SDF-1 Controls Pituitary Cell Proliferation through the Activation of ERK1/2 and the Ca2+-Dependent, Cytosolic Tyrosine Kinase Pyk2.

Stromal cell-derived factor-1 (SDF-1) is a chemokine of the CXC subfamily that exerts its effects via CXCR4, a G-protein-coupled receptor. CXCR4 is often expressed by tumor cells, and its activation causes tumor cell proliferation. Using GH4C1 cells, here we show that SDF-1 induced cell proliferation in a dose-dependent manner. Thus, we evaluated the intracellular signaling involved in this effect. SDF-1 increased cytosolic [Ca²⁺] and activated Pyk2, ERK1/2, and BK_Ca channels. To correlate these intracellular effectors with the proliferative activity of SDF-1, we inhibited their activity using BAPTA-AM (Ca²⁺ chelator), PD98059 (MEK inhibitor), salicylate (Pyk2 inhibitor), and TEA (K⁺ channel blocker). All these compounds reverted SDF-1-induced proliferation, suggesting the involvement of multiple intracellular pathways. To identify a possible crosstalk and a molecular ordering among these pathways, we tested these antagonists on SDF-1-dependent activation of ERK1/2, Pyk2, and BK_Ca channels. We report that the inhibition of [Ca²⁺] _i increase or the blockade of BK_Ca channel activity did not affect ERK1/2 activation by SDF-1; Pyk2 activation was purely Ca²⁺-dependent, not involving ERK1/2 or BK_Ca channels; and BK_Ca channel activity was antagonized by Pyk2 but not by ERK1/2 inhibitors. These data suggest that SDF-1-dependent increase of [Ca²⁺] _i activates Pyk2, which, in turn, regulates BK_Ca channel activity. Conversely, ERK1/2 activation is an independent phenomenon. In conclusion, we demonstrate that SDF-1 induces proliferation of GH4C1 cells, suggesting that the activation of CXCR4 may represent a novel regulatory mechanism for pituitary cell proliferation which may contribute to pituitary adenoma development. [ABSTRACT FROM AUTHOR]