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Articles in PresS, published online ahead of print September 11, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00247.2002
Submitted on May 29, 2002
Accepted on December 31, 1969
1 Cell Biology, Winthrop-University Hospital, Mineola, NY, USA; Medicine, Stony Brook University, Stony Brook, NY, USA
2 Cell Biology, Winthrop-University Hospital, Mineola, NY, USA
* To whom correspondence should be addressed. E-mail: lragolia{at}winthrop.org.
Recently, we demonstrated the induction of apoptosis by the addition of recombinant prostaglandin D2 synthase (L-PGDS) to the culture medium of LLC-PK1 cells. Since protein kinase C (PKC) has been shown to be involved in the apoptotic process of various cell types, we examined the potential role of L-PGDS in PMA-induced apoptosis. We report here the enzymatic activation and phosphorylation of L-PGDS, in response to phorbol ester in cell culture, and the direct phosphorylation of recombinant L-PGDS by PKC in vitro. Treatment of cells with PMA or L-PGDS, decreased phosphatidylinositol 3-kinase (PI3-K) activity and concomitantly inhibited protein kinase B (PKB/Akt) phosphorylation, leading to the hypophosphorylation and activation of Bad. In addition, hypophosphorylation of retinoblastoma protein (pRb) was also observed in response to L-PGDS-induced apoptosis. Cellular depletion of L-PGDS levels, using an antisense RNA strategy, prevented PI3-K inactivation by phorbol ester and inhibited caspase3 activation and apoptosis. We conclude that phorbol ester-induced apoptosis is mediated by L-PGDS phosphorylation and activation by PKC, and is accompanied by an inhibition of the PI3-K/PKB anti-apoptotic signaling pathways.
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