Elevated c-Src tyrosine kinase activity in premalignant epithelia of ulcerative colitis

Dendrobium huoshanense in the treatment of ulcerative colitis: Network pharmacology and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Dendrobium huoshanense C. Z. Tang et S. J. Cheng (DH) is a traditional medicinal herb with a long history of medicinal use. DH has been recorded as protecting the gastrointestinal function. Modern pharmacology research shows that DH regulates intestinal flora, intestinal mucosal immunity, gastrointestinal peristalsis and secretion of digestive juices. At the same time, some studies have shown that DH has a good therapeutic effect on ulcerative colitis, but its mechanism of action has not been fully elucidated.

AIMS OF THIS STUDY

To investigate the mechanism and effect of Dendrobium huoshanense C. Z. Tang et S. J. Cheng (DH) in the treatment of ulcerative colitis (UC) by combining network pharmacology and in vivo experimental validation.

METHODS

A network pharmacology approach was used to perform component screening, target prediction, PPI network interaction analysis, GO and KEGG enrichment analysis to initially predict the mechanism of DH treatment for UC. Then, the mechanism was validated with the UC mouse model induced by 3% DSS.

RESULTS

Based on the network pharmacological analysis, a comprehensive of 101 active components were identified, with 19 of them potentially serving as the crucial elements in DH's effectiveness against UC treatment. Additionally, the study revealed 314 potential core therapeutic targets along with the top 5 key targets: SRC, STAT3, AKT1, HSP90AA1, and PIK3CA. In experiments conducted on live mice with UC, DH was found to decrease the levels of IL-6 and TNF-α in the blood, while increasing the levels of IL-10 and TGF-β. This led to notable improvements in colon length, injury severity, and an up-regulation of SRC, STAT3, HSP90AA1, PIK3CA, p-AKT1 and PI3K/AKT signaling pathway expression in the colon tissue.

CONCLUSIONS

In this study, the active components and main targets of DH for UC treatment were initially forecasted, and the potential mechanism was investigated through network pharmacology. These findings offer an experimental foundation for the clinical utilization of DH.

Molecular Pathogenesis of Colitis-associated Colorectal Cancer: Immunity, Genetics, and Intestinal Microecology

Patients with inflammatory bowel disease (IBD) have a high risk for colorectal cancer (CRC). This cancer type, which is strongly associated with chronic inflammation, is called colitis-associated CRC (CAC). Understanding the molecular pathogenesis of CAC is crucial to identify biomarkers necessary for early diagnosis and more effective treatment directions. The accumulation of immune cells and inflammatory factors, which constitute a complex chronic inflammatory environment in the intestinal mucosa, may cause oxidative stress or DNA damage to the epithelial cells, leading to CAC development and progression. An important feature of CAC is genetic instability, which includes chromosome instability, microsatellite instability, hypermethylation, and changes in noncoding RNAs. Furthermore, the intestinal microbiota and metabolites have a great impact on IBD and CAC. By clarifying immune, genetic, intestinal microecology, and other related pathogenesis, CAC may be more predictable and treatable.

Exploring the Targets and Molecular Mechanisms of Thalidomide in the Treatment of Ulcerative Colitis: Network Pharmacology and Experimental Validation

BACKGROUND

Ulcerative colitis (UC) is a chronic, nonspecific, inflammatory disease of the intestine with an unknown cause. Thalidomide (THA) has been shown to be an effective drug for the treatment of UC. However, the molecular targets and mechanism of action of THA for the treatment of UC are not yet clear.

OBJECTIVES

Combining network pharmacology with in vitro experiments, this study aimed to investigate the potential targets and molecular mechanisms of THA for the treatment of UC.

METHODS

Firstly, relevant targets of THA against UC were obtained from public databases. Then, the top 10 hub targets and key molecular mechanisms of THA for UC were screened based on the network pharmacology approach and bioinformatics method. Finally, an in vitro cellular inflammation model was constructed using lipopolysaccharide (LPS) induced intestinal epithelial cells (NCM460) to validate the top 10 hub targets and key signaling pathways.

RESULTS

A total of 121 relevant targets of THA against UC were obtained, of which the top 10 hub targets were SRC, LCK, MAPK1, HSP90AA1, EGFR, HRAS, JAK2, RAC1, STAT1, and MAP2K1. The PI3K-Akt pathway was significantly associated with THA treatment of UC. In vitro experiments revealed that THA treatment reversed the expression of HSP90AA1, EGFR, STAT1, and JAK2 differential genes. THA was able to up- regulate the mRNA expression of pro-inflammatory factor IL-10 and decrease the mRNA levels of anti-inflammatory factors IL-6, IL-1β, and TNF-α. Furthermore, THA also exerted anti-inflammatory effects by inhibiting the activation of the PI3K/Akt pathway.

CONCLUSION

THA may play a therapeutic role in UC by inhibiting the PI3K-Akt pathway. HSP90AA1, EGFR, STAT1, and JAK2 may be the most relevant potential therapeutic targets for THA in the treatment of UC.

Immune-related biomarkers shared by inflammatory bowel disease and liver cancer

It has been indicated that there is an association between inflammatory bowel disease (IBD) and hepatocellular carcinoma (HCC). However, the molecular mechanism underlying the risk of developing HCC among patients with IBD is not well understood. The current study aimed to identify shared genes and potential pathways and regulators between IBD and HCC using a system biology approach. By performing the different gene expression analyses, we identified 871 common differentially expressed genes (DEGs) between IBD and HCC. Of these, 112 genes overlapped with immune genes were subjected to subsequent bioinformatics analyses. The results revealed four hub genes (CXCL2, MMP9, SPP1 and SRC) and several other key regulators including six transcription factors (FOXC1, FOXL1, GATA2, YY1, ZNF354C and TP53) and five microRNAs (miR-124-3p, miR-34a-5p, miR-1-3p, miR-7-5p and miR-99b-5p) for these disease networks. Protein-drug interaction analysis discovered the interaction of the hub genes with 46 SRC-related and 11 MMP9- related drugs that may have a therapeutic effect on IBD and HCC. In conclusion, this study sheds light on the potential connecting mechanisms of HCC and IBD.

An Update on Surveillance in Ulcerative Colitis

PURPOSE OF REVIEW

Patients with long-standing ulcerative colitis have an increased risk for the development of colorectal cancer (CRC). Colitis-related dysplasia appears to confer the greatest risk. Colonoscopic surveillance to detect dysplasia has been advocated by gastrointestinal societies. The aim of surveillance is the reduction of mortality and morbidity of CRC through detection and resection of dysplasia or detecting CRC at an earlier and potentially curable stage. Traditional surveillance has relied on mucosal assessment with targeted biopsy of visible lesions and random biopsy sampling on the premise that dysplasia was not visible at endoscopy. Advances in optical technology permitting increased detection of dysplasia and evidence that most dysplasia is visible has had practice-changing implications.

RECENT FINDINGS

Emerging evidence favours chromoendoscopy (CE) for dysplasia detection and is gaining wider acceptance through recent international (International Consensus Statement on Surveillance and Management of Dysplasia in Inflammatory Bowel Disease (SCENIC)) recommendations and endorsed by many gastrointestinal societies. Adoption of CE as the gold standard of surveillance has been met with by scepticism, from conflicting data, operational barriers and the need to understand the true impact of increasingly higher dysplasia detection on overall CRC mortality. Valid debate notwithstanding, implementation of a risk stratification protocol that includes CE is an effective approach allowing earlier detection of dysplasia and colorectal neoplasia, determination of surveillance intervals with appropriate allocation of resources and limiting morbidity from CRC and colonoscopy itself. Further prospective data should define the true and long-term impact of dysplasia detection with modern techniques.

