Genomic sequencing of DPC4 in the analysis of familial pancreatic carcinoma

Role of Heredity in Melanoma Susceptibility: A Primer for the Practicing Surgeon

Melanoma is a deadly skin cancer linked to ultraviolet radiation exposure. Heritable traits and sporadic mutations modify an individual's risk for melanoma that may be associated with phenotype. Familial/heritable melanomas are broadly used to describe families with an increased incidence of melanomas, although the underlying mutation may be unknown. Mutations associated with melanoma occur in cell cycle regulation, tumor suppression, chromosomal stability, DNA repair, pigmentation, and melanocyte differentiation genes. Genetic testing of individuals with a family history of melanoma may provide additional etiologic information and ensure patients with known markers for cancer development are closely monitored by physicians.

Immunohistochemistry, carcinomas of unknown primary, and incidence rates

Pathologists use immunohistochemistry is their day-to-day practices to assist in distinguishing site of origin of metastatic carcinomas. Here, the work-up is discussed neuroendocrine carcinomas, squamous cell carcinomas and adenocarcinomas with particular attention to tumor incident rates and predictive values of the best-performing immunohistochemical markers.

Development of bioluminescent chick chorioallantoic membrane (CAM) models for primary pancreatic cancer cells: a platform for drug testing

The aim of the present study was to develop chick-embryo chorioallantoic membrane (CAM) bioluminescent tumor models employing low passage cell cultures obtained from primary pancreatic ductal adenocarcinoma (PDAC) cells. Primary PDAC cells transduced with lentivirus expressing Firefly-luciferase (Fluc) were established and inoculated onto the CAM membrane, with >80% engraftment. Fluc signal reliably correlated with tumor growth. Tumor features were evaluated by immunohistochemistry and genetic analyses, including analysis of mutations and mRNA expression of PDAC pivotal genes, as well as microRNA (miRNA) profiling. These studies showed that CAM tumors had histopathological and genetic characteristic comparable to the original tumors. We subsequently tested the modulation of key miRNAs and the activity of gemcitabine and crizotinib on CAM tumors, showing that combination treatment resulted in 63% inhibition of tumor growth as compared to control (p < 0.01). These results were associated with reduced expression of miR-21 and increased expression of miR-155. Our study provides the first evidence that transduced primary PDAC cells can form tumors on the CAM, retaining several histopathological and (epi)genetic characteristics of original tumors. Moreover, our results support the use of these models for drug testing, providing insights on molecular mechanisms underlying antitumor activity of new drugs/combinations.

Selection criteria for genetic assessment of patients with familial melanoma

Approximately 5% to 10% of melanoma may be hereditary in nature, and about 2% of melanoma can be specifically attributed to pathogenic germline mutations in cyclin-dependent kinase inhibitor 2A (CDKN2A). To appropriately identify the small proportion of patients who benefit most from referral to a genetics specialist for consideration of genetic testing for CDKN2A, we have reviewed available published studies of CDKN2A mutation analysis in cohorts with invasive, cutaneous melanoma and found variability in the rate of CDKN2A mutations based on geography, ethnicity, and the type of study and eligibility criteria used. Except in regions of high melanoma incidence, such as Australia, we found higher rates of CDKN2A positivity in individuals with 3 or more primary invasive melanomas and/or families with at least one invasive melanoma and two or more other diagnoses of invasive melanoma and/or pancreatic cancer among first- or second-degree relatives on the same side of the family. The work summarized in this review should help identify individuals who are appropriate candidates for referral for genetic consultation and possible testing.

Expression of cell cycle-related molecules in biliary premalignant lesions: biliary intraepithelial neoplasia and biliary intraductal papillary neoplasm

Cholangiocarcinoma of intrahepatic and extrahepatic bile ducts has a multistep carcinogenesis. Two premalignant lesions have been suggested for invasive cholangiocarcinoma: biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct. How the carcinogenetic process differs between biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct is not clear. In this study, we performed a pathological study to reveal the expression of key molecules related to the cell cycle during 2 carcinogenetic lineages. We immunohistochemically examined the expression of p21, p53, cyclin D1, and Dpc4 in a total of 89 cases: nonneoplastic biliary epithelium, biliary intraepithelial neoplasia, intraductal papillary neoplasm of the bile duct, and invasive cholangiocarcinoma. The expression of p21, p53, and cyclin D1 was up-regulated with histological progression in both biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct, whereas Dpc4 expression was down-regulated in these 2 lineages. In biliary intraepithelial neoplasia, p21 expression was significantly up-regulated early on. In contrast, levels of all molecules changed gradually in intraductal papillary neoplasm of the bile duct. Changes in p53 expression during histological progression differed significantly between biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct. p53 expression was dramatically up-regulated at the invasive stage of biliary intraepithelial neoplasia, whereas it was quite low in noninvasive biliary intraepithelial neoplasia. In contrast, p53 expression was already up-regulated in low-grade intraductal papillary neoplasm and reached a plateau in high-grade intraductal papillary neoplasm and invasive cholangiocarcinoma. This study suggested p21, p53, cyclin D1, and Dpc4 to be involved in the carcinogenesis of both biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct. p53 expression was regulated differently in biliary intraepithelial neoplasia compared with intraductal papillary neoplasm of the bile duct.

