Induction of autocrine factor inhibiting cell motility from murine B16-BL6melanoma cells by alpha-melanocyte stimulating hormone

We have previously reported that neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) successfully inhibited Matrigel invasion and haptotacti c migration of B16-BL6 melanoma cells towards both fibronectin and laminin without affecting their growth. In the present study, we investigated the i nhibitory mechanism of tumor cell motility by alpha-MSH, alpha-MSH signific antly blocked the autocrine motility factor (AMF)-enhanced cell motility, H owever, alpha-MSH did neither prevent the secretion of AMF from B16-BL6 cel ls nor alter the expression level of AMF receptor (gp78). On the other hand , alpha-MSH induced the secretion of the motility inhibitory factor(s) from B16-BL6 cells in a concentration- and time-dependent manner. The induction of the motility inhibitor(s) was proportional to increasing levels of intr acellular cAMP induced by alpha-MSH as well as forskolin, and the activity was abolished by an adenylate cyclase inhibitor, 2', 5'-dideoxyadenosine (D DA). The motility-inhibiting activity in conditioned medium (CM) from alpha -MSH-treated B16-BL6 cells was found to have a m.w. below 3 kDa after fract ionation, This activity was abolished by boiling but insensitive to trypsin , The treatment of tumor cells with cycloheximide reduced the activity in a lpha-MSH-stimulated CM. Our results suggest that alpha-MSH inhibited the mo tility of B16-BL6 cells through induction of autocrine factor(s). Int. J. C ancer, 80:889-895, 1999. (C) 1999 Wiley-Liss, Inc.