da Silva Bizario João Carlos, da Cunha Nascimento Alexandra Aparecida, Casaletti Luciana, Patussi Eliana Valéria, Chociay Maria Fernanda, Larson Roy Edward, Espreafico Enilza Maria
Department of Molecular and Cellular Biology and Pathogenic Bioagents, Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, Brazil.
Cell Motil Cytoskeleton. 2002 Feb;51(2):57-75. doi: 10.1002/cm.10010.
Myosin-Va has been implicated in melanosome translocation, but the exact molecular mechanisms underlying this function are not known. In the dilute, S91 melanoma cells, melanosomes move to the cell periphery but do not accumulate in the tips of dendrites as occurs in wild-type B16 melanocytes; rather, they return and accumulate primarily at the pericentrosomal region in a microtubule-dependent manner. Expression of the full-length neuronal isoform of myosin-Va in S91 cells causes melanosomes to disperse, occupying a cellular area approximately twice that observed in non-transfected cells, suggesting a partial rescue of the dilute phenotype. Overexpression of the full tail domain in S91 cells is not sufficient to induce melanosome dispersion, rather it causes melanosomal clumping. Overexpression of the head and head-neck domains of myosin-Va in B16 cells does not alter the melanosome distribution. However, overexpression of the full tail domain in these cells induces melanosome aggregation and the appearance of tail-associated, aggregated particles or vesicular structures that exhibit variable degrees of staining for melanosomal and Golgi beta-COP markers, as well as colocalization with the endogenous myosin-Va. Altogether, the present data suggest that myosin-Va plays a role in regulating the direction of microtubule-dependent melanosome translocation, in addition to promoting the capture of melanosomes at the cell periphery as suggested by previous studies. These studies also reinforce the notion that myosin-V has a broader function in melanocytes by acting on vesicular targeting or intracellular protein trafficking.
肌球蛋白-Va与黑素小体转运有关，但其发挥该功能的具体分子机制尚不清楚。在稀释型S91黑色素瘤细胞中，黑素小体向细胞周边移动，但不像野生型B16黑素细胞那样在树突尖端积累；相反，它们返回并主要以微管依赖的方式在中心体周围区域积累。在S91细胞中表达全长神经元型肌球蛋白-Va会导致黑素小体分散，占据的细胞面积约为未转染细胞的两倍，这表明稀释型表型得到了部分挽救。在S91细胞中过表达完整的尾部结构域不足以诱导黑素小体分散，反而会导致黑素小体聚集。在B16细胞中过表达肌球蛋白-Va的头部和头颈结构域不会改变黑素小体的分布。然而，在这些细胞中过表达完整的尾部结构域会诱导黑素小体聚集，并出现与尾部相关的聚集颗粒或囊泡结构，这些结构对黑素小体和高尔基体β-COP标记物呈现不同程度的染色，并且与内源性肌球蛋白-Va共定位。总之，目前的数据表明，肌球蛋白-Va除了如先前研究所表明的促进黑素小体在细胞周边的捕获外，还在调节微管依赖的黑素小体转运方向中发挥作用。这些研究还强化了这样一种观点，即肌球蛋白-V通过作用于囊泡靶向或细胞内蛋白质运输在黑素细胞中具有更广泛的功能。
