Molecular mechanism of melanin transfer from donor melanocytes to recipient keratinocytes
Year: 2015
Type: dissertation
Abstract: The skin is the largest organ of the human body. From ancient times, the color of skin has been an intriguing feature. Moreover, a large number of diseases are associated with skin disorders such as Griscelli syndrome, Hermansky-Pudlak syndrome and Waardenburg syndrome. Therefore, therapies directed to pigmentation disorders and also cosmetic applications have been intensively studied. Thus it is essential to understand the molecular mechanisms underlying of pigmentation disorders. The “epidermal-melanin unit” is the functional complex that confers color and photoprotective properties to the skin. This unit is composed by melanocytes and keratinocytes. Epidermal melanocytes are highly specialized cells that synthesize and store the pigment melanin in unique membrane-bound organelles termed melanosomes. Once mature, melanosomes are transferred to neighbor keratinocytes and transported to the apical area of the cell where they form the protective melanin cap. Skin pigmentation results from three sequential processes: (i) the biogenesis of melanin in melanocytes; (ii) the transport from its site of synthesis in the perinuclear area of the cell to the periphery; and finally, (iii) the transfer to receptor keratinocytes. In this work, we focused on the transfer of melanin. Previous studies from our group support the model of coupled exo-endocytosis of melanin transfer from melanocytes to keratinocytes. As Rab GTPases are master regulators of intracellular trafficking and have already been implicated in several steps of skin pigmentation (melanogenesis and transfer of melanin), the group proposed to continue investigating the molecular mechanisms of the melanin transfer and found that Rab11b mediates the exocytosis and transfer of melanin from melanocytes to keratinocytes. The aim of this work is to identify Rab11b effectors, which bind to the active form of small GTPases, in melanocytes. Since Rab11-family interacting proteins (Rab11-FIPs) are described to be effectors of Rab11, we studied if they could have a role in the secretion of melanin from melanocytes. Moreover, this analysis was done downregulating each protein and observing if there was a decrease in melanin exocytosis. We found that FIP2 as well as Myosin Va can play a role in this process, since the silencing of each of these proteins impaired melanin secretion by melanocytes. Furthermore, we analyzed the localization of each FIP as well as Myosin Va in melanocytes by overexpressed tagged forms of these proteins. We also analyzed a possible association between these proteins and melanosomes. Relatively to FIP2, we found that this protein co-localize with Rab11b, when both overexpressed, in close proximity with melanosomes along of cytoplasmic membrane. Myosin Va also co-localize with Rab11b but in dendrite tips of melanocytes. At this point, the disposition of FIP3 also gave us good evidences to play a role in melanin secretion. FIP3 co-localize with Rab11b, when both proteins overexpressed, in microtubule-organizing center, changing the normal localization of Rab11b in the cell. Melanosomes also change its disposition, becoming dispersed in all cytoplasmic region. In summary, our studies indicate that FIP2, FIP3 and Myosin Va are required for the secretion of melanin by melanocytes.
Author: Tiago André Carrilho Festas
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2201265998