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 PP1α was verified using co-immunoprecipitation analysis. Downregulation of Fer potentiated the activation of PP1α 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.
Bibliographical noteFunding Information:
We thank Ms Sharon Victor for typing this manuscript and Mr Uri Karo for assistance with the flow-cytometry analysis. This work was supported by grants from CaPCURE Israel, the Ministry of Health Chief Scientist’s Research Fund, Deborah Silin and Samuel-Heinrich Winograd Research Fund, the Weinkselbaum Family Research Fund, and a grant from the Horowitz Foundation.
- Fer kinase
- Malignant cells