title: The tumor suppressive role of eIF3f and its function in translation inhibition and rRNA degradation.
abstract: Deregulated translation plays an important role in human cancer. We previously reported decreased eukaryotic initiation factor 3 subunit f (eIF3f) expression in pancreatic cancer. Whether decreased eIF3f expression can transform normal epithelial cells is not known. In our current study, we found evidence that stable knockdown of eIF3f in normal human pancreatic ductal epithelial cells increased cell size, nuclear pleomorphism, cytokinesis defects, cell proliferation, clonogenicity, apoptotic resistance, migration, and formation of 3-dimensional irregular masses. Our findings support the tumor suppressive role of eIF3f in pancreatic cancer. Mechanistically, we found that eIF3f inhibited both cap-dependent and cap-independent translation. An increase in the ribosomal RNA (rRNA) level was suggested to promote the generation of cancer. The regulatory mechanism of rRNA degradation in mammals is not well understood. We demonstrated here that eIF3f promotes rRNA degradation through direct interaction with heterogeneous nuclear ribonucleoprotein (hnRNP) K. We showed that hnRNP K is required for maintaining rRNA stability: under stress conditions, eIF3f dissociates hnRNP K from rRNA, thereby preventing it from protecting rRNA from degradation. We also demonstrated that rRNA degradation occurred in non-P body, non-stress granule cytoplasmic foci that contain eIF3f. Our findings established a new mechanism of rRNA decay regulation mediated by hnRNP K/eIF3f and suggest that the tumor suppressive function of eIF3f may link to impaired rRNA degradation and translation.
authors.affiliation: Department of Pathology, Department of Surgery, The University of Arizona Cancer Center, University of Arizona, Tucson, Arizona, United States of America.
authors.forename: Fushi
authors.initials: F
authors.lastname: Wen
authors.forename: Renyuan
authors.initials: R
authors.lastname: Zhou
authors.forename: Alex
authors.initials: A
authors.lastname: Shen
authors.forename: Andrew
authors.initials: A
authors.lastname: Choi
authors.forename: Diana
authors.initials: D
authors.lastname: Uribe
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Shi
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers; D039621:Eukaryotic Initiation Factor-3 / Q000235:genetics / Q000502:physiology*; D016147:Genes, Tumor Suppressor; D006801:Humans; D014176:Protein Biosynthesis / Q000502:physiology*; D012335:RNA, Ribosomal / Q000235:genetics / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D039621:Eukaryotic Initiation Factor-3; D012335:RNA, Ribosomal; C096013:EIF3I protein, human