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

J Biol Chem. 2020 Jun 12;295(24):8214-8226. doi: 10.1074/jbc.RA120.013175. Epub 2020 Apr 29.


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.

Keywords: cancer biology; cell proliferation; epithelial cell transforming protein 2 (ECT2); gene regulation; non-small cell lung cancer; protein kinase C ι (PKCι); protein-protein interaction; ribosomal DNA transcription; ribosomal ribonucleic acid (rRNA) (ribosomal RNA); ribosome biogenesis; tumor cell biology; upstream binding factor 1 (UBF1).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Carcinoma, Non-Small-Cell Lung / metabolism*
  • Carcinoma, Non-Small-Cell Lung / pathology
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Transformation, Neoplastic / metabolism*
  • Cell Transformation, Neoplastic / pathology
  • DNA, Ribosomal / metabolism*
  • Humans
  • Isoenzymes / metabolism*
  • Lung Neoplasms / metabolism*
  • Lung Neoplasms / pathology
  • Models, Biological
  • Phosphopeptides / metabolism
  • Phosphorylation
  • Pol1 Transcription Initiation Complex Proteins / metabolism*
  • Protein Binding
  • Protein Domains
  • Protein Kinase C / metabolism*
  • Proto-Oncogene Proteins / chemistry
  • Proto-Oncogene Proteins / metabolism*
  • RNA, Ribosomal / metabolism*


  • DNA, Ribosomal
  • ECT2 protein, human
  • Isoenzymes
  • Phosphopeptides
  • Pol1 Transcription Initiation Complex Proteins
  • Proto-Oncogene Proteins
  • RNA, Ribosomal
  • transcription factor UBF
  • Protein Kinase C
  • protein kinase C lambda