title: Downregulation of Fer induces PP1 activation and cell-cycle arrest in malignant cells.
abstract: Fer is a nuclear and cytoplasmic intracellular tyrosine kinase. Herein we show that Fer is required for cell-cycle progression in malignant cells. Decreasing the level of Fer using the RNA interference (RNAi) approach impeded the proliferation of prostate and breast carcinoma cells and led to their arrest at the G0/G1 phase. At the molecular level, knockdown of Fer resulted in the activation of the retinoblastoma protein (pRB), and this was reflected by profound hypo-phosphorylation of pRB on both cyclin-dependent kinase CDK4 and CDK2 phosphorylation sites. Dephosphorylation of pRB was not seen upon the direct targeting of either CDK4 or CDK2 expression, and was only partially achieved by the simultaneous depletion of these two kinases. Amino-acid sequence analysis revealed two protein phosphatase 1 (PP1) binding motifs in the kinase domain of Fer and the association of Fer with the pRB phosphatase PP1alpha was verified using co-immunoprecipitation analysis. Downregulation of Fer potentiated the activation of PP1alpha and overexpression of Fer decreased the enzymatic activity of that phosphatase. Our findings portray Fer as a regulator of cell-cycle progression in malignant cells and as a potential target for cancer intervention.
authors.affiliation: The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: O
authors.initials: O
authors.lastname: Pasder
authors.forename: S
authors.initials: S
authors.lastname: Shpungin
authors.forename: Y
authors.initials: Y
authors.lastname: Salem
authors.forename: A
authors.initials: A
authors.lastname: Makovsky
authors.forename: S
authors.initials: S
authors.lastname: Vilchick
authors.forename: S
authors.initials: S
authors.lastname: Michaeli
authors.forename: H
authors.initials: H
authors.lastname: Malovani
authors.forename: U
authors.initials: U
authors.lastname: Nir
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D016193:G1 Phase / Q000502:physiology*; D006801:Humans; D008297:Male; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D054645:Protein Phosphatase 1; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D016192:Resting Phase, Cell Cycle / Q000502:physiology*
chemical_list: D034741:RNA, Small Interfering; C052602:proto-oncogene protein c-fes-fps; D011505:Protein-Tyrosine Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1