kappa-Opioid receptor potentiates apoptosis via a phospholipase C pathway in the CNE2 human epithelial tumor cell line

The mechanism by which kappa -opioid receptor (kappa or) modulated apoptosi s was investigated in CNE2 human epithelial tumor cells. Induction of these cells to undergo apoptosis with staurosporine was associated with a massiv e increase in intracellular cAMP level. The inhibition of the increase in c AMP partially inhibited apoptosis as evidenced by a reduction of PARP and c aspase-3 cleavage. Accordingly, a low but significant level of apoptosis is induced in these cells by the elevation of cAMP through the addition of fo rskolin and isobutylmethylxanthine. The existence of a cAMP-dependent and a cAMP-independent apoptotic pathway is therefore suggested. Receptor bindin g studies, RT-PCR experiments and Western blot analysis demonstrated the pr esence of type 1 kappa or in the CNE2 cells. Stimulation of kappa or in the se cells resulted in the production of inositol (1,4,5)-trisphosphate, redu ction of cAMP level and a marked enhancement of staurosporine-induced apopt osis. The potentiation of apoptosis by kappa or was prevented by inhibition of phospholipase C but was slightly enhanced by the presence of the active cAMP analogues, 8-CPT-cAMP and dibutyryl-cAMP. These data demonstrate for the first time that the phospholipase C pathway activated by type 1 kappa o r expressed by cancer cells is involved in the potentiation of apoptosis. ( C) 2000 Elsevier Science B.V. All rights reserved.