Regulation of cell division and of tyrosinase in B16 melanoma cells by imidazole: A possible role for the concept of metabolite Gene regulation in mammalian cells

Abstract

Results of hemacytometer cell counts and of tyrosinase measurements made by the Pomerantz method demonstrate that imidazole added to the medium of cultured B16 mouse melanoma cells can stimulate tyrosinase specific activity and inhibit cell division. These effects are greater than with adenosine 3',5' cyclic monophosphate (cAMP) or the cAMP-phosphodiesterase inhibitor theophylline. The effects of imidazole on cell division and tyrosinase are enhanced by theophylline and antagonized by cAMP. Cyclic AMP-phosphodiesterase activity in cell-free extracts can be inhibited by theophylline and stimulated by imidazole. However, imidazole does not affect cAMP-phosphodiesterase specific activity in vivo, nor does it affect intracellular cAMP concentrations as determined by competitive protein-binding assays. In contrast, the specific activity of cAMP-phosphodiesterase in vivo is stimulated by cAMP and theophylline, supporting the hypothesis that cAMP and agents which increase intracellular cAMP concentrations induce the synthesis of cAMP-phosphodiesterase. Studies with actinomycin-D and cycloheximide support the hypothesis that cAMP can also mediate posttranslational activation of tyrosinase. Similar experiments suggest that imidazole, or a derivative thereof, can induce the synthesis of tyrosinase at the pretranslational level of control. We hypothesize that this type of regulation (pretranslational) by imidazole may define a role for the concept of "Metabolite Gene Regulation" (MGR), in mammalian cells.

Stimulation of tyrosinase activity of cultured melanoma cells by lysosomotropic agents

“…Results with imidazole confirmed those reported by Montefiori and Kline (1981). The increase in TyH seems due to de novo synthesis of tyrosinase, because it was inhibited by cycloheximide at neutral pH (Table 2), where the degradation of tyrosinase is not inhibited by ammonium chloride (Saeki and Oikawa, 1980).…”

Inhibition of imidazole‐induced tyrosinase activity by estradiol and estriol in cultured B 16/C3 melanoma cells

“…While the imidazole effect in B16 melanogenesis appears pre-translational on the basis of inhibitor studies (Montefiori and Kline, 1981), whether transcription of the tyrosinase structural gene is itself being regulated is not yet known.…”

“…B16/C3 mouse melanoma cell cultures were incubated at 37°C in 25-cm2 plastic flasks (Corning Medical, Med- (Montefiori and Kline, 1981). Cells were removed for passage in calcium-free, magnesiumfree phosphate buffered saline containing 0.05% EDTA disodium, pH 7.4 (0.05% EDTA disodium in CMF-PBS).…”

Active melanogenesis in non-S phase melanocytes in B16 melanomas in vivo investigated by double-tracer microautoradiography with 18F-fluorodopa and 3H-thymidine

“…In cultured melanin-producing cells, melanogenesis has been reported to be a function of the growth phase of the cells (Oikawa et al, 1972;Steinberg & Whittaker, 1976;Montefiori & Kline, 1981;Bennett, 1989), as well as of extracellular pH and ionic strength (Saeki & Oikawa, 1978; Laskin et al, There were no significant differences in the cells among the three cell lines, except for 3H-unlabelled melanocytes (aP<0.05).…”