Molecular mechanisms of basic fibroblastic growth factor upregulates connexin43 expression in the human glioblastoma cells

Decreasing Connexin43 (Cx43) expression and dysfunction of gap junction intercellular communication (GJIC) is associated with increasing proliferation and the grade of human glioma cells. Our group has previously reported that bFGF knockdown interferes connexin43 expression, however, the mechanisms underlying this interference remain unknown. We hypothesized that the bFGF signaling pathway may activate gene Cx43, and identified the signal pathway involved in bFGF-induced Cx43 expression. In the present study, we revealed that bFGF stimulates expression of Cx43 gene and that this stimulation is time-dependent. Conversely, knocking down bFGF levels using LV-bFGF-siRNA can significantly decrease both Cx43 gene and p-Cx43 expression in glioma cell line LN229. Furthermore, presence of both AG490 (STAT3 antagonist), as well as PD0325901 (inhibitor of ERK1/2 pathway) inhibited expression of gene Cx43 via blocking the bFGF stimulation effect over Cx43. This finding suggests that bFGF-induced Cx43 expression is regulated mainly via activation of STAT3 and ERK1/2 but not AKT pathway. Further, LV-bFGF-siRNA can decrease the Cx43 expression and aggravate GJIC in LN229 glioma cell. Also, Cx43 is found within the cytoplasm and nuclear membrane of LN229 cells, unlike U251 cell lines. This subcellular distribution is decreased by LV-bFGF-siRNA. The results of our study suggest that bFGF upregulates Cx43 and p-Cx43 (Ser368) expression in LN229 cell. We have indirect evidence that this upregulation occurs via the STAT3 and ERK1/2 pathway. Our study also shows that Cx43 expression and subcellular distribution in glioma cells is highly heterogeneous.