The absence of Rab27a accelerates the degradation of Melanophilin

Abstract

Melanophilin (Mlph) forms an interaction with Rab27a and the actin‐based motor protein MyosinVa (MyoVa) on mature melanosome membranes and the tripartite complex regulates melanosome transport in melanocytes. In this study, we found that Rab27a siRNA decreased Mlph and Rab27a protein levels, but Mlph mRNA levels were not changed. Other Rab27a siRNA sequences also showed the same results. When Rab27a siRNA was treated with melan‐a melanocytes, Rab27a protein was decreased within 6 hours and Mlph protein was decreased within 24 hours. To determine whether the absence of Rab27a promotes Mlph degradation, we inhibited protein degradation by treatment with proteasome (MG132) and lysosomal enzyme (E64D and Pepstatin A) inhibitors in melan‐a melanocytes. MG132 inhibited the degradation of Mlph, but E64D and Pepstatin A had no effect on Mlph. The absence of Rab27a enhanced ubiquitination of Mlph and induced proteasomal degradation. From these results, we concluded that Mlph interaction with Rab27a is important for Mlph stability and melanosome transport.

Rab GTPases: Key players in melanosome biogenesis, transport, and transfer

“…Under physiological conditions, however, it is unclear whether EPI64/TBC1D10A is required for cargo (i.e., melanosome) unloading after actin‐dependent melanosome transport mediated by the Rab27A–Mlph/Slac2‐a–myosin Va tripartite complex. Since Mlph/Slac2‐a contains multiple PEST sequences that are highly sensitive to proteases and it undergoes proteasome‐mediated degradation, degradation of Mlph/Slac2‐a may result in disassembly of the tripartite protein complex and cargo unloading (Fukuda & Itoh, 2004; Park et al., 2019).…”

Slac2-b Coordinates Extracellular Vesicle Secretion to Regulate Keratinocyte Adhesion and Migration

“…A similar phenotype was observed in a recent study, where the knockdown of KIBRA, an adaptor protein for Rab27a, lead to the reduction in Rab27a protein expression (Song et al, 2019), as KIBRA interacts with Rab27a, stabilizing the protein and preventing its degradation via the ubiquitin-proteasome pathway. Another study demonstrated that Rab27a knockdown in melanocytes led to reduced levels of the effector protein Melanophilin due to an increase in proteasomal degradation (Park et al, 2019). This has also been in shown in vivo using Rab27a-deficient mice (Wu et al, 2002), suggesting that the interactions between Rab27 isoforms and their effectors are essential to the stability of each other.…”

Investigating the impact of pigmentation variation of breast muscle on growth traits, melanin deposition, and gene expression in Xuefeng black-bone chickens

“…It may play a significant role in both intestine and inner ear biology ( Choi et al, 2020 ; Kapustina and Cheney, 2020 ). We speculated that CALML4 maybe need combined with other melanin-related proteins to form a complex that participates in melanin production, similar to how melanophilin requires binding with Rab27a and myosin Va to affect melanosomes transport ( Park et al, 2019 ). And we found 2 potential candidate genes ( KITLG and EDNRB ) in female chicken, which could help us exhaustive understand the mechanisms of melanin production.…”