1. ¹Department of Dermatology, Ghent University Hospital, Ghent, Belgium
2. ²Institut de Recherche Pierre Fabre, Centre de Recherche sur la Peau, Toulouse Cedex, France
3. ³Pierre Fabre SA, Toulouse, France

Correspondence: Mireille Van Gele, Department of Dermatology, Ghent University Hospital, P6, De Pintelaan 185, Ghent 9000, Belgium. E-mail: mireille.vangele@ugent.be

Received 24 October 2007; Revised 14 February 2008; Accepted 22 February 2008; Published online 10 April 2008.

Abstract

The movement of melanosomes, dense melanin-containing organelles, within human melanocytes is actin-dependent and mediated through the formation of a Rab27a-Slac2-a–myosin Va (MyoVa) protein complex. We previously showed that only the melanocyte-specific exon F isoforms of MyoVa are involved in melanosome transport to the dendrite extremities. Here, we investigate siRNA to downregulate the exon F-containing isoforms of MyoVa in primary human melanocytes. Efficient and specific knockdown of the MyoVa exon F isofoms were shown at both mRNA and protein levels. Further, a stable shRNA against the MyoVa exon F isoforms was prepared by using a lentiviral system to improve and confirm the silencing effect in hard-to-transfect melanocyte cells. Immunofluorescence microscopy shows that knockdown of the exon F isoforms results in blockade of intramelanocytic melanosome transport due to the inability to form the Rab27a-Slac2-a–MyoVa tripartite complex. Interestingly, the observed phenotypic effect (that is, perinuclear accumulation of melanosomes) is the same as that seen in melanocytes from patients with human Griscelli syndrome causing abnormal pigmentation. We conclude that our siRNA-based strategy provides a previously unreported tool to block the intracellular melanosome movement in primary human melanocytes and may become an innovative drug to treat hyperpigmentation.