G protein coupled receptor kinase 5 modifies the nucleolar stress response activated by actinomycin D

Abstract

G protein coupled receptor kinase 5 (GRK5) is localized within the nucleus to moderate functions such as DNA transcription, in addition to its localization at the plasma membrane. In this report, we show that GRK5 modifies the nucleolar stress response activated by the DNA polymerase inhibitor, Actinomycin D (ActD). We showed an increased sensitivity to the apoptotic effects of ActD on cervical HeLa and the breast cancer cell line MDA MB 231 with reduced GRK5 protein expressions. Furthermore, the rate of response to ActD varied between the two types of breast cancer cells tested, MDA MB 231 and MCF7 cells, since they have innate differences in GRK5 protein expressions. During the early ActD treatment period, GRK5 phosphorylates nucleophosmin (NPM1) at T199 before and during treatment. Phosphorylation at this site increases the ability of NPM1 to interact with p14ARFin vitro, which may affect p14ARF protein expression levels. Expression levels are lower in control shRNA transfected cells but higher in GRK5 shRNA transfected cells. Collectively, this suggests that GRK5 modifies the nucleolar stress response associated with ActD.