Activation of FAK/PI3K/Rac1 Signaling Controls Actin Reorganization and Inhibits Cell Motility in Human Cancer Cells

Abstract

We have recently identified a specific signaling pathway that regulates actin reorganization in malignant human breast and prostate epithelial cells associated with FAK, PI-3K and Rac1 activation. Here we report that this pathway operates in MCF7 cells upon activation of membrane androgen receptors (mAR). Stimulation of mAR by the non-permeable testosterone-BSA conjugate resulted in early actin reorganization documented by quantitative measurements of actin dynamics and morphological analysis of microfilament organization. This effect was regulated by early phosphorylation of FAK and subsequent PI-3K and Rac1 activation. The functional role of this pathway was further shown in A375 melanoma cells. Treatment with the opioid antagonist α_s1 casomorphin resulted in rapid and potent actin remodeling in A375 cells, regulated by rapid activation of the FAK/PI-3K/Rac1 signaling. Pretreatment of both cell lines with the specific PI-3K inhibitor wortmannin blocked actin reorganization. Interestingly, wound healing assays revealed that testosterone-BSA and α _s1 casomorphin significantly inhibited MCF7 and A375 cell motility respectively. These effects were abrogated through blockade of PI-3K signaling by wortmannin. The results presented here indicate that actin reorganization through FAK/PI3-K/Rac-1 activation operates in various human cancer cell systems supporting a functional role for FAK/PI-3K/Rac1/actin signaling in controlling cell motility.

Testosterone induced apoptosis in colon cancer cells is regulated by PI3K/Rac1 signaling

“…Testosterone-induced rapid Rac1/Cdc42 activation has been also reported in the past in both prostate and breast tumor cells. 4,5 On the other hand, in DU145 prostate cancer cells, Rac1 activation was not observed, while the involvement of the RhoA/B/ROCK signaling was reported to be crucial for the regulation of actin restructuring and the potent pro-apoptotic response. 7 These findings further emphasize the central role of the family of small GTPases in regulating actin redistribution triggered by mAR activation in tumors.…”

“…8,15 Furthermore, it was shown that mAR activation induced profound apoptotic regression of prostate and colon cancer cells in vitro and in mouse xenograftsin vivo 2,6,12,13 and suppressed cell growth and motility. 5,6,13,14 These effects were regulated by the mAR-governed actin reorganization. 7,12,13 Taken together, these studies clearly established that functional mARs trigger strong antitumorigenic effects, implying a potential role of mAR as a novel target for the development of selective cancer treatments.…”

“…1 Functional membrane androgen binding sites have been previously identified and characterized in human prostate and breast cancer cells. [2][3][4][5][6][7] Activation of these binding sites by no permeable testosterone albumin conjugates (TACs), was shown to induce strong proapoptotic and anti-tumorigenic effects on various tumors both in vitro and in vivo. 2,6,8,9 The molecular mechanisms governing these effects have been elucidated and specific signaling cascades triggered by the stimulation of membrane androgen receptors (mARs) have been described in prostate and breast tumor cells.…”

“…2,6,8,9 The molecular mechanisms governing these effects have been elucidated and specific signaling cascades triggered by the stimulation of membrane androgen receptors (mARs) have been described in prostate and breast tumor cells. 4,5,[9][10][11] Functional membrane androgen binding sites have been also reported in colon cancer cells and tissues. 12,13 Their activation by testosterone conjugates induced potent pro-apoptotic responses.…”

Membrane androgen receptor activation in prostate and breast tumor cells: Molecular signaling and clinical impact

“…Most recently, membrane androgen receptors transmitting rapid androgen signals have been characterized biochemically in several cell types including macrophages and T cells (8,19), LNCaP (9), T47D (15), MCF7 (20), DU145 (21), C6 (22), PC12 (23), or VSMC cells (24). Signals emanating from this receptor result in increased intracellular [Ca 21 ] and inositol 1,4,5-triphosphate formation, cannot be blocked by anti-androgens (9,25) and are sensitive to pertussis toxin inhibition indicating that mAR may actually be a GPCR (14)(15)(16).…”