concanamycin-a and Melanoma

In tyrosinase-positive amelanotic melanoma cells, inactive tyrosinase accumulates in the endoplasmic reticulum. Based on studies described here, we propose that aberrant vacuolar proton ATPase (V-ATPase)-mediated proton transport in melanoma cells disrupts tyrosinase trafficking through the secretory pathway. Amelanotic but not melanotic melanoma cells or normal melanocytes display elevated proton export as observed by the acidification of the extracellular medium and their ability to maintain neutral intracellular pH. Tyrosinase activity and transit through the Golgi were restored by either maintaining the melanoma cells in alkaline medium (pH 7.4-7.7) or by restricting glucose uptake. The translocation of tyrosinase out of the endoplasmic reticulum and the induction of cell pigmentation in the presence of the ionophore monensin or the specific V-ATPase inhibitors concanamycin A and bafilomycin A1 supported a role for V-ATPases in this process. Because it was previously shown that V-ATPase activity is increased in solid tumors in response to an acidified environment, the appearance of hypopigmented cells in tyrosinase-positive melanoma tumors may indicate the onset of enhanced glycolysis and extracellular acidification, conditions known to favor metastatic spread and resistance to weak base chemotherapeutic drugs.

Topics: Acids; Anti-Bacterial Agents; Cells, Cultured; Endoplasmic Reticulum; Enzyme Inhibitors; Glucose; Golgi Apparatus; Humans; Hydrogen-Ion Concentration; Macrolides; Melanoma; Monophenol Monooxygenase; Tumor Cells, Cultured; Vacuolar Proton-Translocating ATPases

In this study, we describe the activation of melanogenesis by selective vacuolar type H(+)-ATPase inhibitors (bafilomycin A1 and concanamycin A) in amelanotic human and mouse melanoma cells which express tyrosinase but show no melanogenesis. Addition of the inhibitors activated tyrosinase within 4 h, and by 24 h the cells contained measurable amounts of melanin. These effects were not inhibited by cycloheximide (2 microgram/ml) which is consistent with a post-translational mechanism of activation. Our findings suggest that melanosomal pH could be an important and dynamic factor in the control of melanogenesis in mammalian cells.

Topics: Animals; Anti-Bacterial Agents; Cycloheximide; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Humans; Hydrogen-Ion Concentration; Macrolides; Melanins; Melanoma; Melanosomes; Mice; Monophenol Monooxygenase; Protein Processing, Post-Translational; Proton-Translocating ATPases; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors; Tumor Cells, Cultured; Vacuolar Proton-Translocating ATPases