Abstract A11: Oncogenic Ras signaling involves sustained perinuclear localization of the effector kinases p-ERK1/2 and CK2 via KSR-1 and endosomal trafficking

Abstract

Abstract In primary cells oncogenic Ras can induce cellular senescence, an important tumor suppression mechanism that must be bypassed in tumor cells. Oncogene-induced senescence is regulated in part by the transcription factor C/EBPβ, which is post-translationally activated by Ras signaling. We previously reported that C/EBPβ activation by H-RasV12 is suppressed in immortalized and transformed cells by a novel 3'UTR-dependent mechanism termed 3'UTR regulation of protein activity, or UPA. UPA acts by restricting the Cebpb mRNA to a peripheral cytoplasmic region, which is spatially distinct from a perinuclear compartment containing the C/EBPβ-activating kinase, p-ERK1/2. UPA can thereby block C/EBPβ phosphorylation/activation and suppress its pro-senescence functions in tumor cells. Here we identify CK2 as another C/EBPβ kinase that undergoes perinuclear relocalization in RasV12-expressing cells. Accordingly, CK2-mediated phosphorylation of C/EBPβ was inhibited by the Cebpb 3'UTR in tumor cells but not primary cells. The MAPK signaling scaffold KSR-1 and endocytic trafficking were both required for RasV12-induced activation of C/EBPβ and perinuclear targeting of p-ERK and CK2. CK2 co-localized and interacted with KSR-1 and Rab11 (a marker of recycling endosomes), while p-ERK appeared to be associated with a different endosomal population. RasV12 expression led to sustained perinuclear localization of p-ERK and CK2 in both transformed and senescent cells. In contrast, growth factors (GFs) only transiently induced this response, which occurred with delayed kinetics (4-6 hr) coinciding with transitory activation of C/EBPβ. Our results indicate that oncogenic Ras signaling involves constitutive activation of the delayed GF signaling phase, characterized by restriction of the effector kinases p-ERK and CK2 to perinuclear endosomes. In this compartment they can access critical targets such as C/EBPβ in a UPA-regulated manner to promote either transformation or senescence. Citation Format: Sook Lee, Sandip K. Basu, Vijay Walia, Deborah K. Morrison, Peter F. Johnson. Oncogenic Ras signaling involves sustained perinuclear localization of the effector kinases p-ERK1/2 and CK2 via KSR-1 and endosomal trafficking. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A11. doi: 10.1158/1557-3125.RASONC14-A11