Purpose: The Src family kinase Fyn, heterogenous nuclear ribonucleoprotein (HnRNP) A2B1 and Sam68 are thought to be associated with the metastasis of tumors, but their roles in the regulation of apoptosis remain unclear. This study investigated the role of Fyn and its potential relationship with HnRNPA2B1 and Sam68 in the regulation of apoptosis in pancreatic cancer. Experimental design. We examined both the activity of Fyn and the expression of HnRNPA2B1 in human pancreatic cancer tissues and systematically investigated the apoptotic mechanisms induced by Fyn activity using multiple experimental approaches.
Results: We found that Fyn activity was increased in metastatic pancreatic cancer tissues. In the pancreatic cancer BxPc3 cell line, the inhibition of Fyn activity by kinase-dead Fyn downregulated HnRNPA2B1 expression. Further analysis showed that HnRNPA2B1 expression was associated with pancreatic cancer progression. In BxPc3 cells, HnRNPA2B1 bound to Bcl-x messenger RNA (mRNA), which affected splicing and therefore, the formation of Bcl-x(s). Downregulation of HnRNPA2B1 by RNA interference (RNAi) resulted in the increased formation of the pro-apoptotic Bcl-x(s) and promoted apoptosis of BxPc3 cells. In addition, deactivation of Fyn in BxPc3 cells reduced Sam68 phosphorylation. This resulted in increased binding between Sam68 and Bcl-x mRNA, promoting the formation of the anti-apoptotic Bcl-x(L). The knockdown of Sam68 by RNAi also increased the formation of Bcl-x(L). Finally, HnRNPA2B1 overexpression or Sam68 knockdown could rescue pancreatic cancer cells from apoptosis.
Conclusion: Our results suggest a mechanism by which Fyn requires HnRNPA2B1 and Sam68 to coordinate and regulate apoptosis, thus promoting the proliferation and metastasis of pancreatic cancer.