Actin stress fiber organization promotes cell stiffening and proliferation of pre-invasive breast cancer cells

Studies of the role of actin in tumour progression have highlighted its key contribution in cell softening associated with cell invasion. Here, using a human breast cell line with conditional Src induction, we demonstrate that cells undergo a stiffening state prior to acquiring malignant features. This state is characterized by the transient accumulation of stress fibres and upregulation of Ena/VASP-like (EVL). EVL, in turn, organizes stress fibres leading to transient cell stiffening, ERK-dependent cell proliferation, as well as enhancement of Src activation and progression towards a fully transformed state. Accordingly, EVL accumulates predominantly in premalignant breast lesions and is required for Src-induced epithelial overgrowth in Drosophila. While cell softening allows for cancer cell invasion, our work reveals that stress fibre-mediated cell stiffening could drive tumour growth during premalignant stages. A careful consideration of the mechanical properties of tumour cells could therefore offer new avenues of exploration when designing cancer-targeting therapies.

When cells acquire a malignant phenotype they become less stiff and this helps migration and invasion favouring metastasis. Here the authors show that Src-driven cell transformation and transition to a less stiff state follows an event of membrane stiffening due to stress fibres accumulation.

Inhibition of c-Yes induces differentiation of HT-29 human colon cancer stem cells through midbody elongation

Recent research suggests that a small group of cells, named cancer stem cells (CSCs), is responsible for initiating tumor formation, recurrence, and metastasis. c-Yes, a proto-oncogene that is a subfamily of Src family kinase, is often activated in human colon cancer; this implicates c-Yes in the onset and progression of the disease. The objective of this study was to investigate the correlation between c-Yes and CSCs. We performed a sphere formation assay and reverse transcription-polymerase chain reaction for studying the differentiation of HT-29 human colon CSCs. To demonstrate the specific role of c-Yes in CSCs, we performed live cell microscopy and a cell cycle assay. These study shows, for the first time, that c-Yes is enriched in CD133⁺ CSCs, compared to their CD133^- counterparts, and that c-Yes depletion in CD133⁺ cells induces cell differentiation. Moreover, c-Yes depletion was found to elongate the midbody and increase the proliferation doubling time. This also suggested that the misregulation of microtubules during chromosomal separation causes aneuploidy. Our results suggest that c-Yes may play a crucial role in initiating, maintaining, and driving the tumorigenic property of colon cancer.

The tyrosine phosphatase PTPRO sensitizes colon cancer cells to anti-EGFR therapy through activation of SRC-mediated EGFR signaling

Inappropriate activation of epidermal growth factor receptor (EGFR) plays a causal role in many cancers including colon cancer. The activation of EGFR by phosphorylation is balanced by receptor kinase and protein tyrosine phosphatase activities. However, the mechanisms of negative EGFR regulation by tyrosine phosphatases remain largely unexplored. Our previous results indicate that protein tyrosine phosphatase receptor type O (PTPRO) is down-regulated in a subset of colorectal cancer (CRC) patients with a poor prognosis. Here we identified PTPRO as a phosphatase that negatively regulates SRC by directly dephosphorylating Y416 phosphorylation site. SRC activation triggered by PTPRO down-regulation induces phosphorylation of both EGFR at Y845 and the c-CBL ubiquitin ligase at Y731. Increased EGFR phosphorylation at Y845 promotes its receptor activity, whereas enhanced phosphorylation of c-CBL triggers its degradation promoting EGFR stability. Importantly, hyperactivation of SRC/EGFR signaling triggered by loss of PTPRO leads to high resistance of colon cancer to EGFR inhibitors. Our results not only highlight the PTPRO contribution in negative regulation of SRC/EGFR signaling but also suggest that tumors with low PTPRO expression may be therapeutically targetable by anti-SRC therapies.

Src plays a key role in ADAM28 expression in v-src-transformed epithelial cells and human carcinoma cells

ADAM28, a disintegrin and metalloproteinase 28, is overexpressed by carcinoma cells with direct correlations with carcinoma cell proliferation and progression in human lung and breast carcinomas. However, the molecular mechanisms of ADAM28 gene expression in carcinoma cells remain elusive. Herein, we investigated the expression of ADAM28 in Madin-Darby canine kidney epithelial cells transformed by oncogenes, including v-src, LMP1, ErbB2, Ha-Ras, and c-Fos, and found that v-src transformants selectively induce ADAM28. Implantation of the v-src transformants showed a progressively growing tumor, which was significantly suppressed by local injections of anti-ADAM28 antibody. ADAM28 expression in v-src transformants was partially inhibited by treatment with inhibitors to Src kinase, mitogen-activated protein kinase kinase (MEK), phosphatidylinositol 3-kinase (PI3K), or mammalian target of rapamycin, and abrogated by v-Src kinase inhibitor, radicicol, or a mixture of MEK and PI3K inhibitors. Human carcinoma cell lines of the lung, breast, ovary, kidney, and colon showed ADAM28 expression, which was correlated with phosphorylation of c-Src and suppressed by the inhibitors in a similar way to v-src transformants. IHC of the human tumor tissues demonstrated co-expression of ADAM28 and phosphorylated Src in neoplastic cells of the breast, lung, and colon carcinomas and some adenomas of the colon, but not in nonneoplastic colon mucosa. Our data provide, to the best of our knowledge, the first evidence that Src is an inducer of ADAM28 gene expression through the MEK/extracellular signal-regulated kinase and PI3K/mammalian target of rapamycin pathways.

Plasminogen activator inhibitor-1 is increased in colonic epithelial cells from patients with colitis-associated cancer

BACKGROUND

Patients with long-term ulcerative colitis are at risk for developing colorectal cancer.

METHODS

Archival formalin-fixed paraffin-embedded tissue from ulcerative colitis patients who underwent a colectomy for high-grade dysplasia or carcinoma was examined for changes in expression of plasminogen activator inhibitor-1 (PAI-1) as well as other mediators of inflammation-associated cancer. Epithelia from areas of colons that showed histologic evidence of carcinoma, high-grade dysplasia, and epithelia that were not dysplastic or malignant but did contain evidence of prior inflammation (quiescent colitis) was microdissected using laser capture microscopy. mRNA was extracted from the microdissected tissue and PCR array analysis was performed. To extend our findings, PAI-1 protein levels were determined using immunohistochemistry.

RESULTS

The mRNA expression of PAI-1 is increased 6-fold (p=0.02) when comparing the carcinoma group to the quiescent colitis group; increases were also observed in NFKB2, REL, SRC, and VEGFA. The protein levels of PAI-1 are increased by 50% (p<0.001) in high-grade dysplasia and by 60% (p<0.001) in carcinoma when compared to the quiescent colitis group.

CONCLUSIONS

The increase in PAI-1 in high-grade dysplasia and carcinoma suggests a functional role for PAI-1 in malignant transformation in colitis-associated cancer. PAI-1 could also prove a useful diagnostic marker to identify patients at risk for neoplasia and it may be a useful therapeutic target to treat colitis-associated cancer.