Signal transduction pathway through activin receptors as a therapeutic target of musculoskeletal diseases and cancer

Activin, myostatin and other members of the TGF-beta superfamily signal through a combination of type II and type I receptors, both of which are transmembrane serine/threonine kinases. Activin type II receptors, ActRIIA and ActRIIB, are primary ligand binding receptors for activins, nodal, myostatin and GDF11. ActRIIs also bind a subset of bone morphogenetic proteins (BMPs). Type I receptors that form complexes with ActRIIs are dependent on ligands. In the case of activins and nodal, activin receptor-like kinases 4 and 7 (ALK4 and ALK7) are the authentic type I receptors. Myostatin and GDF11 utilize ALK5, although ALK4 could also be activated by these growth factors. ALK4, 5 and 7 are structurally and functionally similar and activate receptor-regulated Smads for TGF-beta, Smad2 and 3. BMPs signal through a combination of three type II receptors, BMPRII, ActRIIA, and ActRIIB and four type I receptors, ALK1, 2, 3, and 6. BMPs activate BMP-specific Smads, Smad1, 5 and 8. Smad proteins undergo multimerization with co-mediator Smad, Smad4, and translocated into the nucleus to regulate the transcription of target genes in cooperation with nuclear cofactors. The signal transduction pathway through activin type II receptors, ActRIIA and ActRIIB, with type I receptors is involved in various human diseases. In this review, we discuss the role of signaling through activin receptors as therapeutic targets of intractable neuromuscular diseases, endocrine disorders and cancers.

Bone morphogenetic protein signaling and growth suppression in colon cancer

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta superfamily, which utilize BMP receptors and intracellular SMADs to transduce their signals to regulate cell differentiation, proliferation, and apoptosis. Because mutations in BMP receptor type IA (BMPRIA) and SMAD4 are found in the germline of patients with the colon cancer predisposition syndrome juvenile polyposis, and because the contribution of BMP in colon cancers is largely unknown, we examined colon cancer cells and tissues for evidence of BMP signaling and determined its growth effects. We determined the presence and functionality of BMPR1A by examining BMP-induced phosphorylation and nuclear translocation of SMAD1; transcriptional activity via a BMP-specific luciferase reporter; and growth characteristics by cell cycle analysis, cell growth, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide metabolic assays. These assays were also performed after transfection with a dominant negative (DN) BMPR1A construct. In SMAD4-null SW480 cells, we examined BMP effects on cellular wound assays as well as BMP-induced transcription in the presence of transfected SMAD4. We also determined the expression of BMPR1A, BMP ligands, and phospho-SMAD1 in primary human colon cancer specimens. We found intact BMP signaling and modest growth suppression in HCT116 and two derivative cell lines and, surprisingly, growth suppression in SMAD4-null SW480 cells. BMP-induced SMAD signaling and BMPR1A-mediated growth suppression were reversed with DN BMPR1A transfection. BMP2 slowed wound closure, and transfection of SMAD4 into SW480 cells did not change BMP-specific transcriptional activity over controls due to receptor stimulation by endogenously produced ligand. We found no cell cycle alterations with BMP treatment in the HCT116 and derivative cell lines, but there was an increased G1 fraction in SW480 cells that was not due to increased p21 transcription. In human colon cancer specimens, BMP2 and BMP7 ligands, BMPRIA, and phospho-SMAD1 were expressed. In conclusion, BMP signaling is intact and growth suppressive in human colon cancer cells. In addition to SMADs, BMP may utilize SMAD4-independent pathways for growth suppression in colon cancers.

