RESUMEN
BACKGROUND: In the last decade, Hermansky-Pudlak syndrome (HPS) has arisen as an instructive disorder for cell biologists to study the biogenesis of lysosome related organelles (LROs). Of the eight human HPS subtypes, only subtypes 1 through 5 are well described. AIM: To characterise extensively the HPS-6 subtype, caused by defects in HPS6, a subunit of the biogenesis of lysosome related organelles complex-2 (BLOC-2). METHODS: Mutation analysis for the HPS6 gene was performed on DNA from our group of unclassified HPS patients. The clinical phenotype of patients with HPS6 mutations was then carefully ascertained, and their cultured dermal melanocytes were employed for cellular immunofluorescence studies. RESULTS: Molecular studies showed a variety of mutations in the single exon HPS6 gene, including frame shift, missense, and nonsense mutations as well as a approximately 20 kb deletion spanning the entire HPS6 genomic region. Cellular studies revealed that the melanogenic proteins tyrosinase and tyrosinase related protein 1 failed to be efficiently delivered to the melanosomes of HPS-6 patients, explaining their hypopigmentation. Clinical studies indicated that HPS-6 patients exhibit oculocutaneous albinism and a bleeding diathesis. Importantly, granulomatous colitis and pulmonary fibrosis, debilitating features present in HPS subtypes 1 and 4, were not detected in our HPS-6 patients. CONCLUSION: The HPS-6 subtype resembles other BLOC-2 defective subtypes (that is, HPS-3 and HPS-5) in its molecular, cellular and clinical findings. These findings are not only important for providing a prognosis to newly diagnosed HPS-6 patients, but also for further elucidation of HPS function in the biogenesis of LROs.
Asunto(s)
Síndrome de Hermanski-Pudlak/genética , Síndrome de Hermanski-Pudlak/patología , Péptidos y Proteínas de Señalización Intracelular/genética , Adolescente , Adulto , Secuencia de Aminoácidos , Secuencia de Bases , Northern Blotting , ADN/química , ADN/genética , Femenino , Variación Genética , Humanos , Inmunohistoquímica , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Masculino , Melanosomas/genética , Melanosomas/patología , Persona de Mediana Edad , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa , Polimorfismo de Nucleótido Simple , Adulto JovenRESUMEN
One essential part of the process of skin pigmentation comprises the production of melanosomes, the melanin-containing organelles, and correct transport towards their target cells, the keratinocytes. In this overview the molecular mechanisms of these processes are discussed in view of a number of pigmentation syndromes.
Asunto(s)
Proteínas Portadoras/fisiología , Melanosomas/fisiología , Trastornos de la Pigmentación/genética , Pigmentación de la Piel/fisiología , Transporte Biológico Activo , Humanos , Queratinocitos/metabolismo , Melanocitos , Pigmentación de la Piel/genéticaRESUMEN
In this review an overview of recent advances in the understanding of melanosome movement within epidermal melanocytes is given. Exploration of the molecular events involved in and determining the process of melanosome transport, as an essential part of human pigmentation, could lead to the identification of agents that augment, or down-regulate the transfer of melanosomes to surrounding keratinocytes. This would present a major breakthrough in the possibilities to influence pigmentation and related disorders, of great concern to some patients. Moreover, melanosome transport offers a good model to study mammalian organelle trafficking and its key players in general.
Asunto(s)
Transporte Biológico/fisiología , Síndromes de Inmunodeficiencia/genética , Melanosomas/metabolismo , Proteínas Motoras Moleculares/metabolismo , Cadenas Pesadas de Miosina/genética , Miosina Tipo V/genética , Trastornos de la Pigmentación/genética , Empalme Alternativo , Animales , Dineínas/metabolismo , Células Epidérmicas , Epidermis/metabolismo , Humanos , Cinesinas/metabolismo , Melaninas/metabolismo , Melanocitos/citología , Melanocitos/metabolismo , Modelos Biológicos , Cadenas Pesadas de Miosina/metabolismo , Miosina Tipo V/metabolismo , Síndrome , Proteínas de Unión al GTP rab/genética , Proteínas de Unión al GTP rab/metabolismo , Proteínas rab27 de Unión a GTPRESUMEN
Melanocytic dendrites consist of a central core of microtubules (MT) and a subcortical actin network. In previous reports we showed the presence of MT-associated motor proteins kinesin and cytoplasmic dynein on the melanosomal surface, forming a link with MT (Vancoillie et al. J Invest Dermatol 2000;114:421-429; Vancoillie et al. Br J Dermatol 2000;143:258-306). We could also demonstrate the association of kinectin, the kinesin receptor, with melanosomes. The interaction of cytoplasmic dynein with its cargoes is thought to be indirectly mediated by dynactin, a complex that binds to the dynein intermediate chain. Therefore, in this study, we investigated the in vitro expression of dynactin subunits P150Glued and P50 in normal human epidermal melanocytes, keratinocytes, and dermal fibroblasts by reverse transcription-polymerase chain reaction and northern blot analysis. In an attempt to gain an insight into the subcellular localization of dynactin, immunofluorescence and immunoelectron microscopy (IEM) studies were performed. The two isoforms of P150Glued and P50 are expressed in all studied skin cells. Immunofluorescence staining shows punctate distributions for P150Glued and P50 in melanocytes. P150Glued shows a clear centrosomal staining and accentuation in the dendrite tips. P50 is also accentuated in the perinuclear area and dendrite tips. Immunofluorescence double-labeling with a melanosome marker showed apparent colocalization of both P150Glued and P50 with melanosomes. By IEM, P50 is detected on the surface of the majority of melanosomes in melanocytes. The colocalization of different subunits of the dynactin complex with melanosomes is consistent with the earlier finding of cytoplasmic dynein association with melanosomes and supports the hypothesis that this complex could form a link between cytoplasmic dynein and the melanosomal membrane.