Phosphorylated c-Src is a novel predictor for recurrence in cervical squamous cell cancer patients

AIMS

The molecular mechanisms of the tumorigenesis and recurrence of cervical cancer are poorly understood. The objective of this study was to analyze the expression of phosphorylated c-Src (phospho-c-Src) and its clinical significance in human cervical cancer.

METHODS

The expression of phospho-c-Src was determined by immunohistochemistry in a total of 127 cervical specimens including 20 normal cervix tissues, 20 cases of carcinoma in situ of cervix (CIS), and 87 cases of cervical squamous cell carcinoma (CSCC).

RESULTS

The expression of phospho-Src in normal cervix, CIS, and CSCC increased gradually in ascending order (p=0.026). In addition, the expression of phospho-Src was correlated with overall (p=0.037) and recurrence (p=0.001) survival of cervical cancer. In multivariate Cox regression analysis, phospho-Src expression was an independent prognosis factor for recurrence-free survival (p=0.004).

CONCLUSION

Our present study suggests that Src signaling may play essential role in cervical cancer progression. Phospho-Src expression may be considered as a prognostic marker to predict recurrence in CSCC.

Somatic mutations in CCK2R alter receptor activity that promote oncogenic phenotypes

The roles of cholecystokinin 2 receptor (CCK2R) in numerous physiologic processes in the gastrointestinal tract and central nervous system are well documented. There has been some evidence that CCK2R alterations play a role in cancers, but the functional significance of these alterations for tumorigenesis is unknown. We have identified six mutations in CCK2R among a panel of 140 colorectal cancers and 44 gastric cancers. We show that these mutations increase receptor activity, activate multiple downstream signaling pathways, increase cell migration, and promote angiogenesis. Our findings suggest that somatic mutations in CCK2R may promote tumorigenesis through deregulated receptor activity and highlight the importance of evaluating CCK2R inhibitors to block both the normal and mutant forms of the receptor.

Src-signaling interference impairs the dissemination of blood-borne tumor cells

Although solid tumors continuously shed cells, only a small fraction of the neoplastic cells that enter the blood stream are capable of establishing metastases. In order to be successful, these cells must attach, extravasate, proliferate and induce angiogenesis. Preclinical studies have shown that small-molecule ATP-competitive Src kinase inhibitors can effectively impair metastasis-associated tumor cell functions in vitro. However, the impact of these agents on the metastatic cascade in vivo is less well understood. In the present studies, we have examined the ability of saracatinib, a dual-specific, orally available inhibitor of Src and Abl protein tyrosine kinases, to interfere with the establishment of lung metastases in mice by tumor cells introduced into the blood stream. The results demonstrate that Src inhibition most effectively interferes with the establishment of secondary tumor deposits when treatments are administered while tumor cells are in the initial phases of dissemination.

Genetic variability in EGFR, Src and HER2 and risk of colorectal adenoma and cancer

The EGFR signaling pathway is involved in carcinogenesis at multiple sites, particularly colorectal cancer, and is a target of colorectal cancer chemotherapy. EGFR signaling is linked to pro-carcinogenic mechanisms, including cell proliferation, survival, angiogenesis, and more recently prostaglandin synthesis. Genetic variability in this pathway has not yet been studied in relation to colorectal carcinogenesis. In three case-control studies of colorectal adenoma (n=485 cases/578 controls), colon cancer (n=1424 cases/1780 controls) and rectal cancer (n=583 cases/775 controls), we investigated associations between candidate SNPs, tagSNPs and haplotypes in EGFR signaling (EGFR, Src, and HER2) and risk. We also examined associations with tumor subtypes: TP53 and KRAS2 mutations, CpG island methylator phenotype, and microsatellite instability. All three studies were genotyped using an identical Illumina GoldenGate assay, allowing thorough investigation of genetic variability across stages and locations of colorectal neoplasia. The EGFR tagSNP 142572T>C (rs3752651) CC genotype was associated with a suggested increased risk for both colon (OR: 1.40; 95% CI: 1.00-1.96; p-trend=0.04) and rectal cancer (OR: 1.39; 95% CI: 0.81-2.41; p-trend=0.65). In tumor subtype analyses, the association was limited to TP53-mutated colon tumors. Using the Chatterjee 1 df Tukey test to assess gene-gene interactions, we observed a statistically significant (p<0.01) interaction between SNPs in EGFR and Src for colorectal adenoma risk. The association with EGFR 142572 should be investigated in additional studies and the significant gene-gene interaction between EGFR and Src in relation to adenoma risk suggests that these two genes are jointly affecting early stages in colorectal carcinogenesis and requires further follow-up.

Comparative role of acetylation along c-SRC/ETS1 signaling pathway in bone metastatic and invasive mammary cell phenotypes

Metastatic cells switch between different modes of migration through supramolecular plasticity mechanism(s) still largely unknown. The aim of the present paper was to clarify some molecular aspects of the epigenetic control of migration of 1833-bone metastatic cells compared to MDA-MB231-parental mammary carcinoma cells. Active c-Src overexpression enhanced 1833-cell spontaneous migration and CXCR4-mediated chemoinvasion toward CXCL12 ligand. Only in metastatic cells, in fact, c-Src seemed to stabilize nuclear CXCR4-protein receptor possibly due to tyrosine phosphorylation, by impairing protein-degradative smear and causing instead an electrophoretic-mobility shift; the cytosolic steady-state level of CXCR4 was enhanced, and the protein appeared also phosphorylated. These findings suggested the triggering of unique signaling pathways in metastasis for homing of breast-cancer cells to congenial environment of specific organs. Microenvironmental stimuli activating c-Src might influence Ets1 binding to CXCR4 promoter and consequent transactivation, as well as CXCR4 post-translational regulatory mechanisms such as phosphorylation. Enhancement of Ets1 activity and CXCR4 induction by c-Src overexpression were prevented by histone deacetylase (HDAC) blockade. In contrast, HDAC inhibition with trichostatin A increased cytosolic phosphorylated CXCR4 expression in MDA-MB231 cells, but Ets1 involvement was practically unneeded. c-Src might be suggested as a bio-marker predicting metastasis sensitivity patterns to HDAC inhibitors. Rationally designed and individualized therapy may become possible as more is learned about the target molecules of HDAC's inhibitory agents and their roles, as undertaken for CXCR4 that is likely to be crucial for homing, angiogenesis and survival in a c-Src-dependent manner in bone-metastatic mammary cells.

Inflammatory bowel disease-associated colorectal cancer: proctocolectomy and mucosectomy do not necessarily eliminate pouch-related cancer incidences

BACKGROUND

Colorectal cancer (CRC), the most lethal long-term complication of inflammatory bowel disease (IBD), is the culmination of a complex sequence of molecular and histologic derangements of the colon epithelium that are initiated and at least partially sustained by prolonged chronic inflammation. Dysplasia, the earliest histologic manifestation of this process, plays an important role in cancer prevention by providing the first clinical alert that this sequence is under way and by serving as an endpoint in colonoscopic surveillance of patients at high risk for CRC. Restorative proctocolectomy (RPC) is indicated for patients with IBD, specifically for ulcerative colitis that is refractory to medical treatment, emergency conditions, and/or in case of neoplastic transformation. Even after RPC with mucosectomy, pouch-related carcinomas have recently been reported with increasing frequency since the first report in 1984. We review IBD-associated CRC and pouch-related neoplasia prevalence, adverse events, risk factors, and surveillances.