Disruption of transforming growth factor beta-Smad signaling pathway in head and neck squamous cell carcinoma as evidenced by mutations of SMAD2 and SMAD4

The role of the TGF-beta-Smad signaling pathway in the carcinogenesis of head and neck cancer has not been fully evaluated genetically. In this study, we screened for mutation in the five main members of the TGF-beta -Smad signaling pathway, TGF-beta type I receptor (TGFBRI), TGF-beta type II receptor (TGFBRII), SMAD2, SMAD3 and SMAD4, in eight human head and neck squamous cell carcinoma (HNSCC) cell lines. Two mutations with presumed loss of heterozygosity (LOH) were identified. A novel missense mutation of SMAD2, located in exon 8 at codon 276 TCG (ser) -->TTG (leu), was identified in cell line SCC-15. This is the first report of a biallelic mutation of the SMAD2 gene in HNSCC. A nonsense mutation of the SMAD4 gene in exon 5 codon 245 CAG (glut) -->TAG (stop) was found in cell line CAL27. Western blotting verified that this nonsense mutation gives rise to the complete loss of the Smad4 protein in the cells. While the down-regulation and loss of expressions of the TGF-beta-Smad signaling pathway have been described frequently in HNSCC, here we offer further genetic evidence that the pathway is directly targeted for mutation during the HNSCC tumorigenesis.

Effects of human papillomavirus type 16 E7 protein on the growth of cervical carcinoma cells and immuno-escape through the TGF-beta1 signaling pathway

OBJECTIVE

E7 is regarded as one of the main oncoproteins of high-risk human papillomaviruses (HPVs). It may affect the transforming growth factor beta 1 (TGF-beta1) signaling pathway. In this study, the relationship between HPV-16 infection and the functions of three critical factors of the TGF-beta1/Smads pathway was explored to assess the possible role of E7 in the development of cervical cancer.

METHODS

The expression of E7, TGF-beta1, TbetaR-II and Smad4 was detected by immunohistochemistry in paraffin-embedded cervical samples, and by RT-PCR and Western blotting in cervical cancer cell lines. The effect of TGF-beta1 on the growth of cervical cancer cells were tested by methyl thiazolyl tetrazolium (MTT), and the effects of HPV-16 E7 protein on normal and malignant cervical cells were investigated by flow cytometry.

RESULTS

During the progression from benign to malignant lesions, the expression levels of TGF-beta1 and Smad4 increased significantly in cervical carcinoma tissues. The expression of TGF-beta1 was positively correlated with E7 expression. In vitro experiments showed that TGF-beta1 could not inhibit the proliferation of several cervical carcinoma cell lines in long-term regulation, but could inhibit immunologic reactions of peripheral blood mononuclear cells (PBMCs). Blocking E7 expression could lower the expression level of TGF-beta1 and induce cells to enter apoptosis.

CONCLUSIONS

Our data indicate that HPV-16 E7 protein plays an important role during the development of cervical cancer by immuno-inhibition and stimulation of tumor cell proliferation through the TGF-beta1/Smads signaling pathway.

Functions and regulation of transforming growth factor-beta (TGF-β) in the prostate

The prostate is a highly androgen-dependent tissue that in humans exhibits marked susceptibility to carcinogenesis. The malignant epithelium generated from this tissue ultimately loses dependence on androgens despite retention or amplification of the androgen receptor. Accumulating evidence support that transforming growth factor-beta (TGF-beta) plays key roles in the control of androgen dependence and acquisition of resistance to such hormonal control. Although TGF-beta functions as a key tumour suppressor of the prostate, it can also promote malignant progression and metastasis of the advanced disease, through undefined mechanisms. In addition to giving an overview of the TGF-beta field as related to its function in prostate cancer, this Review focuses on novel findings that support the tumour suppressor function of TGF-beta is lost or altered by changes in the activity of the androgen receptor, insulin-like growth factor-I, Akt, and mTOR during malignant progression. Understanding the mechanisms of cross-talk between TGF-beta and such growth modulators has important implications for the rational therapeutics of prostate cancer.

Missense mutations of MADH4: characterization of the mutational hot spot and functional consequences in human tumors

PURPOSE AND EXPERIMENTAL DESIGN

The mutational spectrum of MADH4 (DPC4/SMAD4) opens valuable insights into the functions of this protein that confer its tumor-suppressive nature in human tumors. We present the MADH4 genetic status determined on a new set of pancreatic, biliary, and duodenal cancers with comparison to the mutational data reported for various tumor types.

RESULTS

Homozygous deletion, followed by inactivating nonsense or frameshift mutations, is the predominant form of MADH4 inactivation in pancreatic cancers. Among the naturally occurring MADH4 missense mutations, the MH2 domain is the most frequent target (77%) of missense mutations in human tumors. A mutational hot spot resides within the MH2 domain corresponding to codons 330 to 370, termed the mutation cluster region (MCR). A relationship was found between the locations of the missense mutations (the MH1 domain, the MH2-MCR, and the MH2 outside of the MCR) and the tumor types, suggesting environmental or selective influences in the development of MADH4 mutations. Immunohistochemical studies for Madh4 protein in nine archival cancers (six pancreatic cancers, two duodenal cancers, and one biliary cancer) with known missense mutations indicated that all mutations within the MH1 or MH2 domain COOH-terminal to the MCR (seven of nine cases) had negative or weak labeling, whereas two cancers with mutations within the MCR had strong positive nuclear labeling for Madh4 protein.

