Rab8 Regulates the Actin-based Movement of Melanosomes

Abstract

Rab GTPases have been implicated in the regulation of specific microtubule-and actin-based motor proteins. We devised an in vitro motility assay reconstituting the movement of melanosomes on actin bundles in the presence of ATP to investigate the role of Rab proteins in the actin-dependent movement of melanosomes. Using this assay, we confirmed that Rab27 is required for the actin-dependent movement of melanosomes, and we showed that a second Rab protein, Rab8, also regulates this movement. Rab8 was partially associated with mature melanosomes. Expression of Rab8Q67L perturbed the cellular distribution and increased the frequency of microtubule-independent movement of melanosomes in vivo. Furthermore, anti-Rab8 antibodies decreased the number of melanosomes moving in vitro on actin bundles, whereas melanosomes isolated from cells expressing Rab8Q67L exhibited 70% more movements than wild-type melanosomes. Together, our observations suggest that Rab8 is involved in regulating the actin-dependent movement of melanosomes.

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

“…The lack of interaction of Myosin Vc with Rab11 or Rab17 suggests the function ascribed to these Rabs in melanosome secretion is independent of Myosin Vc. Another pair of relevant Rabs is that of Rab7a and Rab8a, which in melanocytes localize to immature and mature melanosomes, respectively (66,67). In this context the interaction between these Rabs and Myosin Vc (Fig.…”

“…In melanocytes, Rab7a localizes to immature stage I-III melanosomes and Rab8a to more mature, pigmented melanosomes and may be involved in melanosome biogenesis (66,67). Therefore, we tested for interaction between the constitutively active, GTP-locked mutant version of these Rabs and Myosin Vc as well as Myosin Va and Myosin Vb (Fig.…”

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…Microtubule dependent bidirectional movement of melanosomes requires a functional MEK-ERK complex on melanosomes bound by an unknown scaffold molecule [175,176]. The small GTPases, Rab7, Rab8 and Rab27, through their interaction with motors, have been implicated in melanosome movement [177][178][179][180][181][182] and a few Rabs are targets for ERK phosphorylation [183], raising the possibility that ERK signaling may influence Rab functions necessary for melanosome traffic. ERK dependent traffic of melanosomes is regulated by minus end directed dynein motors, that raised the speculation that ERK may directly regulate dynein activity [184] and thereby influence intracellular mobility of signaling complexes and organelles.…”

A C2 domain protein kinase initiates phagocytosis in the protozoan parasite Entamoeba histolytica

“…Therefore, phagocytosis in E. histolytica is likely to follow a different molecular path. Some of the molecules that have been identified are components of the cytoskeleton 17 and its regulators [18][19][20][21][22][23][24][25] including phosphoinositides and one of the FYVE-domain-containing protein EhFP4 26 . Analysis of the phagosome proteome has revealed involvement of a large number of proteins in phagosome formation and subsequent maturation 27,28 .…”