METHODS

Literature of IBD-associated CRC patients and those undergoing RPC surgeries through 2010 were prospectively reviewed.

RESULTS

We found 12 studies from retrospective series and 15 case reports. To date, there are 43 reported cases of pouch-related cancers. Thirty-two patients had cancer in the anal transit zone (ATZ); of these, 28 patients had mucosectomy. Eleven patients had cancer found in the pouch body.

CONCLUSION

RPC with mucosectomy does not necessarily eliminate risks. There is little evidence to support routine surveillance of pouch mucosa and the ATZ except for patients associated with histological type C changes, sclerosing cholangitis, and unremitting pouchitis.

Molecular pathways underlying IBD-associated colorectal neoplasia: therapeutic implications

Chronic inflammatory diseases, depending upon the duration and severity, are frequently associated with an increased risk of developing cancer. A classic paradigm is the enhanced risk of colorectal cancer (CRC) in patients with inflammatory bowel disease (IBD). Carcinogenesis is a multifactorial process that involves accumulation of genetic defects, protein modification, and cell-matrix interaction. In this review, we discuss aspects of chronic inflammation in IBD that influence the development of CRC and highlight the key molecular mediators involved in this process. Also, we identify potential targets that could facilitate earlier detection of dysplasia. The targeted manipulation of specific molecules or pathways could provide opportunities for the development of therapeutic and chemopreventive interventions, which may prove effective in arresting the progression of colitis-associated cancer (CAC), with clinical implications.

EGFR(s) in aging and carcinogenesis of the gastrointestinal tract

Cells of the gastrointestinal (GI) mucosa are subject to a constant process of renewal which, in normal adults, reflects a balance between the rates of cell production and cell loss. Detailed knowledge of these events is, therefore, essential for a better understanding of the normal aging processes as well as many GI diseases, particularly malignancy, that represent disorders of tissue growth. In general, many GI dysfunctions, including malignancy, increase with advancing age, and aging itself is associated with alterations in structural and functional integrity of the GI tract. Although the regulatory mechanisms for age-related increase in the incidence of GI-cancers are yet to be fully delineated, recent evidence suggests a role for epidermal growth family receptors and its family members {referred to as EGFR(s)} in the development and progression of carcinogenesis during aging. The present communication discusses the involvement of EGFR(s) in regulating events of GI cancers during advancing age and summarizes the current available therapeutics targeting these receptors. The current review also describes the effectiveness of ErbB inhibitors as well as combination therapies. Additionally, the involvement of GI stem cells in the development of the age-related rise in GI cancers is emphasized.

Dasatinib sensitizes KRAS mutant colorectal tumors to cetuximab

KRAS mutation is a predictive biomarker for resistance to cetuximab (Erbitux®) in metastatic colorectal cancer (mCRC). This study sought to determine if KRAS mutant CRC lines could be sensitized to cetuximab using dasatinib (BMS-354825, sprycel®) a potent, orally bioavailable inhibitor of several tyrosine kinases, including the Src Family Kinases. We analyzed 16 CRC lines for: 1) KRAS mutation status, 2) dependence on mutant KRAS signaling, 3) expression level of EGFR and SFKs. From these analyses, we selected three KRAS mutant (LS180, LoVo, and HCT116) cell lines, and two KRAS wild type cell lines (SW48 and CaCo2). In vitro, using Poly-D-Lysine/laminin plates, KRAS mutant cell lines were resistant to cetuximab whereas parental controls showed sensitivity to cetuximab. Treatment with cetuximab and dasatinib showed a greater anti-proliferative effect on KRAS mutant line as compared to either agent alone both in vitro and in vivo. To investigate potential mechanisms for this anti-proliferative response in the combinatorial therapy we performed Human Phospho-kinase Antibody Array analysis measuring the relative phosphorylation levels of phosphorylation of 39 intracellular proteins in untreated, cetuximab, dasatinib or the combinatorial treatment in LS180, LoVo and HCT116 cells. The results of this experiment showed a decrease in a broad spectrum of kinases centered on the β-catenin pathway, the classical MAPK pathway, AKT/mTOR pathway and the family of STAT transcription factors when compared to the untreated control or monotherapy treatments. Next we analyzed tumor growth with cetuximab, dasatinib or the combination in vivo. KRAS mutant xenografts showed resistance to cetuximab therapy, whereas KRAS wild type demonstrated an anti-tumor response when treated with cetuximab. KRAS mutant tumors exhibited minimal response to dasatinib monotherapy. However, as in vitro, KRAS mutant lines exhibited a response to the combination of cetuximab and dasatinib. Combinatorial treatment of KRAS mutant xenografts resulted in decreased cell proliferation as measured by Ki67 and higher rates of apoptosis as measured by TUNEL. The data presented herein indicate that dasatinib can sensitize KRAS mutant CRC tumors to cetuximab and may do so by altering the activity of several key-signaling pathways. Further, these results suggest that signaling via the EGFR and SFKs may be necessary for cell proliferation and survival of KRAS mutant CRC tumors. This data strengthen the rationale for clinical trials in this genetic setting combining cetuximab and dasatinib.

Colorectal dysplasia in chronic inflammatory bowel disease: pathology, clinical implications, and pathogenesis

CONTEXT

Colorectal cancer, the most lethal long-term complication of chronic inflammatory bowel disease (IBD), is the culmination of a complex sequence of molecular and histologic derangements of the intestinal epithelium that are initiated and at least partially sustained by chronic inflammation. Dysplasia, the earliest histologic manifestation of this process, plays an important role in cancer prevention by providing the first clinical alert that this sequence is underway and serving as an endpoint in colonoscopic surveillance of patients at high risk for colorectal cancer.

OBJECTIVE

To review the histology, nomenclature, clinical implications, and molecular pathogenesis of dysplasia in IBD.

DATA SOURCE

Literature review and illustrations from case material.

CONCLUSIONS

The diagnosis and grading of dysplasia in endoscopic surveillance biopsies play a decisive role in the management of patients with IBD. Although interpathologist variation, endoscopic sampling problems, and incomplete information regarding the natural history of dysplastic lesions are important limiting factors, indirect evidence that surveillance may be an effective means of reducing cancer-related mortality in the population with IBD has helped validate the histologic criteria, nomenclature, and clinical recommendations that are the basis of current practice among pathologists and clinicians. Emerging technologic advances in endoscopy may permit more effective surveillance, but ultimately the greatest promise for cancer prevention in IBD lies in expanding our thus far limited understanding of the molecular pathogenetic relationships between neoplasia and chronic inflammation.

Ulcerative colitis and cancer

Patients with ulcerative colitis (UC) are at an increased risk for the development of colorectal cancer (CRC). Unlike sporadic CRC, the cancer in UC patients arises from a focal or multifocal dysplastic mucosa in areas of inflammation. The clinical features of UC-associated cancer are similar to those found in patients with hereditary non-polyposis colorectal cancer. As with other varieties of CRC, UC-associated cancer exhibits a variety of genetic and molecular changes/abnormalities. These abnormalities are however clustered in areas of mucosae with histological abnormalities. The magnitude and timing of these changes are however significantly different. Surveillance and identification of patients at risk for cancer are a challenging problem.