CONCLUSIONS

These findings have important implications for in vitro functional studies, suggesting that the majority of missense mutations inactivate Madh4 by protein degradation in contrast to those that occur within the MCR.

Regulation mechanisms of retinal pigment epithelial cell migration by the TGF-beta superfamily

PURPOSE

To investigate the expression of specific receptors, signal transducers and the effect of transforming growth factor-beta (TGF-beta) on retinal pigment epithelium (RPE) migration and proliferation.

METHODS

Human RPE cell line D407 was used in all experiments. The effect of TGF-beta on migration and proliferation were studied using a wound healing model and [3H]-thymidine incorporation, respectively. The expression of RNA related to the TGF-beta superfamily receptors and SMAD1-4 were assayed by reverse transcriptase-polymerase chain reaction (RT-CPR). The effects of TGF-beta on the intracellular position of SMAD were studied by immunoperoxidase and immunofluorescence.

RESULTS

Transforming growth factor-beta 4 nm and activin A 0.36 nm stimulated RPE migration. There was no effect on proliferation. RNA for TGF-beta receptors types 1 and 2, and SMAD1-4 were detected in RPE culture. Transforming growth factor-beta signal transducer SMAD2 but not SMAD1 moved from the cytoplasm to the nucleus after TGF-beta stimulation.

CONCLUSION

Transforming growth factor-beta can regulate RPE cell migration through specific signal transduction pathways.

Molecular diagnosis of early pancreatic ductal adenocarcinoma in high-risk patients

The prevalence of pancreatic cancer in the general population is too low--even in high-prevalence areas such as Northern Europe and North America (8-12 per 10(5) population)--relative to the diagnostic accuracy of present detection methods to permit primary screening in the asymptomatic adult population. The recognition that the lifetime risk of developing pancreatic cancer for patients with hereditary pancreatitis (HP) is extremely high (20% by the age of 60 years and 40% by the age of 70 years) poses considerable challenges and opportunities for secondary screening in those patients without any clinical features of pancreatic cancer. Even for secondary screening, the detection of cancer at a biological stage that would be amenable to cure by surgery (total pancreatectomy) still requires diagnostic modalities with a very high sensitivity and specificity. Conventional radiological imaging methods such as endoluminal ultrasound and endoscopic retrograde pancreatography, which have proved to be valuable in the early detection of early neoplastic lesions in patients with familial pancreatic cancer, may well be applicable to patients with HP but only in those without gross morphological features of chronic pancreatitis (other than parenchymal atrophy). Unfortunately, most cases of HP also have associated gross features of chronic pancreatitis that are likely to seriously undermine the diagnostic value of these conventional imaging modalities. Pre-malignant molecular changes can be detected in the pancreatic juice of patients. Thus, the application of molecular screening in patients with HP is potentially the most powerful method of detection of early pancreatic cancer. Although mutant (mt) K-ras can be detected in the pancreatic juice of most patients with pancreatic cancer, it is also present in patients with non-inherited chronic pancreatitis who do not progress to pancreatic cancer (at least in the short to medium term), as well as increasingly in the older population without pancreatic disease. Nevertheless, the presence of mt-K-ras may identify a genuinely higher-risk group, enabling additional diagnostic imaging and molecular resources to be focussed on such a group. What is clear is that prospective multi-centre studies, such as that being pursued by the European Registry of Hereditary Pancreatitis and Familial Pancreatic Cancer (EUROPAC), are essential for the development of an effective secondary screening programme for these patients.

Genetics of adenocarcinomas of the small intestine: frequent deletions at chromosome 18q and mutations of the SMAD4 gene

The small intestinal mucosa makes up about 90% of the total surface of the gastrointestinal tract. However, adenocarcinomas arise rarely in this location. To elucidate genetic alterations underlying tumour development in the small intestine we investigated 17 sporadic adenocarcinomas. By comparative genomic hybridization recurrent gains of chromosomal material were found at chromosomes 7, 8, 13q, and 20 (5/17, each), while non-random losses were seen at 8p, 17p (4/17, each), and 18 (8/17 cases). Deletions at 5q, the location of the APC tumour suppressor gene, were seen in three cases. Microsatellite analysis with markers on chromosomal arms 1p, 5q, 8p, 17p, 18q, 19p, and 22q revealed a microsatellite instable phenotype in two cases and a high frequency of loss at 18q21-q22 (80%). Given the high incidence of 18q21-q22 deletions, we performed sequencing analysis of SMAD4, a downstream component of the TGFbeta-pathway, located at 18q21. Four tumours displayed mutations in highly conserved domains of the gene indicating disruption of TGFbeta-signalling. Our data reveal complex genetic alterations in sporadic small intestinal carcinomas. However, most tumours share deletions of 18q21-q22, which frequently target SMAD4. This indicates that disruption of TGFbeta-signalling plays a critical role in small intestinal tumorigenesis.

