Evidence for phosphatase activity of p27SJ and its impact on the cell cycle

Nune Darbinian, Marta Czernik, Armine Darbinyan, Mikael Elias, Eric Chabriere, Surekha Bonasu, Kamel Khalili, Shohreh Amini

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


p27SJ, a novel protein isolated from St John's wort (Hypericum perforatum), belongs to an emerging family of DING proteins that are related to a prokaryotic phosphate-binding protein superfamily. Here we demonstrate that p27SJ exhibits phosphatase activity and that its expression in cells decreases the level of phosphorylated Erk1/2, a key protein of several signaling pathways. Treatment of p27SJ-expressing cells with phosphatase inhibitors including okadaic acid, maintained Erk1/2 in its phosphorylated form, suggesting that dephosphorylation of Erk1/2 is mediated by p27SJ. Further, expression of p27SJ affects Erk1/2 downstream regulatory targets such as STAT3 and CREB. Moreover, the level of expression of cyclin A that associates with active ERK1/2 and is regulated by CREB, was modestly reduced in p27SJ-expressing cells. Accordingly, results from in vitro kinase assays revealed a noticeable decrease in the activity of cyclin A in cells expressing p27SJ. Cell cycle analysis demonstrated dysregulation at S and G2/M phases in cells expressing p27SJ, supporting the notion that a decline in cyclin A activity by p27SJ has a biological impact on cell growth. These observations provide evidence that p27SJ alters the state of Erk1/2 phosphorylation, and impacts several biological events associated with cell growth and function. J.

Original languageEnglish (US)
Pages (from-to)400-407
Number of pages8
JournalJournal of Cellular Biochemistry
Issue number3
StatePublished - Jun 1 2009


  • Ding family
  • Phosphatase activity
  • p27SJ


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