Downregulation of Rap1GAP in human tumor cells alters cell/matrix and cell/cell adhesion

Rap1GAP expression is decreased in human tumors. The significance of its downregulation is unknown. We show that Rap1GAP expression is decreased in primary colorectal carcinomas. To elucidate the advantages conferred on tumor cells by loss of Rap1GAP, Rap1GAP expression was silenced in human colon carcinoma cells. Suppressing Rap1GAP induced profound alterations in cell adhesion. Rap1GAP-depleted cells exhibited defects in cell/cell adhesion that included an aberrant distribution of adherens junction proteins. Depletion of Rap1GAP enhanced adhesion and spreading on collagen. Silencing of Rap expression normalized spreading and restored E-cadherin, beta-catenin, and p120-catenin to cell/cell contacts, indicating that unrestrained Rap activity underlies the alterations in cell adhesion. The defects in adherens junction protein distribution required integrin signaling as E-cadherin and p120-catenin were restored at cell/cell contacts when cells were plated on poly-l-lysine. Unexpectedly, Src activity was increased in Rap1GAP-depleted cells. Inhibition of Src impaired spreading and restored E-cadherin at cell/cell contacts. These findings provide the first evidence that Rap1GAP contributes to cell/cell adhesion and highlight a role for Rap1GAP in regulating cell/matrix and cell/cell adhesion. The frequent downregulation of Rap1GAP in epithelial tumors where alterations in cell/cell and cell/matrix adhesion are early steps in tumor dissemination supports a role for Rap1GAP depletion in tumor progression.

The role of Src in solid tumors

The proto-oncogene c-Src (Src) encodes a nonreceptor tyrosine kinase whose expression and activity are correlated with advanced malignancy and poor prognosis in a variety of human cancers. Nine additional enzymes with homology to Src have been identified and collectively are referred to as Src family kinases (SFKs). Together, SFKs represent the largest family of nonreceptor tyrosine kinases and interact directly with receptor tyrosine kinases, G-protein-coupled receptors, steroid receptors, signal transducers and activators of transcription, and molecules involved in cell adhesion and migration. These interactions lead to a diverse array of biological functions including proliferation, cell growth, differentiation, cell shape, motility, migration, angiogenesis, and survival. Studies investigating mutational activation of Src in human cancers suggest that this may be a rare event and that wild-type Src is weakly oncogenic. Thus, the role of Src in the development and progression of human cancer remains unclear. Recently, it was suggested that increased SFK protein levels and, more importantly, SFK tyrosine kinase activity are linked to cancer progression and metastatic disease by facilitating the action of other signaling proteins. This accumulating body of evidence indicates that SFKs may represent a promising therapeutic target for the treatment of solid tumors. This review discusses the role of SFKs in solid tumors and the recent therapeutic advances aimed at targeting this family of tyrosine kinases in cancer.

SRC promotes survival and invasion of lung cancers with epidermal growth factor receptor abnormalities and is a potential candidate for molecular-targeted therapy

Molecular-targeted therapy using tyrosine kinase inhibitors against epidermal growth factor receptor (EGFR) is an effective therapy for non-small cell lung cancer that harbor EGFR mutations. This study aimed to investigate the role of Src, a close EGFR associator, as a drug target in NSCLC cells with different EGFR genomic statuses. Src inhibition was achieved using 4-(4'-Phenoxyanilino)-6,7-dimethoxyquinazolinee (SKI-1) and the specificity of action was verified by RNA interference. The results showed that SKI-1 induced significant apoptosis in a dose-dependent manner in cancer cells with high basal Src activation. Activation of FAK and p130Cas was involved in Src-mediated invasion in SKI-1-sensitive cells. SKI-1 inhibited phosphorylation of EGFR as well as EGFR downstream effectors, such as signal transducers and activators of transcription 3/5, extracellular signal-regulated kinase 1/2 and AKT in the mutant cells but not the wild-type cells. This inhibition profile of EGFR implicates that induction of apoptosis and sensitivity of mutant cells to SKI treatment is mediated by EGFR and EGFR downstream pathways. Cotreatment with SKI-1 and gefitinib enhanced apoptosis in cancer cells that contained EGFR mutation and/or amplification. SKI-1 treatment alone induced significant apoptosis in H1975 cells known to be resistant to gefitinib. Src phosphorylation was shown by immunohistochemistry in around 30% of primary lung carcinomas. In 152 adenocarcinomas studied, p-Src was associated with EGFR mutations (P = 0.029). Overall, the findings indicated that Src could be a useful target for treatment of non-small cell lung cancer. Besides EGFR genomic mutations, other forms of EGFR and related family member abnormalities such as EGFR amplification might enhance SKI sensitivity.

Carcinogenesis in IBD: potential targets for the prevention of colorectal cancer

In patients with IBD, chronic colonic inflammation increases the risk of colorectal cancer, perhaps because inflammation predisposes these tissues to genomic instability. Carcinogenesis in the inflamed colon seems to follow a different sequence of genetic alterations than that observed in sporadic cancers in the uninflamed colon. In this Review, we focus on the genetic alterations in colitis-associated colorectal cancer that contribute to the acquisition of the essential hallmarks of cancer, and on how those alterations differ from sporadic colorectal cancers. Our intent is to provide a conceptual basis for categorizing carcinogenetic molecular abnormalities in IBD, and for understanding how cancer-preventive therapies might target reversal of acquired abnormalities in specific biochemical pathways.

Targeting Src signaling in metastatic bone disease

Src is a tyrosine kinase involved in the regulation of a range of cellular processes including proliferation, adhesion, motility and survival. In addition, it is a key regulator of bone metabolism. Src has been implicated in the pathogenesis of a number of cancers, and has been found to be overexpressed in breast, prostate, colorectal, pancreatic and nonsmall-cell lung tumors. There is also evidence that aberrant Src signaling may contribute to the increased osteoclastic activity associated with bone metastases. Bone metastases frequently occur in cancer patients with advanced disease. The metastasized cells disrupt normal bone remodeling pathways resulting in the release of growth factors that further promote tumor growth. Thus, a cycle of metastatic bone destruction is initiated, leading to compromised skeletal integrity and substantially reduced quality of life. Because of the role of Src in both cancer development and in bone metabolism, it may provide a therapeutic target for patients with bone metastases.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers. Although the precise cellular function remains to be elucidated, the current data implicate PTPIP51 in signaling cascades mediating proliferation, differentiation, apoptosis, and motility.

A novel Src kinase inhibitor reduces tumour formation in a skin carcinogenesis model

The Src family tyrosine kinases are key modulators of cancer cell invasion and metastasis and a number of Src kinase inhibitors are currently in clinical development for the treatment of solid tumours. However, there is growing evidence that Src is also upregulated at very early stages of epithelial cancer development. We have investigated the role of Src in mouse skin, which is one of the most tractable models of epithelial homoeostasis and tumorigenesis. We found that Src protein expression and activity was regulated during the normal hair cycle and was increased specifically during the proliferative anagen phase and also in response to the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). AZD0530, a selective Src inhibitor, prevented the TPA-induced proliferation of basal keratinocytes both in vivo and in vitro. Moreover, treatment with AZD0530 reduced papilloma formation following the well-established 7,12-dimethylbenz(a)anthracene/TPA skin carcinogenesis protocol but did not inhibit the subsequent proliferation of the papillomas. Furthermore, AZD0530 did not alter the malignant conversion of papillomas to squamous cell carcinoma suggesting a role for Src in early tumour development in the skin carcinogenesis model, rather than at later stages of tumour progression. Src expression and activity were also seen in human actinic keratoses that are hyperproliferative pre-malignant skin lesions, indicating that Src may also play a role in the early stages of human skin tumour development. Thus, Src inhibitors such as AZD0530 may therefore have chemopreventative properties in patients with hyperproliferative epidermal disorders.

