Interaction of STAT6 with its co-activator SRC-1/NCoA-1 is regulated by dephosphorylation of the latter via PP2A

Targeting STATs in neuroinflammation: The road less traveled!

JAK/STAT transduction pathway is a highly conserved pathway implicated in regulating cellular proliferation, differentiation, survival and apoptosis. Dysregulation of this pathway is involved in the onset of autoimmune, haematological, oncological, metabolic and neurological diseases. Over the last few years, the research of anti-neuroinflammatory agents has gained considerable attention. The ability to diminish the STAT-induced transcription of inflammatory genes is documented for both natural compounds (such as polyphenols) and chemical drugs. Among polyphenols, quercetin and curcumin directly inhibit STAT, while Berberis vulgaris L. and Sophora alopecuroides L extracts act indirectly. Also, the Food and Drug Administration has approved several JAK/STAT inhibitors (direct or indirect) for treating inflammatory diseases, indicating STAT can be considered as a therapeutic target for neuroinflammatory pathologies. Considering the encouraging data obtained so far, clinical trials are warranted to demonstrate the effectiveness and potential use in the clinical practice of STAT inhibitors to treat inflammation-associated neurodegenerative pathologies.

Regulation of progesterone receptor activity by cyclin dependent kinases 1 and 2 occurs in part by phosphorylation of the SRC-1 carboxyl-terminus

We described previously a novel role for cyclin A2/Cdk2 as a progesterone receptor (PR) coactivator. In reporter gene assays, cyclin A2 overexpression enhanced PR activity while inhibition of Cdk2 activity using the chemical inhibitor roscovitine or Cdk2 siRNA strongly inhibited PR activity. We demonstrate here that both Cdk1 and Cdk2 contribute to maximal induction of endogenous progestin responsive genes in T47D breast cancer cells. Our earlier studies suggested that the mechanism by which cyclin A2/Cdk2 enhances PR activity is via phosphorylation of steroid receptor coactivator-1 (SRC-1), which increases PR-SRC-1 interactions. To assess the importance of SRC-1 phosphorylation in the regulation of PR activity, SRC-1 was phosphorylated by cyclin A2/Cdk2 in vitro and seventeen phosphorylation sites were identified using biochemical techniques. We show that one of these sites, T1426 (adjacent to the C-terminal LXXLL nuclear receptor interaction motif), is an in vivo target of Cdks in mammalian cells and an in vitro target of Cdk1 and Cdk2. Phosphorylation of T1426 also contributes to SRC-1 coactivation potential, as mutation of the threonine target site to alanine results in reduced stimulation of PR activity by SRC-1. Together, these results suggest a role for Cdk1 and Cdk2 in the regulation of endogenous PR activity in part through phosphorylation of SRC-1.