RACK1 Regulates G₁/S Progression by Suppressing Src Kinase Activity

Abstract

Cancer genes exert their greatest influence on the cell cycle by targeting regulators of a critical checkpoint in late G 1 . Once cells pass this checkpoint, they are fated to replicate DNA and divide. Cancer cells subvert controls at work at this restriction point and remain in cycle. Previously, we showed that RACK1 inhibits the oncogenic Src tyrosine kinase and NIH 3T3 cell growth. RACK1 inhibits cell growth, in part, by prolonging G 0 /G 1 . Here we show that RACK1 overexpression induces a partial G 1 arrest by suppressing Src activity at the G 1 checkpoint. RACK1 works through Src to inhibit Vav2, Rho GTPases, Stat3, and Myc. Consequently, cyclin D1 and cyclin-dependent kinases 4 and 2 (CDK4 and CDK2, respectively) are suppressed, CDK inhibitor p27 and retinoblastoma protein are activated, E2F1 is sequestered, and G 1 /S progression is delayed. Conversely, downregulation of RACK1 by short interference RNA activates Src-mediated signaling, induces Myc and cyclin D1, and accelerates G 1 /S progression. RACK1 suppresses Src-but not mitogen-activated protein kinasedependent platelet-derived growth factor signaling. We also show that Stat3 is required for Rac1 induction of Myc. Our results reveal a novel mechanism of cell cycle control in late G 1 that works via an endogenous inhibitor of the Src kinase.

Centrosome aberrations and G1 phase arrest after in vitro and in vivo treatment with the SRC/ABL inhibitor dasatinib

“…Consequently, the inhibition of SRC results in kinaseinactive SRC inducing a G1/S block and delayed G1/S transition. [45][46][47][48] However, SRC inhibitors induced dosedependent anemia, edema and erythema and affected the ovaries and liver in rats. 49 Limited enzymatic selectivity, which is not correlated to the compound's core structure and which led to inhibition of other kinases in non-targeted tissues, may be possible.…”

RACK1 and Stratifin Target ΔNp63α for a Proteasome Degradation in Head and Neck Squamous Cell Carcinoma Cells upon DNA Damage

“…RACK1 was also recently implicated into a regulation of G 1 /S progression by binding to Src and suppressing its kinase activity, while use of siRNA for RACK1 activated Src-mediated signaling, induced myc and cyclin D1 and accelerated G1/S progression. 54 Numerous reports shown that MDM2 family members function as E3 ubiquitin ligases that mediate monoubiquitination of p53, its export from nucleus to cytoplasm and then targeting it into a proteasome machinery. [55][56][57] However, other proteins (e.g., COP1, PIRH2) were found to interact with p53 and might also perform this function.…”

A novel pro-apoptotic function of RACK1: suppression of Src activity in the intrinsic and Akt pathways

“…Using a yeast two-hybrid assay, we identified RACK1 as a novel substrate and binding partner of Src and an endogenous inhibitor of Src kinase activity and cell growth (Chang et al, 1998(Chang et al, , 2001(Chang et al, , 2002. We showed that RACK1 exerts its effect on colonic cell growth, in part by suppressing Src activity at G 1 and mitotic checkpoints (Mamidipudi et al, 2004a(Mamidipudi et al, , 2007. We hypothesize that RACK1 regulates other aspects of cell growth.…”

“…Earlier we showed that RACK1 regulates colonic cell growth, in part by suppressing Src activity at G 1 and mitotic checkpoints (Mamidipudi et al, 2004a(Mamidipudi et al, , 2007. Another potential mechanism by which RACK1 could regulate growth is by inducing apoptosis.…”