells: new insights from knockout mouse studies

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases essential for diverse physiological reactions. In recent years a series of gene-targeted mice lacking different types of PI3Ks and related molecules have been generated which enable us to understand the role of PI3K pathways, particularly class I members, in vivo. Analyses of such gene-targeted mice have led to major discoveries in the physiological roles of PI3K signaling in mast cell biology. In particular the role of PI3Ks has been extensively studied in signaling through the high-affinity IgE receptor (FcepsilonRI), since mast cells are the main effector cells in type I allergic reaction associated with IgE-dependent mechanisms. Furthermore, the knockout mice have provided significant information concerning the role of PI3K signals in mast cell differentiation. This review presents several new insights into mast cell biology, which have been elucidated by the analyses of these knockout mice.

Gene-targeting reveals physiological roles and complex regulation of the phosphoinositide 3-kinases

Phosphoinositide 3-kinases (PI3Ks) are represented by a family of eight distinct enzymes that can be divided into three classes based on their structure and function. The class I PI3Ks are heterodimeric enzymes that are regulated by recruitment to plasma membrane following receptor activation and which control numerous cellular functions, including growth, differentiation, migration, survival, and metabolism. New light has been shed on the biological role of individual members of the class I PI3Ks and their regulatory subunits through gene-targeting experiments. In addition, these experiments have brought the complexity of how PI3K activation is regulated into focus.

Mechanism by which cAMP activates PI3-kinase and increases bile acid secretion in WIF-B9 cells

Previous studies in rat bile canalicular membrane vesicles and WIF-B9 cells revealed that cAMP-induced trafficking of ATP-binding cassette (ABC) transporters to the canalicular membrane and their activation require phosphoinositide 3-kinase (PI3-K) products. In the present studies, canalicular secretion of fluorescein isothiocyanate-glycocholate in WIF-B9 cells was increased by cAMP and a decapeptide that enhances PI3-K activity; these effects were inhibited by wortmannin. To determine the mechanism(s) whereby cAMP activates PI3-K, we examined signal transduction pathways in WIF-B9 and COS-7 cells. cAMP activated PI3-K in both cell lines in a phosphotyrosine-independent manner. PI3-K activity increased in association with p110 beta in both cell lines. The effect of cAMP was KT-5720 sensitive, suggesting involvement of protein kinase A. Expression of a dominant-negative beta-adrenergic receptor kinase COOH terminus (beta-ARKct), which blocks G beta gamma signaling, decreased PI3-K activation in both cell lines. cAMP increased GTP-bound Ras in COS-7 but not WIF-B9 cells. Expression of dominant-negative Ras abolished cAMP-mediated PI3-K, which suggests that the effect is downstream of Ras and G beta gamma. These data indicate that cAMP activates PI3-K in a cell type-specific manner and provide insight regarding mechanisms of PI3-K activation required for bile acid secretion.

Pharmacologic unmasking of epigenetically silenced tumor suppressor genes in esophageal squamous cell carcinoma

We performed a comprehensive survey of commonly inactivated tumor suppressor genes in esophageal squamous cell carcinoma (ESCC) based on functional reactivation of epigenetically silenced tumor suppressor genes by 5-aza-2'-deoxycytidine and trichostatin A using microarrays containing 12599 genes. Among 58 genes identified by this approach, 44 (76%) harbored dense CpG islands in the promoter regions. Thirteen of twenty-two tested gene promoters were methylated in cell lines, and ten in primary ESCC accompanied by silencing at the mRNA level. Potent growth suppressive activity of three genes including CRIP-1, Apolipoprotein D, and Neuromedin U in ESCC cells was demonstrated by colony focus assays. Pharmacologic reversal of epigenetic silencing is a powerful approach for comprehensive identification of tumor suppressor genes in human cancers.