SNO is a probable target for gene amplification at 3q26 in squamous-cell carcinomas of the esophagus

Amplification of the 3q26 region appears to occur frequently among esophageal squamous cell carcinomas (ESCs). We examined ESC cell lines for amplification and expression levels of four genes in this region: SNO and EVI1, which encode proteins antagonizing transforming growth factor-beta signaling, and two other putative target genes, TERC and PIK3CA. Amplification of SNO was accompanied by significant increases in its expression level, suggesting that this gene is activated in an amplification-dependent manner. SNO was also amplified in 5 of 44 primary ESCs (11.4%). However, expression levels of EVI1, TERC, and PIK3CA did not correlate with their copy-numbers, even though EVI1 and TERC showed the same amplification pattern as SNO. Taken together, the data suggest that of the four candidates, SNO is the most probable target in the 3q26 amplicon for involvement in the progression of ESC.

The role of genetic factors in the etiology of pancreatic adenocarcinoma: an update

Pancreatic cancer is a disease with a very poor prognosis and its etiology is still largely elusive. The only consistent environmental risk factor is cigarette smoking. A previous history of pancreatitis or diabetes mellitus is also considered to be a risk factor. Epidemiological studies have confirmed that relatives of those with pancreatic cancer have an increased risk of this malignancy, and it has been evaluated that 3-5% of all pancreatic cancer cases are caused by genetic predisposition to the disease. Usually this occurs in the setting of a known inherited cancer syndrome caused by mutations in genes such as BRCA1/2 and CDKN2A. Whether or not a true site-specific pancreatic adenocarcinoma syndrome exists is not known. The real challenge for the management of high risk patients is to develop new screening methods than can identify pre-neoplastic or early neoplastic lesions in a timely manner.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

Role of TGFbeta signaling in skin carcinogenesis

The TGFbeta signaling pathway is one of the most important mechanisms in the maintenance of epithelial homeostasis. Alterations leading to either the repression or enhancement of this pathway have been shown to affect cancer development. Although TGFbeta inhibits growth of normal epithelial cells, it is paradoxically overexpressed in many epithelial cancers. It has been postulated that TGFbeta acts as a tumor suppressor at the early stages of carcinogenesis, but overexpression of TGFbeta at late stages of carcinogenesis may be a critical factor for tumor invasion and metastasis. The detailed mechanisms regulating this functional switch of TGFbeta remain to be elucidated. The relevance of the TGFbeta signaling pathway to the development of primary epithelial tumors in man has been further substantiated by the discovery of mutations in TGFbeta receptors and in the downstream signaling mediators, the Smads. The epidermis is one of the major targeting tissues for TGFbeta signaling. Chemical carcinogenesis studies have revealed a paradoxical effect of TGFbeta on skin carcinogenesis: inhibition of papilloma formation but promotion of malignant conversion. In addition, deletion of the TGFbeta type II receptor accelerates skin carcinogenesis. This review focuses on our current understanding of the role of TGFbeta signaling in skin carcinogenesis.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

Smads mediate signaling of the TGFbeta superfamily in normal keratinocytes but are lost during skin chemical carcinogenesis

The Smads are the signaling mediators of the TGFbeta superfamily. In the present study, we examined Smad expression in mouse epidermis and chemically-induced skin tumors. Mutations in Smad2 and -4 genes were also screened. Transcripts of Smad1 through -5 were constantly expressed in the epidermis regardless of changes in TGFbeta signaling, state of differentiation and stages of carcinogenesis. Smad7 transcripts were barely detectable in keratinocytes, but were induced by TGFbeta1 treatment and in chemically-induced skin tumors. At the protein level, Smad1 was detected throughout the epidermis, whereas Smad2 through -5 exhibited greater levels in suprabasal layers than basal keratinocytes. In cultured keratinocytes, Smad2, -3 and -4 underwent nuclear translocation upon TGFbeta1 treatment. Furthermore, nuclear translocation of Smads correlated with decreased BrdU labeling in proliferative keratinocytes. Although no mutations were detected in the Smad2 and -4 genes in tumors, proteins of Smad1 through -5 were partially or completely lost in carcinomas. These data document that Smads are expressed at high levels in the epidermis and mediate signaling of the TGFbeta superfamily. During skin carcinogenesis, loss of Smad1 through -5 and overexpression of Smad7 may contribute to the loss of growth inhibition mediated by TGFbeta superfamily members, thus resulting in tumor progression.

