Myosin Vc Interacts with Rab32 and Rab38 Proteins and Works in the Biogenesis and Secretion of Melanosomes

Jarred J Bultema,Judith A Boyle,Parker B Malenke,Faye E Martin,Esteban C Dell'Angelica,Richard E Cheney,Santiago M Di Pietro

doi:10.1074/jbc.m114.578948

Abstract

Class V myosins are actin-based motors with conserved functions in vesicle and organelle trafficking. Herein we report the discovery of a function for Myosin Vc in melanosome biogenesis as an effector of melanosome-associated Rab GTPases. We isolated Myosin Vc in a yeast two-hybrid screening for proteins that interact with Rab38, a Rab protein involved in the biogenesis of melanosomes and other lysosome-related organelles. Rab38 and its close homolog Rab32 bind to Myosin Vc but not to Myosin Va or Myosin Vb. Binding depends on residues in the switch II region of Rab32 and Rab38 and regions of the Myosin Vc coiled-coil tail domain. Myosin Vc also interacts with Rab7a and Rab8a but not with Rab11, Rab17, and Rab27. Although Myosin Vc is not particularly abundant on pigmented melanosomes, its knockdown in MNT-1 melanocytes caused defects in the trafficking of integral membrane proteins to melanosomes with substantially increased surface expression of Tyrp1, nearly complete loss of Tyrp2, and significant Vamp7 mislocalization. Knockdown of Myosin Vc in MNT-1 cells more than doubled the abundance of pigmented melanosomes but did not change the number of unpigmented melanosomes. Together the data demonstrate a novel role for Myosin Vc in melanosome biogenesis and secretion.

Highlights

The biogenesis of melanosomes and other lysosome-related organelles requires a pair of Rab GTPases, Rab32 and Rab38
We isolated Myosin Vc in a yeast two-hybrid screening for proteins that interact with Rab38, a Rab protein involved in the biogenesis of melanosomes and other lysosome-related organelles
Several studies have demonstrated that the biogenesis of lysosome-related organelles (LROs) in general and melanosomes in particular depends on a combination of ubiquitous and cell type-specific trafficking machinery [1, 14, 21,22,23,24,25, 27, 78]

Summary

Background

The biogenesis of melanosomes and other lysosome-related organelles requires a pair of Rab GTPases, Rab and Rab. Tyrp, and other cargo required for melanosome maturation beyond stage II are delivered from early endosomal tubules and buds (1, 10 –13) This traffic is complex and involves at least two routes that depend on adaptor protein-1 (AP-1), AP-3, biogenesis of lysosome-related organelle complex-1 (BLOC-1), BLOC-2, and BLOC-3 (1, 10 –13). Hermansky-Pudlak syndrome is a disorder characterized by hypopigmentation due to defective melanosome biogenesis and additional manifestations caused by deficiencies in other LROs. Importantly, two closely related members of the Rab family, Rab and Rab, interact physically and functionally with AP-1, AP-3, and the BLOCs to mediate transport of cargo from early endosomal domains to maturing melanosomes (24 –26). Myosin Vc deficiency causes accumulation of pigmented melanosomes in melanocytes, but Myosin Vc is not abundant on pigmented melanosomes, suggesting an indirect role in melanosome secretion

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION