Protein Kinase Cδ Is Required for Survival of Cells Expressing Activated p21

Abstract

Inhibition of protein kinase C (PKC) activity in transformed cells and tumor cells containing activated p21RAS results in apoptosis. To investigate the pro-apoptotic pathway induced by the p21 RAS oncoprotein, we first identified the specific PKC isozyme necessary to prevent apoptosis in the presence of activated p21RAS . Dominant-negative mutants of PKC, short interfering RNA vectors, and PKC isozyme-specific chemical inhibitors directed against the PKC␦ isozyme demonstrated that PKC␦ plays a critical role in p21 RAS -mediated apoptosis. An activating p21 RAS mutation, or activation of the phosphatidylinositol 3-kinase (PI3K) Ras effector pathway, increased the levels of PKC␦ protein and activity in cells, whereas inhibition of p21 RAS activity decreased the expression of the PKC␦ protein. Activation of the Akt survival pathway by oncogenic Ras required PKC␦ activity. Akt activity was dramatically decreased after PKC␦ suppression in cells containing activated p21RAS . Conversely, constitutively activated Akt rescued cells from apoptosis induced by PKC␦ inhibition. Collectively, these findings demonstrate that p21 RAS , through its downstream effector PI3K, induces PKC␦ expression and that this increase in PKC␦ activity, acting through Akt, is required for cell survival. The p21 RAS effector molecule responsible for the initiation of the apoptotic signal after suppression of PKC␦ activity was also determined to be PI3K. PI3K (p110 CAAX , where AA is aliphatic amino acid) was sufficient for induction of apoptosis after PKC␦ inhibition. Thus, the same p21 RAS effector, PI3K, is responsible for delivering both a pro-apoptotic signal and a survival signal, the latter being mediated by PKC␦ and Akt. Selective suppression of PKC␦ activity and consequent induction of apoptosis is a potential strategy for targeting of tumor cells containing an activated p21 RAS .The ras oncogene family is among the most commonly mutated group of genes in human cancer. Its protein products code for three closely related p21 RAS proteins, including H-Ras, K-Ras, and N-Ras. p21RAS proteins are localized in the inner plasma membrane, bind GDP and GTP, and possess an intrinsic GTPase activity. p21RAS proteins function as plasma membrane-bound guanine nucleotide-binding proteins and act as molecular switches, thereby regulating signal transduction pathways for hormones, growth factors, and cytokine receptors (1). Several downstream effector proteins of p21 RAS have been identified that bind preferentially to p21 RAS in the GTP-bound state, including Raf, phosphatidylinositol 3-kinase (PI3K), 2 and a family of GDP-GTP exchange factors for the Ral small GTPases (Ral-GDS). Raf proteins, which are proto-oncogeneencoded serine/threonine kinases, activate the MEK-ERK signaling pathway. PI3K activation results in the activation of the anti-apoptotic serine/threonine kinase Akt, among other molecules. Other p21 RAS targets include the GTPase-activating proteins, p120 GAP and neurofibromin (2). p21 RAS proteins were shown to influence proliferation, d...

K-Ras4B phosphorylation at Ser181 is inhibited by calmodulin and modulates K-Ras activity and function

“…Our results strongly suggest that phosphorylation of K-RasG12V is important to stimulate transformation, mobility, apoptosis resistance upon adriamycin treatment and to favor proliferation and survival at low growth factor concen- Calmodulin inhibits K-Ras phosphorylation B Alvarez-Moya et al tration. Our data agree with the fact that in some tumor cell lines, such as MIA-PaCa2 or HCT116, PKC activity stimulates cell survival and proliferation provided that K-RaG12V is expressed (Liou et al, 2004) or with some other reports in which it was demonstrated that PKC functions as a critical anti-apoptotic signal transducer in cells containing activated K-Ras, promoting cell survival through PI3K/PDK1/AKT pathway (Xia et al, 2007(Xia et al, , 2009. In contrast to previously published data (Bivona et al, 2006), phospho-mimetic K-Ras expression did not induce apoptosis in our cell lines.…”

Protein Kinase Cδ Supports Survival of MDA-MB-231 Breast Cancer Cells by Suppressing the ERK1/2 Pathway

“…Furthermore, PKC␦ has been shown to support survival by inducing activation of Akt in cells with a constitutively activated Ras pathway (29). These data together indicate that Akt may be a mediator of the PKC␦ effects.…”

“…It has been reported that PKC␦ is required for survival of mouse fibroblasts with mutated constitutively activated Ras by mediating Akt activation (29). Furthermore, ERK1/2 has been shown to suppress Akt phosphorylation in many breast cancer cell lines (28).…”

Protein Kinase C-δ Mediates Neuronal Apoptosis in the Retinas of Diabetic Rats via the Akt Signaling Pathway

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