Abstract LB-113: PKC-iota induces uncontrolled glioblastoma cell survival by modulating proapoptotic function of Bad

Abstract

Abstract Brain tumors are a major challenge since they destroy the most important part of the human body. The aggressive and infiltrative behavior is a hallmark of glioblastoma multiforme which makes it highly incurable. PKC-iota is reported to be highly expressed in transformed phenotype of human glioma, benign and malignant meningiomas (Cell Prolif. 41:122-35, 2008) but the signaling mechanism by which PKC-iota induces glioma cell survival remains elusive. Hence, in the current study, we investigated whether PKC-iota phosphorylates and de-activates Bad, a pro-apoptotic BH3-only molecule of the Bcl-2 family. Our results demonstrated that PKC-iota co-localizes as well as directly associates and phosphorylates Bad at Ser-112, Ser-136 and Ser-155. In addition, recombinant PKC-iota induced direct phosphorylation of exogenous as well as endogenous Bad at all three serine residues as shown by in-vitro kinase assay. Recombinant PKC-zeta (is 70% homologous to PKC-iota) and PKC-delta (known to regulate the activity of Bad in rat cardiac myocytes; Mol Cells. 24:224-231, 2007) in contrast phosphorylated Bad only at Ser-112 residue in in-vitro kinase assays. Reduction of PKC-iota upon RNA interference exhibited a corresponding reduction in Bad phosphorylation at these three sites. Conversely, inhibition of PKC-zeta and delta by their corresponding siRNA did not lead to reduction of Bad phosphorylation. Additionally, disruption of Bad/Bcl-XL heterodimerization was not observed in either of the RNA silenced samples. Thus, our data strongly supports the hypothesis that PKC-iota may function as a Bad kinase directly inhibiting its pro-apoptotic function and impeding the normal homeostasis of glioma cells thereby enhancing prolonged survival of glioma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-113.