PACAP(6-38) is a PACAP receptor antagonist for breast cancer cells

The effects of pituitary adenylate cyclase activating polypeptide (PACAP) a nalogs were investigated using breast cancer cells. I-125-PACAP-27 bound wi th high affinity (Kd = 5 nM) to T47D cells (Bmax = 29,000 per cell). Specif ic I-125-PACAP-27 binding was inhibited half maximally by PACAP-27, PACAP-3 8, PACAP(6-38) and PACAP(28-38) with IC50 values of 8, 17, 750 and > 3000 n M, respectively. By RT-PCR, PACAP receptor mRNA was present in MCF-7 and T4 7D cell lines. Polyclonal antibodies to a PACAP receptor fragment (A-8-C) w ere elicited. The antibodies were affinity purified, recognized a 60-kDa pr otein by western blot, and stained malignant cells in breast cancer biopsy specimens by immunohistochemistry. PACAP-27 elevated the cAMP in T47D cells and the increase in cAMP caused by PACAP was inhibited by PACAP(6-38). PAC AP-27 stimulated c-fos mRNA in T47D cells and the increase in c-fos gene ex pression caused by PACAP was reversed by PACAP(6-38). PACAP(6-38) inhibited colony formation using a soft agar assay and inhibited breast cancer xenog raft growth in nude mice. These data suggest that PACAP(6-38) functions as a breast cancer PACAP receptor antagonist.