Oculocutaneous albinism: Developing novel antibodies targeting the proteins associated with OCA2 and OCA4

• Antibodies were generated against the P and MATP proteins in human melanocytes.
• The intracellular colocalization of P and MATP with BLOC-1 was identified.
• BLOC-1 sorting is critical for the trafficking of tyrosinase to melanosomes.
• The results suggest the mechanism of hypopigmentation underlying OCA2 and OCA4.

BackgroundPatients with oculocutaneous albinism (OCA) have severely decreased pigmentation of their skin, hair and eyes. OCA2 and OCA4 result from mutations of the OCA2 and SLC45A2 genes, respectively, both of which disrupt the trafficking of the critical melanogenic enzyme tyrosinase to melanosomes. Both proteins encoded by those loci (termed P and MATP, respectively) have 12 putative transmembrane regions and are thought to function as transporters, although their functions and subcellular localizations remain to be characterized.ObjectiveTo generate specific antibodies against unique synthetic peptides encoded by P and MATP that could be used to characterize their functions and subcellular localizations.MethodsWestern blotting and immunohistochemistry were used to assess the specificity of antibodies and to colocalize P and MATP proteins with various subcellular markers.ResultsSpecific antibodies to the P and MATP proteins were generated that work well for Western blotting and immunohistochemistry. The localizations of P and MATP with various subcellular organelles were characterized using confocal microscopy, which revealed that they colocalize to some extent with LAMP2, but do not significantly colocalize with markers of the ER, Golgi or melanosomes. Interestingly, both P and MATP colocalize significantly with BLOC-1, a sorting component involved in the intracellular trafficking of melanosomal/lysosomal constituents.ConclusionThese results provide a basis to understand how disrupted functions of P or MATP result in the misrouting of tyrosinase and cause the hypopigmentation seen in OCA2 and OCA4.