The transforming growth factor-beta signaling pathway in tumorigenesis

Transforming growth factor-beta is believed to play a dual role in carcinogenesis. Through its ability to inhibit cellular proliferation it suppresses tumor development in its early stages, but in the course of tumor progression malignant cells often acquire resistance to growth inhibition by transforming growth factor-beta and themselves secrete large amounts of this cytokine. Transforming growth factor-beta furthers malignant progression in two ways: for one, it acts on nontransformed cells present in the tumor mass to suppress antitumor immune responses and to augment angiogenesis. Secondly, it promotes invasion and the formation of metastases in a cell-autonomous manner that requires transforming growth factor-beta signaling activity, albeit at reduced levels, to be present in the tumor cells themselves.

Dpc4 protein in mucinous cystic neoplasms of the pancreas: frequent loss of expression in invasive carcinomas suggests a role in genetic progression

DPC4 (MADH4, SMAD4) is a nuclear transcription factor shown to be genetically inactivated in over half of infiltrating ductal adenocarcinomas of the pancreas. Immunohistochemical labeling for the DPC4 gene product using a monoclonal antibody has recently been shown to be an extremely sensitive and specific marker for DPC4 gene alterations in pancreatic adenocarcinomas. Mucinous cystic neoplasms (MCNs) are a biologically less aggressive subtype of pancreatic neoplasm that may show benign, borderline, or overtly malignant features. However, the role of DPC4 inactivation in the development of MCNs has not been examined. The immunohistochemical expression of Dpc4 protein was therefore examined in 36 mucinous cystic neoplasms using this previously characterized monoclonal antibody. The 36 mucinous cystic neoplasms studied included 23 adenomas, 1 tumor with borderline potential, 5 tumors with carcinoma in situ, and 7 invasive carcinomas. Twenty-nine (100%) of the 29 noninvasive mucinous cystic neoplasms strongly expressed Dpc4 in the neoplastic epithelium. In striking contrast, only one (14%) of seven infiltrating carcinomas expressed Dpc4 in the neoplastic epithelium (p = 0.0001). The adjacent stroma retained expression of this protein in all 36 cases. In invasive MCNs with loss of Dpc4 expression, areas of carcinoma in situ were identified in the same paraffin sections, and these areas of carcinoma in situ retained expression of Dpc4. The frequent loss of Dpc4 expression in invasive MCNs indicates that genetic inactivation of Dpc4 occurs late in the neoplastic progression of these tumors and suggests a relationship to the development of invasion.

Dpc-4 protein is expressed in virtually all human intraductal papillary mucinous neoplasms of the pancreas: comparison with conventional ductal adenocarcinomas

DPC4 (MADH4, SMAD4) encodes a nuclear transcription factor shown to be genetically inactivated in over one-half of conventional infiltrating ductal adenocarcinomas of the pancreas. Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas have been suggested to be distinct neoplasms with a significantly less aggressive course than conventional ductal adenocarcinomas of the pancreas, but molecular comparisons of these tumor types have previously been impaired by technical difficulties. Recently, immunohistochemical labeling for the DPC4 gene product has been shown to be an extremely sensitive and specific marker for DPC4 gene alterations in pancreatic adenocarcinomas. Therefore, we analyzed the immunohistochemical expression of Dpc4 protein in 79 IPMNs using a previously characterized monoclonal antibody. Twenty-nine of the IPMNs also had an associated infiltrating adenocarcinoma available for analysis. The labeling patterns observed were compared to those we have previously reported for conventional ductal carcinomas. All 79 of the intraductal components of the IPMNs strongly expressed Dpc4 protein. In 77 of the 79 cases (97%), the labeling was diffusely positive, and in 2 of the 79 (3%) the labeling was focally positive. Dpc4 expression was seen in 28 (97%) of the associated 29 invasive cancers. The one infiltrating carcinoma that showed loss of Dpc4 expression was associated with an intraductal component which showed focal loss of Dpc4 expression. The strong and almost universal expression of Dpc4 in IPMNs contrasts sharply with the loss of Dpc4 expression seen in approximately 30% of in situ adenocarcinomas of the pancreas (so-called pancreatic intraepithelial neoplasms, grade 3; P: < 0.001) and in 55% of pancreatic duct carcinomas (P: < 0.0001). Differences in Dpc4 expression between IPMNs and ductal carcinomas suggest a fundamental genetic difference in tumorigenesis, which may relate to the significantly better clinical outcomes observed for IPMNs.