Src family kinases mediate betel quid-induced oral cancer cell motility and could be a biomarker for early invasion in oral squamous cell carcinoma

Betel quid (BQ)-chewing oral cancer is a prevalent disease in many countries of Southeast Asia. Yet, the precise disease mechanism remains largely unknown. Here, we show that BQ extract-induced cell motility in three oral cancer cells (Ca9-22, SAS, and SCC9) presumably involves the Src family kinases (SFKs). Besides, BQ extract can markedly induce cell migration of wild type mouse embryonic fibroblasts (MEFs) but not MEFs lacking three SFK members, namely, Src, Yes, and Fyn, indicating the requirement of SFKs for BQ-induced cell motility. Betel quid extract can also elevate cellular SFK activities because phosphorylation of tyrosine 416 at the catalytic domain is increased, which in turn promotes phosphorylation of an in vitro substrate, enolase. Furthermore, we identified that areca nut, a major component of BQ, is the key factor accounting for BQ-induced cell migration and invasion through SFKs-mediated signaling pathways. Immunohistochemistry revealed that, particularly in BQ-chewing cases, the activity of SFKs was significantly higher in tumor-adjacent mucosa than that in solid tumor areas (P < .01). These results suggest a possible role of SFKs in tumor-host interface and thus in early tumor invasion in vivo. Consistent with this is the observation that activation of SFKs is colocalized with invasive tumor fronts in oral squamous cell carcinoma. Together, we conclude that SFKs may represent a potential biomarker of invasion and therapeutic target in BQ-induced oral cancer.

Src activity alters alpha3 integrin expression in colon tumor cells

Src kinase has been linked to increased motility in the progression and metastasis of human colon cancer, although the mechanisms are not fully understood. Integrins are involved in metastasis by mediating attachment and migration of cells, as well as through transducing signals. This study examines the link between Src and integrin activity in the metastatic process in colon cancer cells. To determine Src involvement in integrin expression, the human colon cancer cell line, HCT116, was transfected with an activated Src construct and assayed for its ability to attach to and migrate across collagen and laminin. These cells attached more readily and migrated less rapidly on the extracellular matrix (ECM) than did cells transfected with empty vector. Examination of integrin levels showed a decrease in the alpha3 subunit in Src transfected cells as well as decreased cell surface localization of alpha3 integrin. The downregulation of alpha3 integrin was reversed by inhibition of Src and by inhibition of MAP kinase. Inhibition of alpha3 integrin using shRNA resulted in decreased MMP7 secretion, a possible cause of decreased invasion with low alpha3 integrin expression. This study shows that Src overexpression downregulates alpha3 integrin total protein expression and localization to the cell surface of HCT116 colon cancer cells. This indicates that Src activity may enhance metastasis by altering alpha3 integrin expression.

Antiproliferative effect of sulindac in colonic neoplasia prevention: role of COOH-terminal Src kinase

Although the nonsteroidal anti-inflammatory drugs (NSAID) protection against colorectal cancer is well established, the molecular mechanisms remain unclear. We show herein that induction of the tumor suppressor gene COOH-terminal Src kinase (Csk) by NSAID is important for their antiproliferative and hence chemopreventive effects. In the azoxymethane-treated rat model of experimental colon carcinogenesis, sulindac treatment markedly induced Csk with a corresponding increase in inhibitory phosphorylation of Src (Tyr(527)). Sulindac-mediated Csk induction was replicated in the human colorectal cancer cell line HT-29, with a corresponding suppression of both Src kinase activity (63% of vehicle; P < 0.05) and E-cadherin tyrosine phosphorylation (an in vivo Src target). To determine the importance of Csk in NSAID antiproliferative activity, we stably transfected a Csk-specific short hairpin RNA (shRNA) vector into HT-29 cells, thereby blunting the sulindac-mediated Csk induction. These transfectants were significantly less responsive to the antiproliferative effect of sulindac sulfide (suppression of proliferating cell nuclear antigen was 21 +/- 2.3% in transfectants versus 45 +/- 4.23% in wild-type cells), with a corresponding mitigation of the sulindac-mediated G(1)-S-phase arrest (S-phase cells 48 +/- 3.6% versus 14 +/- 2.8% of vehicle respectively). Importantly, the Csk shRNA cells had a marked decrease in the cyclin-dependent kinase inhibitor p21(cip/waf1), a critical regulator of G(1)-S-phase progression (49% of wild-type cells). Moreover, although sulindac-mediated induction of p21(cip/waf1) was 113% in wild-type HT-29, this induction was alleviated in the Csk shRNA transfectants (65% induction; P < 0.01). Thus, this is the first demonstration that the antiproliferative activity of NSAID is modulated, at least partly, through the Csk/Src axis.

Myricetin suppresses UVB-induced skin cancer by targeting Fyn

Skin cancer is currently the most common type of human cancer in Americans. Myricetin, a naturally occurring phytochemical, has potent anticancer-promoting activity and contributes to the chemopreventive potential of several foods, including red wine. Here, we show that myricetin suppresses UVB-induced cyclooxygenase-2 (COX-2) expression in mouse skin epidermal JB6 P+ cells. The activation of activator protein-1 and nuclear factor-kappaB induced by UVB was dose-dependently inhibited by myricetin treatment. Western blot and kinase assay data revealed that myricetin inhibited Fyn kinase activity and subsequently attenuated UVB-induced phosphorylation of mitogen-activated protein kinases. Pull-down assays revealed that myricetin competitively bound with ATP to suppress Fyn kinase activity. Importantly, myricetin exerted similar inhibitory effects compared with 4-amino-5-(4-chloro-phenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, a well-known pharmacologic inhibitor of Fyn. In vivo mouse skin data also revealed that myricetin inhibited Fyn kinase activity directly and subsequently attenuated UVB-induced COX-2 expression. Mouse skin tumorigenesis data clearly showed that pretreatment with myricetin significantly suppressed UVB-induced skin tumor incidence in a dose-dependent manner. Docking data suggest that myricetin is easily docked to the ATP-binding site of Fyn, which is located between the N and C lobes of the kinase domain. Overall, these results indicated that myricetin exerts potent chemopreventive activity mainly by targeting Fyn in skin carcinogenesis.

