The Tetraspanin CD63 Regulates ESCRT-Independent and -Dependent Endosomal Sorting during Melanogenesis

Institut Curie, Centre de Recherche, F-75248 Paris, France.
Developmental Cell (Impact Factor: 9.71). 09/2011; 21(4):708-21. DOI: 10.1016/j.devcel.2011.08.019
Source: PubMed


Cargo sorting to intraluminal vesicles (ILVs) of multivesicular endosomes is required for lysosome-related organelle (LRO) biogenesis. PMEL-a component of melanocyte LROs (melanosomes)-is sorted to ILVs in an ESCRT-independent manner, where it is proteolytically processed and assembled into functional amyloid fibrils during melanosome maturation. Here we show that the tetraspanin CD63 directly participates in ESCRT-independent sorting of the PMEL luminal domain, but not of traditional ESCRT-dependent cargoes, to ILVs. Inactivating CD63 in cell culture or in mice impairs amyloidogenesis and downstream melanosome morphogenesis. Whereas CD63 is required for normal PMEL luminal domain sorting, the disposal of the remaining PMEL transmembrane fragment requires functional ESCRTs but not CD63. In the absence of CD63, the PMEL luminal domain follows this fragment and is targeted for ESCRT-dependent degradation. Our data thus reveal a tight interplay regulated by CD63 between two distinct endosomal ILV sorting processes for a single cargo during LRO biogenesis.

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    • "Impaired formation of PMEL fibrilogenesis upon ApoE deficiency is not due to a defect of PMEL cleavage since ratio between proteolytic PMEL fragments remained unchanged after ApoE depletion (Figure S5A); but it could be linked to PMEL sorting to ILVs since siRNA-mediated depletion of ApoE reduced the association of ApoE and PMEL luminal domain to ILVs that are released as exosomes (Figure 5A). This defect of PMEL sorting in ApoE-depleted cells echoed the observations made upon depletion of CD63, which regulates the ESCRT-I-independent sorting of the PMEL luminal domain on ILVs (van Niel et al., 2011). In agreement with a role of ApoE and CD63 in the same sorting pathway, partial siRNA-mediated depletion of CD63 (Figure S5B) induced a significant accumulation of ApoE in a perinuclear compartment (Figure 5B) that we identified by EM as the Golgi apparatus (Figure 5C). "
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    • "The sorting of EGFR onto ILVs depends on the endosomal sorting complexes required for transport (ESCRT) machinery (Doyotte et al., 2005; Razi and Futter, 2006). The sorting of the melanogenic-cell-specific protein PMEL onto ILVs is accompanied by proteolytic events that lead to the generation of fibrils within the immature melanosome upon which melanin is deposited (Berson et al., 2001), PMEL sorting to ILVs is ESCRT independent (Theos et al., 2006) but depends on the tetraspannin, CD63 (van Niel et al., 2011). In an oligodendroglial cell line, the sorting of the proteolipid protein onto ILVs that can subsequently be released as exosomes depends on the sphingomyelinase-dependent production of ceramide (Trajkovic et al., 2008). "
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