C3G forms complexes with Bcr-Abl and p38α MAPK at the focal adhesions in chronic myeloid leukemia cells: implication in the regulation of leukemic cell adhesion

Background: Previous studies by our group and others have shown that C3G interacts with Bcr-Abl through its SH3-b domain. Results: In this work we show that C3G and Bcr-Abl form complexes with the focal adhesion (FA) proteins CrkL, p130Cas, Cbl and Abi1 through SH3/SH3-b interactions. The association between C3G and Bcr-Abl decreased upon Abi1 or p130Cas knock-down in K562 cells, which suggests that Abi1 and p130Cas are essential partners in this interaction. On the other hand, C3G, Abi1 or Cbl knock-down impaired adhesion to fibronectin, while p130Cas silencing enhanced it. C3G, Cbl and p130Cas-SH3-b domains interact directly with common proteins involved in the regulation of cell adhesion and migration. Immunoprecipitation and immunofluorescence studies revealed that C3G form complexes with the FA proteins paxillin and FAK and their phosphorylated forms. Additionally, C3G, Abi1, Cbl and p130Cas regulate the expression and phosphorylation of paxillin and FAK. p38 alpha MAPK also participates in the regulation of adhesion in chronic myeloid leukemia cells. It interacts with C3G, CrkL, FAK and paxillin and regulates the expression of paxillin, CrkL and a5 integrin, as well as paxillin phosphorylation. Moreover, double knock-down of C3G/p38 alpha decreased adhesion to fibronectin, similarly to the single silencing of one of these genes, either C3G or p38 alpha. These suggest that C3G and p38 alpha MAPK are acting through a common pathway to regulate cell adhesion in K562 cells, as previously described for the regulation of apoptosis. Conclusions: Our results indicate that C3G-p38 alpha MAPK pathway regulates K562 cell adhesion through the interaction with FA proteins and Bcr-Abl, modulating the formation of different protein complexes at FA.