beta-catenin interacts with and inhibits NF-kappa B in human colon and breast cancer

beta-catenin plays an important role in development and homeostasis. Deregulated beta-catenin is involved in oncogenesis. In this study, we found that beta-catenin can physically complex with NF-kappa B, resulting in a reduction of NF-kappa B DNA binding, transactivation activity, and target gene expression. Repressed NF-kappa B activity is found in human colon cancer cells in which beta-catenin is activated. Importantly, activated beta-catenin was found to inhibit the expression of NF-kappa B target genes, including Fas and TRAF1. Furthermore, a strong inverse correlation was identified between the expression levels of beta-catenin and Fas in colon and breast tumor tissues, suggesting that beta-catenin regulates NF-kappa B and its targets in vivo. Thus, beta-catenin may play an important role in oncogenesis through the crossregulation of NF-kappa B.

PTEN and TNF-alpha regulation of the intestinal-specific Cdx-2 homeobox gene through a PI3K, PKB/Akt, and NF-kappaB-dependent pathway

BACKGROUND & AIMS

PTEN (phosphatase and tensin homologue deleted from chromosome 10) is a dual-specificity phosphatase implicated in embryonic development, intestinal cell proliferation and differentiation, and tumor suppression. The transcription factor Cdx-2 is critical in intestinal development and homeostasis, and its expression is altered in colorectal cancers. However, the regulation of the Cdx-2 gene has not been entirely elucidated. Here, we hypothesize that Cdx-2 may be a target of PTEN signaling in the intestine.

METHODS

The expression patterns for Cdx-2 and PTEN along wild-type mouse colon, as well as in colon tumors occurring in Pten(+/-) mice, were examined. The effect of PTEN or phosphatidylinositol 3-kinase inhibition and tumor necrosis factor alpha on Cdx-2 messenger RNA and protein expression, Cdx-2 DNA binding activity, and the promoter activity of the Cdx-2 gene was analyzed in human colon cancer cell lines.

RESULTS

Cdx-2 expression correlates with PTEN along the length of the murine colon and in colonic polyps that develop in Pten(+/-) mice. In colon cancer cells, PTEN stimulates Cdx-2 protein expression and the transcriptional activity of the Cdx-2 promoter. Phosphatidylinositol 3-kinase inhibition by wortmannin or by a dominant-negative phosphatidylinositol 3-kinase mimics the Cdx-2 stimulation by PTEN. Inversely, cell treatment by tumor necrosis factor alpha decreases Cdx-2 expression. Phosphatidylinositol 3-kinase inhibition by PTEN or wortmannin has an inverse effect compared with tumor necrosis factor alpha on the balance between the p50 and p65 subunits of nuclear factor kappaB. p65 inhibits the activity of the Cdx-2 promoter, whereas p50 prevents p65 action.

CONCLUSIONS

Our results suggest that the intestinal Cdx-2 homeobox gene is a target of PTEN/phosphatidylinositol 3-kinase signaling and tumor necrosis factor alpha signaling via nuclear factor kappaB-dependent pathways.

Targeted expression of oncogenic K-ras in intestinal epithelium causes spontaneous tumorigenesis in mice

BACKGROUND & AIMS

Ras oncoproteins are mutated in about 50% of human colorectal cancers, but their precise role in tumor initiation or progression is still unclear.

METHODS

This study presents transgenic mice that express K-ras(V12G), the most frequent oncogenic mutation in human tumors, under control of the murine villin promoter in epithelial cells of the large and small intestine.

RESULTS

More than 80% of the transgenic animals displayed single or multiple intestinal lesions, ranging from aberrant crypt foci (ACF) to invasive adenocarcinomas. Expression of K-ras(V12G) caused activation of the MAP kinase cascade, and the tumors were frequently characterized by deregulated cellular proliferation. Unexpectedly, we obtained no evidence of inactivating mutations of the tumor suppressor gene Apc, the "gatekeeper" in colonic epithelial proliferation. However, spontaneous mutation of the tumor-suppressor gene p53, a frequent feature in the human disease, was found in 3 of 7 tumors that were tested.