Potential molecular mechanism for c-Src kinase-mediated regulation of intestinal cell migration

The ubiquitously expressed Src tyrosine kinases (c-Src, c-Yes, and c-Fyn) regulate intestinal cell growth and differentiation. Src activity is also elevated in the majority of malignant and premalignant tumors of the colon. The development of fibroblasts with the three ubiquitously expressed kinases deleted (SYF cells) has identified the role of Src proteins in the regulation of actin dynamics associated with increased cell migration and invasion. Despite this, unexpectedly nothing is known about the role of the individual Src kinases on intestinal cell cytoskeleton and/or cell migration. We have previously reported that villin, an epithelial cell-specific actin-modifying protein that regulates actin reorganization, cell morphology, cell migration, cell invasion, and apoptosis, is tyrosine-phosphorylated. In this report using the SYF cells reconstituted individually with c-Src, c-Yes, c-Fyn, and wild type or phosphorylation site mutants of villin, we demonstrate for the first time the absolute requirement for c-Src in villin-induced regulation of cell migration. The other major finding of our study is that contrary to previous reports, the nonreceptor tyrosine kinase, Jak3 (Janus kinase 3), does not regulate phosphorylation of villin or villin-induced cell migration and is, in fact, not expressed in intestinal epithelial cells. Further, we identify SHP-2 and PTP-PEST (protein-tyrosine phosphatase proline-, glutamate-, serine-, and threonine-rich sequence) as negative regulators of c-Src kinase and demonstrate a new function for these phosphatases in intestinal cell migration. Together, these data suggest that in colorectal carcinogenesis, elevation of c-Src or down-regulation of SHP-2 and/or PTP-PEST may promote cancer metastases and invasion by regulating villin-induced cell migration and cell invasion.

Chemoresistant KM12C colon cancer cells are addicted to low cyclic AMP levels in a phosphodiesterase 4-regulated compartment via effects on phosphoinositide 3-kinase

One of the major problems in treating colon cancer is chemoresistance to cytotoxic chemotherapeutic agents. There is therefore a need to devise new strategies to inhibit colon cancer cell growth and survival. Here, we show that a combination of low doses of the adenylyl cyclase activator forskolin together with the specific cyclic AMP (cAMP) phosphodiesterase-4 (PDE4) inhibitor rolipram, but not the cAMP phosphodiesterase-3 (PDE3) inhibitor cilostamide, causes profound growth arrest of chemoresistant KM12C colon cancer cells. Low-dose forskolin causes KM12C cells to exit the cell cycle in G1 by inducing p27(Kip1) and primes cells for apoptosis on addition of rolipram. The effect of the low-dose forskolin/rolipram combination is mediated by displacement of the phosphatidylinositol 3,4,5-trisphosphate/phosphoinositide 3-kinase signaling module from the plasma membrane and suppression of the Akt/protein kinase-B oncogene pathway, to which KM12C cells are addicted for growth. The cAMP and phosphoinositide 3-kinase pathways form a critical intersection in this response, and reexpression of the tumor suppressor lipid phosphatase, phosphatase and tensin homologue, which is commonly lost or mutated in colon cancer, sensitizes KM12C cells to growth inhibition by challenge with low-dose forskolin. Certain chemoresistant colon cancer cells are therefore exquisitely sensitive to subtle elevation of cAMP by a synergistic low-dose adenylyl cyclase activator/PDE4 inhibitor combination. Indeed, these cells are addicted to maintenance of low cAMP concentrations in a compartment that is regulated by PDE4. Well-tolerated doses of PDE4 inhibitors that are already in clinical development for other therapeutic indications may provide an exciting new strategy for the treatment of colon cancer.

Molecular biology of dysplasia and cancer in inflammatory bowel disease

Colorectal cancer (CRC) develops from a dysplastic precursor lesion, regardless of whether it arises sporadically, in the setting of high-risk hereditary conditions, or in the context of chronic inflammation like inflammatory bowel disease (IBD). This review focuses on the molecular alterations associated with CRC pathogenesis in IBD. Although none of the molecular alterations to be discussed have yet been integrated into clinical practice, there is potential for molecular diagnostics to enhance the management of patients with long-standing IBD.

Src kinase phosphorylates vascular endothelial-cadherin in response to vascular endothelial growth factor: identification of tyrosine 685 as the unique target site

Src-family tyrosine kinases are regulatory proteins that play a pivotal role in the disorganization of cadherin-dependent cell-cell contacts. We previously showed that Src was associated with vascular endothelial (VE)-cadherin and that tyrosine phosphorylation level of VE-cadherin was dramatically increased in angiogenic tissues as compared to quiescent tissues. Here, we examined whether VE-cadherin was a direct substrate for Src in vascular endothelial growth factor (VEGF)-induced VE-cadherin phosphorylation, and we identified the target tyrosine sites. Co-transfections of Chinese hamster ovary cells (CHO) cells with VE-cadherin and constitutively active Src (Y530F) resulted in a robust tyrosine phosphorylation of VE-cadherin that was not detected with kinase-dead Src (K298M). In an in vitro Src assay, the VE-cadherin cytoplasmic domain is directly phosphorylated by purified Src as well as the tyrosine residue 685 (Tyr)685-containing peptide RPSLY(685)AQVQ. VE-cadherin peptide mapping from human umbilical vein endothelial cells stimulated by VEGF and VE-cadherin-CHO cells transfected with active Src revealed that Y685 was the unique phosphorylated site. The presence of PhosphoY685 was confirmed by its ability to bind to C-terminal Src kinase-SH2 domain in a pull-down assay. Finally, we found that in a VEGF-induced wound-healing assay, cadherin adhesive activity was impaired by Src kinase inhibitors. These data identify that VEGF-induced-VE-cadherin tyrosine phosphorylation is mediated by Src on Y685, a process that appears to be critical for VEGF-induced endothelial cell migration.

Constitutively active CCK2 receptor splice variant increases Src-dependent HIF-1 alpha expression and tumor growth

Gastrointestinal (GI) cancers ectopically express multiple splice variants of the cholecystokinin-2 (CCK(2))/gastrin receptor; however, their relative contributions to the cancer phenotype are unknown. The aim of this study was to compare the effects of CCK(2) receptor (CCK(2)R) and CCK(2i4sv)R expression on cell growth both in vitro and in vivo using a human epithelial cell model, HEK239. In vitro, receptor variant expression did not affect cell proliferation either in the absence or presence of agonist. However, in vivo, the expression of CCK(2i4sv)R, but not CCK(2)R, increases HEK293 tumor growth in a constitutive, Src-dependent manner. Enhanced tumorigenicity of CCK(2i4sv)R is associated with an Src-dependent increase in the transcription factor, hypoxia-inducible factor-1alpha, its downstream target, vascular endothelial growth factor and tumor micro-vessel density, suggesting that CCK(2i4sv)R may contribute to the growth and spread of GI cancers through agonist-independent mechanisms that enhance tumor angiogenesis.

Dok-1 independently attenuates Ras/mitogen-activated protein kinase and Src/c-myc pathways to inhibit platelet-derived growth factor-induced mitogenesis

The Dok adaptor proteins play key regulatory roles in receptor and non-receptor kinase-initiated signaling pathways. Dok-1, the prototype member of this family, negatively regulates cell proliferation elicited by numerous growth factors, including platelet-derived growth factor (PDGF). However, how Dok-1 exerts its negative effect on mitogenesis has remained elusive. Using Dok-1 knockout cells and Dok-1 mutants deficient in binding to specific Dok-1-interacting proteins, we show that Dok-1 interferes with PDGF-stimulated c-myc induction and Ras/mitogen-activated protein kinase (MAPK) activation by tethering different signaling components to the cell membrane. Specifically, Dok-1 attenuates PDGF-elicited c-myc induction by recruiting Csk to active Src kinases, whereupon their activities and consequent c-myc induction are diminished. On the other hand, Dok-1 negatively regulates PDGF-induced MAPK activation by acting on Ras-GAP and at least one other Dok-1-interacting protein. Importantly, we demonstrate that Dok-1's actions on both of these signaling pathways contribute to its inhibitory effect on mitogenesis. Our data suggest a mechanistic basis for the inhibitory effect of Dok-1 on growth factor-induced mitogenesis and its role as a tumor suppressor.

