Protein Phosphatase-1 Regulates Expression of Neuregulin-1

Abstract

Protein phosphatase 1 (PP1), a cellular serine/threonine phosphatase, is targeted to cellular promoters by its major regulatory subunits, PP1 nuclear targeting subunit, nuclear inhibitor of PP1 (NIPP1) and RepoMan. PP1 is also targeted to RNA polymerase II (RNAPII) by NIPP1 where it can dephosphorylate RNAPII and cycle-dependent kinase 9 (CDK9). Here, we show that treatment of cells with a small molecule activator of PP1 increases the abundance of a neuregulin-1 (NRG-1)-derived peptide. NRG-1 mRNA and protein levels were increased in the cells stably or transiently expressing mutant NIPP1 (mNIPP1) that does not bind PP1, but not in the cells expressing NIPP1. Expression of mNIPP1 also activated the NRG-1 promoter in an NF-κB-dependent manner. Analysis of extracts from mNIPP1 expressing cells by glycerol gradient centrifugation showed a redistribution of PP1 and CDK9 between large and small molecular weight complexes, and increased CDK9 Thr-186 phosphorylation. This correlated with the increased CDK9 activity. Further, RNAPII co-precipitated with mNIPP1, and phosphorylation of RNAPII C-terminal domain (CTD) Ser-2 residues was greater in cells expressing mNIPP1. In mNIPP1 expressing cells, okadaic acid, a cell-permeable inhibitor of PP1, did not increase Ser-2 CTD phosphorylation inhibited by flavopiridol, in contrast to the NIPP1 expressing cells, suggesting that PP1 was no longer involved in RNAPII dephosphorylation. Finally, media conditioned with mNIPP1 cells induced the proliferation of wild type 84-31 cells, consistent with a role of neuregulin-1 as a growth promoting factor. Our study indicates that deregulation of PP1/NIPP1 holoenzyme activates NRG-1 expression through RNAPII and CDK9 phosphorylation in a NF-κB dependent manner.

Protein Phosphatase-1 –targeted Small Molecules, Iron Chelators and Curcumin Analogs as HIV-1 Antivirals

“…NIPP1 can also activate transcription as it induces expression of mesenchymal genes in HeLa cells [41]. We recently reported that NIPP1 represses expression of neuregulin-1, a heparin-binding neurotrophic factor [42]. Thus, deregulation of PP1 can enhance transcription of normally repressed genes, including integrated HIV-1 provirus.…”

Recruitment of the protein phosphatase-1 catalytic subunit to promoters by the dual-function transcription factor RFX1

“…In this work, we show that PP1c is recruited to promoters by RFX1. PP1c dephosphorylates and subsequently affect the function of transcription factor as well as components of the general transcription machinery [33][34][35][36][37][38][39]. We suggest a model for the context dependent function of RFX1 which is achieved by recruiting PP1c to promoters leading to the de-phosphorylation of neighboring factors.…”