Distinct genetic profiles in colorectal tumors with or without the CpG island methylator phenotype

Colorectal cancers (CRCs) are characterized by multiple genetic (mutations) and epigenetic (CpG island methylation) alterations, but it is not known whether these evolve independently through stochastic processes. We have recently described a novel pathway termed CpG island methylator phenotype (CIMP) in CRC, which is characterized by the simultaneous methylation of multiple CpG islands, including several known genes, such as p16, hMLH1, and THBS1. We have now studied mutations in K-RAS, p53, DPC4, and TGFbetaRII in a panel of colorectal tumors with or without CIMP. We find that CIMP defines two groups of tumors with significantly different genetic lesions: frequent K-RAS mutations were found in CIMP(+) CRCs (28/41, 68%) compared with CIMP(-) cases (14/47, 30%, P = 0.0005). By contrast, p53 mutations were found in 24% (10/41) of CIMP(+) CRCs vs. 60% (30/46) of CIMP(-) cases (P = 0.002). Both of these differences were independent of microsatellite instability. These interactions between CIMP, K-RAS mutations, and p53 mutations were preserved in colorectal adenomas, suggesting that they occur early in carcinogenesis. The distinct combinations of epigenetic and genetic alterations in each group suggest that activation of oncogenes and inactivation of tumor suppressor genes is related to the underlying mechanism of generating molecular diversity in cancer, rather than simply accumulate stochastically during cancer development.

Smad4/DPC4 silencing and hyperactive Ras jointly disrupt transforming growth factor-beta antiproliferative responses in colon cancer cells

Smad4/DPC4 is a tumor suppressor gene frequently mutated or deleted in pancreatic and metastatic colon cancers. Smad4 acts as a cofactor that binds transforming growth factor-beta (TGF-beta) receptor-activated Smad2 and Smad3 generating transcriptional complexes. Using SW480.7 colon carcinoma cells, defective in Smad4 function, we have investigated whether this loss plays a role in the resistance of colon cancer cells to the antiproliferative effects of TGF-beta. SW480.7 cells contain only one Smad4 allele, which we found encodes a wild type protein that is not expressed. We generated SW480.7 cells conditionally expressing Smad4 via an ecdysone-inducible system. Smad4 expression in these cells failed to rescue TGF-beta antiproliferative and gene responses (c-myc down-regulation and induction of p21/Cip1 and plasminogen activator inhibitor-1). SW480.7 cells contain an activated Ki-ras oncogene. Hyperactivation of Ras can inhibit Smad nuclear accumulation by their phosphorylation at mitogen-activated protein kinase sites. Co-transfection into SW480.7 cells of Smad4 together with a Ras phosphorylation-resistant Smad3 (but not with wild type Smad2, Smad3, adenomatous polyposis coli (APC), or TGF-beta type II receptor) restored the TGF-beta antiproliferative response. These results suggest that loss of Smad4 function by both deletion and silencing and inhibition of Smad2/3 function by a hyperactive Ras pathway jointly prevent TGF-beta antiproliferative responses in SW480.7 colon cancer cells.

DPC4/SMAD4 gene alterations in human cancer, and their functional implications

The vast majority of pancreatic carcinomas have allelic loss of chromosome 18. Detailed analysis revealed a consensus region of homozygous deletion at 18q21.1 in one third of pancreatic carcinomas. The DPC4 gene (also known as SMAD4) was located in this region, and was found to be inactivated by intragenic mutations in another 20% of pancreatic carcinomas. The Dpc4 protein was shown to mediate TGF beta-stimulated gene transcription through sequence-specific binding to DNA. Eleven mutant Dpc4 proteins, identified in human carcinomas, were all found to be impaired in their ability to regulate gene transcription. A functional grouping of the mutant proteins could be made in those that were deficient in DNA binding, those that had impaired nuclear translocation, and those that had affected their transcription activation domain. The results imply gene transcription mediated by Dpc4 as a critical tumour suppressive pathway in pancreatic carcinoma.

Smad2 and Smad4 gene mutations in hepatocellular carcinoma

TGF-beta is a negative regulator of liver growth. Smad family of genes, as mediators of TGF-beta pathway, are candidate tumor suppressor genes in hepatocellular carcinoma (HCC). We studied 35 HCC and non-tumour liver tissues for possible mutations in Smad2 and Smad4 genes. Three tumours displayed somatic mutations; two in Smad4 (Asp332Gly and Cys401Arg) and one in Smad2 (Gln407Arg) genes. All three mutations were A:T --> G:C transitions suspected to result from oxidative stress as observed in mitochondrial DNA. These observation demonstrate that TGF-beta pathway is altered in hepatocellular carcinoma.

