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. 2005 Feb;124(2):420-7.
doi: 10.1111/j.0022-202X.2004.23585.x.

Melanocytes derived from patients with Hermansky-Pudlak Syndrome types 1, 2, and 3 have distinct defects in cargo trafficking

Bonnie Richmond  1 , Marjan Huizing, Jill Knapp, Amy Koshoffer, Yang Zhao, William A Gahl, Raymond E Boissy
Affiliations

Melanocytes derived from patients with Hermansky-Pudlak Syndrome types 1, 2, and 3 have distinct defects in cargo trafficking

Bonnie Richmond et al. J Invest Dermatol. 2005 Feb.

Abstract

Hermansky-Pudlak Syndrome (HPS) is a genetically heterogeneous disorder in which mutations in one of several genes interrupts biogenesis of melanosomes, platelet dense bodies, and lysosomes. Affected patients have oculocutaneous albinism, a bleeding diathesis, and sometimes develop granulomatous colitis or pulmonary fibrosis. In order to assess the role of HPS genes in melanosome biogenesis, melanocytes cultured from patients with HPS subtypes 1, 2, or 3 were assessed for the localization of various melanocyte proteins. Tyrosinase, Tyrp1, and Dct/Tyrp2 were atypically and distinctly expressed in HPS-1 and HPS-3 melanocytes, whereas only tyrosinase showed an atypical distribution in HPS-2 melanocytes. The HPS1 and AP3B1 (i.e., HPS-2) gene products showed no expression in HPS-1 and HPS-2 melanocytes, respectively, whereas HPS-3 melanocytes exhibited normal expression for both proteins. In normal human melanocytes, the HPS1 protein was expressed as an approximately 80 kDa molecule with both granular and reticular intracellular profiles. In HPS-1, lysosome associated membrane protein 1 (LAMP1), and LAMP3 were localized to abnormal large granules; in HPS-2, all LAMPs exhibited a normal granular expression; and in HPS-3, LAMP1, and LAMP3 exhibited a distinct less granular and more floccular pattern. In contrast, the expressions of Rab 27, transferrin, and cKit were unaffected in all three HPS genotypes. These data demonstrate that the three initially identified subtypes of human HPS exhibit distinct defects in the trafficking of various melanocyte-specific proteins.

