Involvement of protein kinase PKN1 in G2/M delay caused by arsenite.

PKN1 is a serine/threonine protein kinase that has been reported to mediate cellular response to stress. We show here that in response to arsenite exposure, PKN1 kinase activity was stimulated, which was associated with increased binding of PKN1 to Cdc25C and delayed mitotic entry. A role for PKN1 in mediating arsenite-induced G(2)/M delay was supported by the finding that expression of a constitutively active form of PKN1 (PKN1AF3) in HeLa cells delayed the mitotic entry of cell cycle. Further experiments indicate that PKN1 directly phosphorylated serine 216 (Ser216) in Cdc25C, which then facilitated association between Cdc25C and 14-3-3. Significantly, expression of a phosphorylation mutant of Cdc25C (S216A) partially abrogated the cell-cycle arrest in response to arsenite. Together, our results suggest that PKN1 mediates arsenite-induced delay of the G(2)/M transition by binding to and phoshorylating Cdc25C. Copyright 2005 Wiley-Liss, Inc.