CONCLUSIONS

This animal model recapitulates the stages of tumor progression as well as a part of the genetic alterations found in human colorectal cancer. Furthermore, it indicates that activation of K-ras in concert with mutations in p53 may constitute a route to digestive tumor formation and growth, underlining the fact that the pathway to intestinal cancer is not necessarily a single road.

Cross signaling, cell specificity, and physiology

The literature on intracellular signal transduction presents a confusing picture: every regulatory factor appears to be regulated by all signal transduction cascades and to regulate all cell processes. This contrasts with the known exquisite specificity of action of extracellular signals in different cell types in vivo. The confusion of the in vitro literature is shown to arise from several causes: the inevitable artifacts inherent in reductionism, the arguments used to establish causal effect relationships, the use of less than adequate models (cell lines, transfections, acellular systems, etc.), and the implicit assumption that networks of regulations are universal whereas they are in fact cell and stage specific. Cell specificity results from the existence in any cell type of a unique set of proteins and their isoforms at each level of signal transduction cascades, from the space structure of their components, from their combinatorial logic at each level, from the presence of modulators of signal transduction proteins and of modulators of modulators, from the time structure of extracellular signals and of their transduction, and from quantitative differences of expression of similar sets of factors.

Global and specific translational control by rapamycin in T cells uncovered by microarrays and proteomics

Rapamycin has been shown to affect translation. We have utilized two complementary approaches to identify genes that are predominantly affected by rapamycin in Jurkat T cells. One was to compare levels of polysome-bound and total RNA using oligonucleotide microarrays complementary to 6,300 human genes. Another was to determine protein synthesis levels using two-dimensional PAGE. Analysis of expression changes at the polysome-bound RNA levels showed that translation of most of the expressed genes was partially reduced following rapamycin treatment. However, translation of 136 genes (6% of the expressed genes) was totally inhibited. This group included genes encoding RNA-binding proteins and several proteasome subunit members. Translation of a set of 159 genes (7%) was largely unaffected by rapamycin treatment. These genes included transcription factors, kinases, phosphatases, and members of the RAS superfamily. Analysis of [(35)S]methionine-labeled proteins from the same cell populations using two-dimensional PAGE showed that the integrated intensity of 111 of 830 protein spots changed in rapamycin-treated cells by at least 3-fold (70 increased, 41 decreased). We identified 22 affected protein spots representing protein products of 16 genes. The combined microarray and proteomic approach has uncovered novel genes affected by rapamycin that may be involved in its immunosuppressive effect and other genes that are not affected at the level of translation in a context of general inhibition of cap-dependent translation.

Association and regulation of casein kinase 2 activity by adenomatous polyposis coli protein

Mutations in the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis coli and also sporadic colorectal cancer development. By using antibodies raised against the N-terminal region of APC protein, we have detected the variable masses of endogenous APC proteins in individual cell lines established from human colorectal carcinomas caused by nonsense mutations of the gene. Phosphorylation of immunoprecipitates of full-length and truncated APC were observed in in vitro kinase reaction, indicating association of APC with protein kinase activity. The kinase activity complexed with APC was sensitive to heparin and used GTP as phosphoryl donor, suggesting an involvement of casein kinase 2 (CK2). Both CK2alpha- and beta-subunits were found to associate with APC in immunoprecipitates as well as in pull-down assays, with preferential interaction of APC with tetrameric CK2 holoenzyme. In synchronized cell populations, the association of APC with CK2 was cell cycle dependent, with the highest association in G(2)/M. Unexpectedly, APC immunoprecipitates containing full-length APC protein inhibited CK2 in vitro, whereas immunoprecipitates of truncated APC had little effect. This was confirmed by using recombinant APC, and the inhibitory region was localized to the C terminus of APC between residues 2086 and 2394. Overexpression of this fragment in SW480 cells suppressed cell proliferation rates as well as tumorigenesis. These results demonstrate a previously uncharacterized functional interaction between the tumor suppressor protein APC and CK2 and suggest that growth-inhibitory effects of APC may be regulated by inhibition of CK2.