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Phoshorylation regulated UBF1 and ECT2 Binding on ribosomal DNA

ABSTRACT: Epithelial Cell Transforming Sequence 2 (ECT2), a guanine nucleotide exchange factor (GEF) for Rho GTPases, is overexpressed in many cancers and is 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 the ribosomal DNA (rDNA) and activates rDNA transcription, transformed growth and tumor formation. Here we investigate the mechanism by which ECT2 engages UBF1 on rDNA. Mutagenesis of ECT2 demonstrates that the tandem BRCT domain of ECT2 mediates binding to UBF1. Biochemical and mass spectrometry analysis reveals that Protein Kinase Ci (PKCi) directly phosphorylates UBF1 at Ser412 to generate a phosphopeptide binding epitope that binds the ECT2 BRCT domain. Lentiviral shRNA knockdown and reconstitution experiments demonstrate that both a functional ECT2 BRCT domain and the UBF1 Ser412 phosphorylation site are required for UBF1 mediated ECT2 recruitment to rDNA, elevated rRNA synthesis and transformed growth. Taken together, our study provides new molecular insight into ECT2 mediated regulation of rDNA transcription in cancer cells and provides a rationale for therapeutic targeting of UBF1 and ECT2 stimulated rDNA transcription for the treatment of NSCLC.

INSTRUMENT(S): Q Exactive Plus

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Alan P. Fields

PROVIDER: MSV000085269 | MassIVE | Fri Apr 10 08:41:00 BST 2020

REPOSITORIES: MassIVE

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