Indeed, unlike in T ALL, genetic alter ations in Notch genes have not been identified Crenolanib CP-868596 in solid tumors. However, Notch signaling appears to be cru cial in many solid tumors, including cancers of the breast, colon, pancreas, prostate and central nervous system. Interestingly, Notch signaling also seems to play a contradictory tumor suppressor role in mouse keratinocytes, pancreatic and hepatocellular carcin oma, and small cell lung cancer. Taken together, these observations indicate that Notch exerts its effects in solid tumors as a result of aberrant activation of the pathway. Moreover, the cellular interpretation and out come of aberrant Notch activity is highly dependent on contextual cues, such as interactions with the tumor microenvironment and crosstalk with other signaling pathways.

Intrahepatic cholangiocarcinoma is the second most prevalent intrahepatic primary cancer and has poor prognosis. The lethality of the disease is caused by both rapid tumor growth and the tendency to invade adjacent organs and metastasize. Mounting evidence has demonstrated that EMT is as sociated with the invasive and migratory ability of cancer cells, conferring enhanced metastatic properties to these cells. Increased expression of Notch1 has been shown to promote EMT in glioma, however, the role of Notch1 in ICC remains unclear. In the present study, we found that Notch1 mRNA and ICN expression is higher in ICC tissue than in noncancerous tissue adja cent to the cancer lesions, and all cancer cell lines expressed high levels of ICN compared with normal bil iary epithelial cells.

Taken together, aberrant Notch1 ex pression in both ICC tissues and ICC cells suggests that increased Notch1 expression might be associated with tumor progression. To elucidate the effects of Notch1 expression in ICC cells, separate over expression and knockdown experi ments were conducted in ICC 9810 cells. Notch1 cDNA was introduced into ICC 9810 cells, and Notch1 protein expression was successfully induced. Notch1 over expres sion promoted migration and Rac1 activation in these cells. In contrast, the down regulation of Notch1 inhibited the migration of ICC 9810 cells and resulted in dramatic decreases in Rac1 activity compared to control cells. Sub stantial evidence has indicated that increased Notch1 expression is accompanied by enhanced expression of SMA and Vimentin and loss of E cadherin expres sion, which are hallmarks of EMT.

The Rho like GTPase Rac1 is involved in migration and adhesion by modulating the actin cytoskeleton. Rac1 acts as a molecular switch, cycling between an ac tive GTP bound state and an inactive GDP bound state, which is controlled by GEF. Rac1 is preferentially activated at the leading edge of migrating cells where it induces the formation sellekchem of actin rich lamellipodia pro trusions that are thought to be a key driving force for membrane extension and cell movement.