Elevated L-PGDS activity contributes to PMA-induced apoptosis concomitant with downregulation of PI3-K.
Recently we demonstrated the induction of apoptosis by the addition of recombinant lipocalin-type prostaglandin D(2) synthase (L-PGDS) to the culture medium of LLC-PK(1) cells. Because 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 phorbol 12-myristate 13-acetate (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, which led to the hypophosphorylation and activation of Bad. In addition, hypophosphorylation of retinoblastoma protein was also observed in response to L-PGDS-induced apoptosis. Cellular depletion of L-PGDS levels by using an antisense RNA strategy prevented PI3-K inactivation by phorbol ester and inhibited caspase-3 activation and apoptosis. We conclude that phorbol ester-induced apoptosis is mediated by L-PGDS phosphorylation and activation by PKC and is accompanied by inhibition of the PI3-K/PKB anti-apoptotic signaling pathways.
Ragolia
Louis
L
Cellular Biology Laboratory, Winthrop-University Hospital, 222 Station Plaza North, Suite 505-B, Mineola, NY 11501, USA. lragolia@winthrop.org
Palaia
Thomas
T
Paric
Enesa
E
Maesaka
John K
JK
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D019746:Intramolecular Oxidoreductases / Q000378:metabolism* / Q000502:physiology; D018374:LLC-PK1 Cells; D054834:Lipocalins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013552:Swine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D019746:Intramolecular Oxidoreductases; D054834:Lipocalins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013755:Tetradecanoylphorbol Acetate; C022466:prostaglandin R2 D-isomerase