Hermansky-Pudlak syndrome: vesicle formation from yeast to man

The disorders known as Hermansky-Pudlak syndrome (HPS) are a group of genetic diseases resulting from abnormal formation of intracellular vesicles. In HPS, dysfunction of melanosomes results in oculocutaneous albinism, and absence of platelet dense bodies causes a bleeding diathesis. In addition, some HPS patients suffer granulomatous colitis or fatal pulmonary fibrosis, perhaps due to mistrafficking of a subset of lysosomes. The impaired function of specific organelles indicates that the causative genes encode proteins operative in the formation of certain vesicles. Four such genes, HPS1, ADTB3A, HPS3, and HPS4, are associated with the four known subtypes of HPS, i.e. HPS-1, HPS-2, HPS-3, and HPS-4. ADTB3A codes for the beta 3 A subunit of adaptor complex-3, known to assist in vesicle formation from the trans-Golgi network or late endosome. However, the functions of the HPS1, HPS3, and HPS4 gene products remain unknown. These three genes arose with the evolution of mammals and have no homologs in yeast, reflecting their specialized function. In contrast, all four known HPS-causing genes have homologs in mice, a species with 14 different models of HPS, i.e. hypopigmentation and a platelet storage pool deficiency. Pursuit of the mechanism of mammalian vesicle formation and trafficking, impaired in HPS, relies upon investigation of these mouse models as well as studies of protein complexes involved in yeast vacuole formation.