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Figures

Figure 1
Figure 1. Melanocytes cultured from patients with Hermansky–Pudlak Syndrome (HPS)-1, HPS-2, and HPS-3 exhibit specific alterations in the distribution of tyrosinase gene family members
Cultures of melanocytes derived from an unaffected individual (normal human melanocytes (NHM)) and from patients with HPS-1, HPS-2, or HPS-3 were immunostained for tyrosinase, tyrosinase-related protein-1 (Tyrp1), or DOPAchrome tautomerase/tyrosinase-related protein-2 (Dct/Tyrp2). The NHM exhibited a granular staining pattern with prominent perinuclear localization for all three proteins. HPS-1 melanocytes exhibited a similar granular staining pattern with additional large aggregates (arrows) for all three proteins throughout the melanocytes. HPS-2 melanocytes exhibited a relative restriction of tyrosinase to the cell body with limited or no expression in the dendrites (arrowheads); Tyrp1 and Dct/Tyrp2 exhibited normal expression patterns. HPS-3 melanocytes displayed a floccular staining pattern within the cell body and dendrites for tyrosinase, Tyrp1, and Dct/Tyrp2 expression. Scale bar =10 μm.
Figure 2
Figure 2. Hermansky–Pudlak Syndrome (HPS)-1 melanocytes exhibit a variation in co-localization of tyrosinase and tyrosinase-related protein-1 (Tyrp1) within characteristic large granules/membranous complexes
In HPS-1 melanocytes, the characteristic large granules (arrows) are positive for tyrosinase [red in (a)] and Tyrp1 [green in (b)]. The merged image (c) demonstrates that some large granules contained tyrosinase only (arrow), some show equal co-localization of tyrosinase and Tyrp1 (inset #1), some display prominent co-localization of tyrosinase and Tyrp1 with areas containing tyrosinase only (arrowhead, inset #2), and some show polar expression of tyrosinase (arrowhead, inset #3) and Tyrp1 (half-arrow) with an intervening area of co-localization. Electron microscopic evaluation of HPS-1 melanocytes treated for DOPA histochemistry (d) demonstrates that, within a membranous complex, some cisternae and melanosomes express (arrowheads) or lack (arrows) reaction product, indicating the presence and absence of tyrosinase, respectively. Scale bars =10 (b) and 1.5 (d) μm.
Figure 3
Figure 3. Melanocytes cultured from patients with Hermansky–Pudlak Syndrome (HPS)-1, HPS-2, and HPS-3 exhibit specific alterations in the distribution of HPS gene products
Cultures of melanocytes derived from an unaffected individual (normal human melanocytes (NHM)) and patients with HPS-1, HPS-2, or HPS-3 were immunostained for HPS1 (HPS-p) and the β3A (beta3A) and μ3A (mu3A) subunits of AP3. Expression of HPS1 protein (HPS1p) was similar in NHM, HPS-2 melanocytes, and HPS-3 melanocytes but markedly diminished in HPS-1 melanocytes. Expressions of both β3A and μ3A were normal in NHM, HPS-1 melanocytes, and HPS-3 melanocytes but markedly diminished in HPS-2 melanocytes. N, nucleus. Scale bar =10 μm.
Figure 4
Figure 4. The Hermansky–Pudlak Syndrome (HPS)1 protein is expressed in normal human melanocytes (NHM) and absent in HPS-1 melanocytes
(a) Lysates of cultured melanocytes derived from an HPS-1 patient with the 16 bp duplication (lane 1), a normal Caucasian (lane 2), and a normal African/American (lane 3) individual were processed for western blot analysis using HPS1 antiserum (upper blot) and actin antibody (lower blot). A band of ~ 80 kDa was present in both controls and absent in the HPS-1 samples. Cultured melanocytes derived from a Caucasian individual (b and d) and an HPS-1 patient with the 16 bp duplication (c) were processed for indirect immunofluorescent cytochemistry using HPS1 antiserum. Immunostaining as observed by routine fluorescent microscopy was present predominantly in the cell body of control melanocytes (b) and absent in the HPS-1 melanocytes (c). As observed by confocal microscopy (d), the staining pattern for the HPS-1 protein in NHM was prominent in the perinuclear area of the cell body (asterisk) with a relative reduction in staining in the Golgi area (G) and the dendrites. The perinuclear staining appeared predominantly granular (arrows) with a reticular staining pattern (arrowheads) apparent among the granular profiles. N, nucleus. Scale bars =20 (c) and 7.5 (d) μm.
Figure 5
Figure 5. Melanocytes cultured from patients with Hermansky–Pudlak Syndrome (HPS)-1, HPS-2 and HPS-3 were evaluated for expression of various proteins
Normal human melanocytes (NHM) and HPS-1, HPS-2, or HPS-3 melanocytes were immunostained for LAMP 1–3, Rab 27, transferrin, and cKit. Expression of LAMP1 and LAMP3 was granular and that of LAMP2 was diffuse throughout the NHM. HPS-1 melanocytes exhibited, in addition to the normal localization for LAMP 1–3, localization to large granules (arrows) for LAMP1 and LAMP3. HPS-2 melanocytes exhibited normal localization for LAMP 1–3. HPS-3 melanocytes exhibited a more floccular distribution pattern for LAMP1 and LAMP3 and a normal distribution of LAMP2. Expression of Rab27, transferrin, and cKit in NHM exhibited a uniform pattern throughout the melanocytes with a distinct centriole localization (arrows), a punctate pattern throughout the melanocytes, and a diffuse pattern throughout the melanocytes, respectively. HPS-1, HPS-2, and HPS-3 melanocytes exhibit a normal staining pattern for Rab27, transferrin, and cKit. Scale bar =20 μm.
Figure 6
Figure 6. Model for involvement of Hermansky–Pudlak Syndrome (HPS1), HPS2, and HPS3 in the trafficking of tyrosinase gene family members from the Golgi to the melanosome
Tyrosinase, tyrosinase-related protein-1 (Tyrp1), and DOPAchrome tautomerase/tyrosinase-related protein-2 (Dct/Tyrp2) are recruited from the Golgi apparatus into clathrin-coated vesicles to be trafficked along cytoskeletal element to Stage II melanosomes in the perinuclear area. Biogenesis of lysosome-related organelles complexes (BLOC)-2, composed in part of HPS3, HPS5, and HPS6, facilitates this early cargo trafficking event. In the absence of HPS3, cargo vesicles are aberrantly trafficked beyond the perinuclear area. Tyrosinase, and possibly Tyrp1 and Dct/Tyrp2, transit through multivesicular body (MVB)/late endosome-like structures on route to melanosomes. Adaptin3 facilitates the recruitment of tyrosinase from the MVB. In the absence of the β3A subunit of AP3, tyrosinase is aberrantly retained in the MVB. Ultimately, vesicles containing tyrosinase, Tyrp-1, and Dct/Tyrp2 recognize, dock, and fuse with Stage II melanosomes. BLOC-3, composed in part of HPS1 and HPS4, facilitates this later cargo trafficking event. In the absence of HPS1, cargo vesicles are aberrantly trafficked to macroautophagosomes.
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