Immortalized pancreatic duct cells in vitro and in vivo

Although pancreatic adenocarcinoma has become one of the best characterized malignant diseases, severe diagnostic and therapeutic problems are still associated with this disease. The establishment of a molecular model of pancreatic carcinogenesis may provide tools that could result in earlier diagnosis of this disease and, in turn, improves prognosis. Since pancreatic adenocarcinoma seems to originate in epithelial cells in the pancreatic ducts, cultivation of native pancreatic duct epithelial cells (PDEC) is the initial step in the establishment of an in vitro model of pancreatic carcinogenesis. As these native cells survive only a short period in culture, the aim of this study was to establish a stable pancreatic duct cell line by immortalization with the SV40 large T antigen. Furthermore, initial steps in pancreatic carcinogenesis should possibly be imitated by additional transfections of mutated ki-ras and/or mutated p53 genes. By optimization of the isolation protocol and the culture medium, yield as well as proliferative activity of isolated PDEC was increased considerably. Transfection of SV40 large T antigen resulted in an increase in the proliferative lifetime of the isolated cells, but no real immortal phenotype was obtained. Moreover, one step in the transformation from the normal to the malignant phenotype was imitated successfully by additional transfection of mutated ki-ras.

Involvement of mutations in the DPC4 promoter in endometrial carcinoma development

To define the target of chromosome 18q loss of heterozygosity, which is prevalent in endometrial carcinomas, we made a deletion map from 64 tumors. Loss of heterozygosity on 18q was found in 20 tumors. Among these, 14 tumors carried deletions at the 18q21.1 region, where the DPC4 gene is located. DPC4 transcription was disturbed in all six of the tumors with deletions at 18q21.1 examined, which sharply contrasted with the positive transcription in 12 tumors that retained heterozygosity at the 18q21.1 region. However, in the 14 tumors with the 18q21.1 deletions, the remaining allele had the wild-type sequence of the DPC4 coding region instead of somatic mutations in the DPC4 coding region. We found a one- and two-base substitutions in the DPC4 promoter in two of the six tumors that showed disturbed DPC4 transcription. Chloramphenicol acetyltransferase assays clearly demonstrated that the mutant promoters had the potential to suppress or silence DPC4 transcription, implicating the DPC4 gene in endometrial carcinoma.

Mutations in DPC4 (SMAD4) cause juvenile polyposis syndrome, but only account for a minority of cases

Juvenile polyps are present in a number of Mendelian disorders, sometimes in association only with gastrointestinal cancer [juvenile polyposis syndrome (JPS)] and sometimes as part of known syndromes (Cowden, Gorlin and Banayan-Zonana) in association with developmental abnormalities, dysmorphic features or extra-intestinal tumours. Recently, a gene for JPS was mapped to 18q21.1 and the candidate gene DPC4 (SMAD4) was shown to carry frameshift mutations in some JPS families. We have analysed eight JPS families for linkage to DPC4. Overall, there was no evidence for linkage to DPC4; linkage could be excluded in two of the eight pedigrees and was unlikely in two others. We then tested these eight families and a further 13 familial and sporadic JPS cases for germline mutations in DPC4. Just one germline DPC4 mutation was found (in a familial JPS patient from a pedigree unsuitable for linkage analysis). Like all three previously reported germline mutations, this variant occurred towards the C-terminus of the DPC4 protein. However, our patient's mutation is a missense change (R361C); somatic missense mutations in DPC4 have been reported previously in tumours. We therefore confirm DPC4 as a cause of JPS, but show that there is considerable remaining, uncharacterized genetic heterogeneity in this disease.

Recent discoveries in cancer genetics of exocrine pancreatic neoplasia

Within the past 4 years major advances in our understanding of pancreatic carcinogenesis have been made. The discovery of a high frequency of mutations in the tumor suppressor genes p16 and p53 together with an extraordinary high rate of K-ras mutations have shed light on how the disturbance of cell cycle control is a major hallmark in this tumor type. Furthermore, another very recently identified tumor suppressor gene, DPC4 (deleted in pancreatic carcinoma, locus 4), revealed that the TGFbeta-Smad signalling pathway is also likely to contribute to the development of this tumor type. It is now hoped that our improved knowledge of the molecular profile of pancreatic carcinoma will also translate into better diagnostic and therapeutic options to deal with this dismal disease.

Mutations in the SMAD4/DPC4 gene in juvenile polyposis

Familial juvenile polyposis is an autosomal dominant disease characterized by a predisposition to hamartomatous polyps and gastrointestinal cancer. Here it is shown that a subset of juvenile polyposis families carry germ line mutations in the gene SMAD4 (also known as DPC4), located on chromosome 18q21.1, that encodes a critical cytoplasmic mediator in the transforming growth factor-beta signaling pathway. The mutant SMAD4 proteins are predicted to be truncated at the carboxyl-terminus and lack sequences required for normal function. These results confirm an important role for SMAD4 in the development of gastrointestinal tumors.