SKI-606 decreases growth and motility of colorectal cancer cells by preventing pp60(c-Src)-dependent tyrosine phosphorylation of beta-catenin and its nuclear signaling

Inhibition of deregulated protein tyrosine kinases represents an attractive strategy for controlling cancer growth. However, target specificity is an essential aim of this strategy. In this report, pp60(c-Src) kinase and beta-catenin were found physically associated and constitutively activated on tyrosine residues in human colorectal cancer cells. The use of specific small-interfering RNAs (siRNA) validated pp60(c-Src) as the major kinase responsible for beta-catenin tyrosine phosphorylation in colorectal cancer. Src-dependent activation of beta-catenin was prevented by SKI-606, a novel Src family kinase inhibitor, which also abrogated beta-catenin nuclear function by impairing its binding to the TCF4 transcription factor and its trans-activating ability in colorectal cancer cells. These effects were seemingly specific, as cyclin D1, a crucial beta-catenin/TCF4 target gene, was also down-regulated by SKI-606 in a dose-dependent manner accounting, at least in part, for the reduced growth (IC50, 1.5-2.4 micromol/L) and clonogenic potential of colorectal cancer cells. Protein levels of beta-catenin remained substantially unchanged by SKI-606, which promoted instead a cytosolic/membranous retention of beta-catenin as judged by immunoblotting analysis of cytosolic/nuclear extracts and cell immunofluorescence staining. The SKI-606-mediated relocalization of beta-catenin increased its binding affinity to E-cadherin and adhesion of colorectal cancer cells, with ensuing reduced motility in a wound healing assay. Interestingly, the siRNA-driven knockdown of beta-catenin removed the effect of SKI-606 on cell-to-cell adhesion, which was associated with prolonged stability of E-cadherin protein in a pulse-chase experiment. Thus, our results show that SKI-606 operates a switch between the transcriptional and adhesive function of beta-catenin by inhibiting its pp60(c-Src)-dependent tyrosine phosphorylation; this could constitute a new therapeutic target in colorectal cancer.

Molecular mechanisms of hepatic metastasis in colorectal cancer

BACKGROUND

Colorectal cancer currently accounts for 11% of all cancers in the United States and is the second leading cause of cancer-related death, with the majority of deaths attributable to hepatic metastases. Many new studies are elucidating the complex molecular factors involved in this event, which could be used to generate clinically applicable screening and therapeutic tools.

METHODS

An initial Pubmed and Medline literature search using keywords such as, molecular factor, colorectal cancer, hepatic metastasis/es, and main headings, such as angiogenesis, was reviewed. Since there are many molecular factors involved in this process not all could be included in this review. The list of discussed gene products was limited to the most studied factors, identified by the number of references in the literature search, and additional recently discovered gene products with in-vivo evidence of strong metastasis association.

RESULTS

Twenty molecular factors were identified and included in the discussion of this review article. The molecular factors were separated into four groups based on their function, they are: proteolysis, adhesion, angiogenesis, and cell survival. All factors have a promising role as a screening or therapeutic target.

CONCLUSION

This review has identified the many recent advances in elucidating the pathways involved in colorectal cancer hepatic metastasis. By better understanding the many complex molecular events involved in metastasis, novel screening and therapeutic tools may be developed with the ultimate goal of preventing metastasis and increasing patient survival.

SRC gene expression in human cancer: the role of transcriptional activation

Human pp60c-Src (or c-Src) is a 60 kDa nonreceptor tyrosine kinase encoded by the SRC gene and is the cellular homologue to the potent transforming v-Src viral oncogene. c-Src functions at the hub of a vast array of signal transduction cascades that influence cellular proliferation, differentiation, motility, and survival. c-Src activation has been documented in upwards of 50% of tumors derived from the colon, liver, lung, breast, and pancreas. Therefore, a major focus has been to understand the mechanisms of c-Src activation in human cancer. Early studies concentrated on post-translational mechanisms that lead to increased c-Src kinase activity, which often correlated with overexpression of c-Src protein. More recently, the discovery of an activating SRC mutation in a small subset of advanced colon tumors has been reported. In addition, elevated SRC transcription has been identified as yet another mechanism contributing significantly to c-Src activation in a subset of human colon cancer cell lines. Interestingly, histone deacetylase (HDAC) inhibitors, agents with well-documented anti-cancer activity, repress SRC transcription in a wide variety of human cancer cell lines. Analysis of the mechanisms behind HDAC inhibitor mediated repression could be utilized in the future to specifically inhibit SRC gene expression in human cancer.

Altered regulation of Src upon cell detachment protects human lung adenocarcinoma cells from anoikis

Src plays an important role in cell proliferation, differentiation, adhesion, and migration. Altered Src activity has been strongly implicated in the development, growth, progression, and metastasis of human cancers. We have analysed the change and regulation of Src upon cell detachment in anoikis-resistant human lung adenocarcinoma cells and compared with that of relatively normal and anoikis-sensitive epithelial cells. We found that Src activity was increased in the anoikis-resistant lung tumor cells when they were detached and cultured in suspension. The detachment-induced Src activation in the tumor cells compensates for the loss of cell survival signals caused by disruption of cell--matrix interactions and contributes to anoikis resistance of the tumor cells. Pyk2, rather than PI 3K/Akt or Erk, appears to be the key downstream effecter of Src in mediating the cell survival signals. The increased Src activity is mainly due to the phosphorylation of Tyr-419, rather than the dephosphorylation of Tyr-530 of Src protein. PDGFR, not FAK or EGFR, appears to be the upstream protein tyrosine kinase responsible for the detachment-induced Src activation in the lung tumor cells. The increased Src activity upon cell detachment may contribute to the metastasis potential of malignant tumors.

SRC-mediated phosphorylation of focal adhesion kinase couples actin and adhesion dynamics to survival signaling

Integrin-associated focal adhesions not only provide adhesive links between cellular actin and extracellular matrix but also are sites of signal transmission into the cell interior. Many cell responses signal through focal adhesion kinase (FAK), often by integrin-induced autophosphorylation of FAK or phosphorylation by Src family kinases. Here, we used an interfering FAK mutant (4-9F-FAK) to show that Src-dependent FAK phosphorylation is required for focal adhesion turnover and cell migration, by controlling assembly of a calpain 2/FAK/Src/p42ERK complex, calpain activation, and proteolysis of FAK. Expression of 4-9F-FAK in FAK-deficient fibroblasts also disrupts F-actin assembly associated with normal adhesion and spreading. In addition, we found that FAK's ability to regulate both assembly and disassembly of the actin and adhesion networks may be linked to regulation of the protease calpain. Surprisingly, we also found that the same interfering 4-9F-FAK mutant protein causes apoptosis of serum-deprived, transformed cells and suppresses anchorage-independent growth. These data show that Src-mediated phosphorylation of FAK acts as a pivotal regulator of both actin and adhesion dynamics and survival signaling, which, in turn, control apparently distinct processes such as cell migration and anchorage-independent growth. This also highlights that dynamic regulation of actin and adhesions (which include the integrin matrix receptors) is critical to signaling output and biological responses.