Abstract
Some tyrosinase-negative variants which lost detectable tyrosinase activity were isolated from cultured tyrosinase-positive B16 mouse melanoma cells. These were compared with the tyrosinase-positive cell lines with regard to their ability to differentiate and their transformed phenotypes.
None of the tyrosinase-negative variants isolated possessed melanosomes. Attempts to find a tyrosinase inhibitor in the sodium desoxycholate cell lysate of these tyrosinase-negative variants and to induce tyrosinase activity by theophylline treatment were unsuccessful. The tyrosinase-negative variants were exclusively flat and like fibroblasts, whereas the tyrosinase-positive cell lines were rounded and spindle-shaped. Moreover, the tyrosinase-negative variants showed less ability to form colonies in soft agar and greater adhesive-ness to the substratum as compared to the tyrosinase-positive cell lines.
Our results indicate a positive correlation between melanogenic ability and the expression of transformed phenotypes in the constitutively tyrosinase-positive and tyrosinase-negative melanoma cell lines.
