Response of mouse melanoma cells to melanocyte stimulating hormone

Abstract

WE have recently described a mouse melanoma cell line which responds to melanocyte stimulating hormone (MSH) with dramatic increases in tyrosinase activity and melanin content, as well as changes in cellular morphology and growth characteristics^1–3. The increase in pigmentation following exposure to MSH is shown in Fig. 1. Cyclic AMP or dibutyryl cyclic AMP may be substituted for MSH in eliciting these responses; consistent with other work suggesting that MSH acts through cyclic AMP in the control of pigmentation in vertebrates^4–7. In our previous studies we used non-synchronised mouse melanoma cells grown in monolayer culture. Martin et al.⁸ have shown that synchronised mouse HTC cells respond to corticosteroids with increased tyrosine amino transferase synthesis in the late Gl and early S periods of the cell cycle; similarly, Buell and Fahey⁹ have shown, using a synchronised human lymphoid cell line, that immunoglobulins G and M are expressed in late Gl and S. We wished to investigate the effects of MSH on tyrosinase activity and endogenous cyclic AMP levels in synchronised cells to determine if there is a particular hormone-sensitive phase of the melanoma cell cycle. We report here that melanoma cells responded maximally to MSH with increased tyrosinase activity and cyclic AMP content during the G2 phase.