Pituitary adenylate cyclase-activating polypeptide inhibits transforming growth factor-beta 1-induced apoptosis in a human pituitary adenoma cell line

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally i solated from hypothalamic tissues based on its ability to stimulate cAMP pr oduction in cultured anterior pituitary cells. Recent studies have suggeste d a functional role for PACAP in the apoptosis of brain cells. However, the role of PACAP in regulating apoptosis in human pituitary adenomas has not previously been examined, Analysis of the cultured human pituitary adenoma cell line HP75, which expresses all three major PACAP receptors, showed tha t both PACAP-38 and PACAP-27 inhibited TGF-beta 1-induced apoptosis. Treatm ent with the PACAP receptor antagonists PACAP 6-38 (PACAP type I receptor a ntagonist) and (p-chloro-D-Phe(6), Leu(17))-VIP (PACAP type II receptor ant agonist) blocked the effects of PACAP-38 on the inhibition of transforming growth factor-beta 1 (TGF-beta 1)-induced apoptosis, confirming the specifi city of the role of PACAP. Treatment with forskolin but not phorbol 12-myri state 13-actetate (PMA) also inhibited TGF-beta 1-induced apoptosis. TGF-be ta 1 treatment was associated with an increase in mitogen-activated protein kinase (MAP kinase) when analyzed by Western blotting, but PACAP inhibitio n of TGF-beta 1-induced apoptosis was not associated with activation of MAP kinase, Immunocytochemical analysis of the cell cycle cyclin-dependent kin ase inhibitor p27 showed that treatment with TGF-beta 1, forskolin, PMA, an d PACAP increased p27 expression in cultured HP75 cells. These results indi cate that PACAP is a highly specific inhibitor of TGF-beta 1-induced apopto sis in the HP75 human pituitary adenoma cell line and that PACAP, TGF-beta 1, forskolin, and PMA all stimulate expression of the TGF-beta-regulated ce ll cycle protein p27 in the HP75 human pituitary adenoma cell, line. The HP 75 cell line can be used as a model to study the regulation of apoptosis:in human pituitary cells.