The Hermansky-Pudlak Syndrome (HPS) is a congenital, potentially fatal, multi-system disorder presenting with oculocutaneous albinism, a mild to severe bleeding diathesis, and ceroid storage disease. These characteristics result from aberrations in a specific group of cellular organelles, (i.e., the pigment granule of the melanocyte, the dense bodies of the platelet, and the lysosome/residual body of the reticular cell respectively). HPS is an autosomal recessive disease that is somewhat prevalent in the United States and relatively frequent in Puerto Rico (1:1800 affected). The single gene affected in HPS putatively regulates a common feature in the biosynthesis and/or maintenance of the three types of specific cellular organelles involved. In common, these organelles either originate and/or receive specific glycoproteins from the Golgi apparatus. Thus it is hypothesized that the HPS gene product regulates selective trafficking from the trans Golgi network to distinct target organelles. The gene for HPS has recently been cloned. The deduced amino acid sequence it encodes has no significant homologies with any known protein. Therefore, this molecule appears to be a unique protein. The HPS gene product does contain motifs suggestive of a signal sequence, transmembrane domains, glycosylation sites, cysteine rich areas, and several lysosome/endosome trafficking motifs. Thus it is hypothesized to be a glycoprotein synthesized at the RER and trafficked to the limiting membranes of the specific organelles discussed. We propose to confirm the ultimate site of localization of the HPS gene product and its mode of synthesis using the melanocyte system. In addition, we will investigate its role in melanization and identify a candidate binding partner it must use for the fusion/docking process in its selective trafficking function. Specifically, cultured human melanocytes will be assessed for the immunocytochemical localization and biosynthesis analysis of the HPS gene product using a panel of antibodies generated against the HPS gene product. In addition, melanoma cells transfected with the anti-sense HPS cDNA and melanocytes cultured from patients with HPS will be used as artificial and natural knock-out models respectively to analyze the concurrent alteration in trafficking of various melanocyte specific gene products. In addition, HPS melanocytes will be transfected with the sense HPS cDNA in an attempt to correct the morphological/translocation defect. Finally, immunoprecipitation/immunoblotting experiments along with the Yeast Two-Hybrid system will be utilized to identify proteins that bind to the HPS gene product as candidate molecules that co-operate in the targeting process. These studies will contribute to our knowledge of cellular trafficking in general and the pathophysiology of HPS in specific.
