Gα_i2 Induces Cell Migration in PC3 Prostate Cancer Cells in the Absence of Rac1 Activation

Metastatic prostate cancer occurs when the tumor spreads from the prostate gland to other parts of the body. Previous studies have shown that Gα_i2, a subunit of the heterotrimeric G protein complex, plays a critical role in inducing cell migration and invasion in prostate cancer cells in response to diverse stimuli. Rac1 is a small rho-GTPase, which is activated by the phosphoinositide 3-kinase (PI3K)/AKT pathway and plays an essential role during cell migration. Previous studies have shown that the knockdown of Gα_i2 attenuates cell migration without causing any reduction in basal Rac1 activity in both PC3 and DU145 cells, and has only marginal effects on the epidermal growth facotor (EGF)-induced increase in Rac1 activity. Therefore, Gα_i2 may be involved in the regulation of cell motility and invasion independently or downstream of Rac1 activation. In this study, we investigated the possible mechanism of Gα_i2 at the level of the Rac1-dependent activation of Wiskott-Aldrich Syndrome Protein)-family verprolin homologous protein2 (Wave2) and actin related protein 2/3 (Arp 2/3) proteins, downstream effectors of activated Rac1. PC3 cells with a stable overexpression of constitutively active Rac1 were transfected with control siRNA or Gα_i2 siRNA to knockdown endogenous Gα_i2 expression. Western blot analysis showed that the Rac1-dependent activation of Wave2 was impaired in the absence of Gα_i2. The overexpression of constitutively active Gα_i2 (Gα_i2-Q205L) in PC3 cells significantly increased cell migration compared to cells transfected with control plasmids. In the parallel experiments, a specific Gα_i2 inhibitor blocked G_iα2-Q205L-induced cell migration in PC3 cells. Furthermore, the Rac1 inhibitor did not block increased cell migration in PC3 cells overexpressing constitutively active Gα_i2. We conclude that activated Gα_i2 plays a crucial role in cell migration in prostate cancer cells independent of Rac1 activation.