Protein kinase Cι promotes UBF1–ECT2 binding on ribosomal DNA to drive rRNA synthesis and transformed growth of non-small-cell lung cancer cells

Abstract

Epithelial cell–transforming sequence 2 (ECT2) is a guanine nucleotide exchange factor for Rho GTPases that is overexpressed in many cancers and involved in signal transduction pathways that promote cancer cell proliferation, invasion, and tumorigenesis. Recently, we demonstrated that a significant pool of ECT2 localizes to the nucleolus of non-small-cell lung cancer (NSCLC) cells, where it binds the transcription factor upstream binding factor 1 (UBF1) on the promoter regions of ribosomal DNA (rDNA) and activates rDNA transcription, transformed cell growth, and tumor formation. Here, we investigated the mechanism by which ECT2 engages UBF1 on rDNA promoters. Results from ECT2 mutagenesis indicated that the tandem BRCT domain of ECT2 mediates binding to UBF1. Biochemical and MS-based analyses revealed that protein kinase Cι (PKCι) directly phosphorylates UBF1 at Ser-412, thereby generating a phosphopeptide-binding epitope that binds the ECT2 BRCT domain. Lentiviral shRNA knockdown and reconstitution experiments revealed that both a functional ECT2 BRCT domain and the UBF1 Ser-412 phosphorylation site are required for UBF1-mediated ECT2 recruitment to rDNA, elevated rRNA synthesis, and transformed growth. Our findings provide critical molecular insight into ECT2-mediated regulation of rDNA transcription in cancer cells and offer a rationale for therapeutic targeting of UBF1- and ECT2-stimulated rDNA transcription for the management of NSCLC.

New Mechanisms Underlying Oncogenesis in Dbl Family Rho Guanine Nucleotide Exchange Factors

“…For example, PKC-mediated phosphorylation of cytoplasmic Ect2 on Thr328 within the autoinhibitory linker led to activation of the oncogenic Rac1-Pak-Mek1,2-Erk1,2 pathway and PKC-mediated phosphorylation of nuclear Ect2 stimulated Rac1-dependent ribosomal DNA (rDNA) transcription. (Justilien et al, 2017;Justilien and Fields, 2009;Justilien et al, 2011;Justilien et al, 2020). Similarly, Ect2 mislocalization association has been reported in ovarian and colorectal cancers (Cook et al, 2022;Huff et al, 2013).…”

Epithelial cell transforming factor ECT2 is an important regulator of DNA double-strand break repair and genome stability

“…Increasing evidence, including our previous study, indicates that dysregulated ECT2 activity is implicated in many types of cancer and that ECT2 depletion suppresses tumorigenesis ( 35 , 41 , 52 , 53 ). These findings suggest that ECT2 acts as an oncogenic protein.…”

Copy number variations and protein expression of Cyclin E1 and Epithelial cell transforming sequence 2 genes predict the chemotherapeutic response in patients with serous ovarian carcinoma

“…Contrary to this finding, most of the studies reported ECT2 as a marker of bad prognosis in solid malignancies. 11,25 Despite many molecular updates for ovarian carcinomas in the literature, still the overall survival of the patients is poor worldwide while it is graves in our part of the world. Copy number variations are lately been emphasized for their role in potential prognostication of SOC patients in different studies.…”