The ocular albinism type 1 (OA1) G-protein-coupled receptor functions with MART-1 at early stages of melanogenesis to control melanosome identity and composition

Hum Mol Genet. 2009 Dec 1;18(23):4530-45. doi: 10.1093/hmg/ddp415. Epub 2009 Aug 28.

Abstract

OA1 (GPR143; GPCR, G-protein-coupled receptor), the protein product of the ocular albinism type 1 gene, encodes a pigment-cell-specific GPCR that localizes intracellularly to melanosomes. OA1 mutations result in ocular albinism due to alterations in melanosome formation, suggesting that OA1 is a key player in the biogenesis of melanosomes. To address the function of OA1 in melanosome biogenesis, we have used siRNA inactivation and combined morphological and biochemical methods to investigate melanosome ultrastructure, melanosomal protein localization and expression in human pigmented melanocytic cells. OA1 loss of function leads to decreased pigmentation and causes formation of enlarged aberrant premelanosomes harboring disorganized fibrillar structures and displaying proteins of mature melanosomes and lysosomes at their membrane. Moreover, we show that OA1 interacts biochemically with the premelanosomal protein MART-1. Inactivation of MART-1 by siRNA leads to a decreased stability of OA1 and is accompanied by similar defects in premelanosome biogenesis and composition. These data show for the first time that melanosome composition and identity are regulated at early stages by OA1 and that MART-1 likely acts as an escort protein for this GPCR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Neoplasm / genetics
  • Antigens, Neoplasm / metabolism*
  • Cell Line, Tumor
  • Cells, Cultured
  • Eye Proteins / genetics
  • Eye Proteins / metabolism*
  • Humans
  • MART-1 Antigen
  • Melanocytes / metabolism*
  • Melanosomes / genetics
  • Melanosomes / metabolism*
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Mice, Knockout
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism*
  • Protein Binding
  • Protein Transport
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Retina / growth & development*
  • Retina / metabolism

Substances

  • Antigens, Neoplasm
  • Eye Proteins
  • GPR143 protein, human
  • Gpr143 protein, mouse
  • MART-1 Antigen
  • MLANA protein, human
  • Membrane Glycoproteins
  • Mlana protein, mouse
  • Neoplasm Proteins
  • Receptors, G-Protein-Coupled