Alix facilitates the interaction between c-Cbl and platelet-derived growth factor beta-receptor and thereby modulates receptor down-regulation.
Alix (ALG-2-interacting protein X) is an adaptor protein involved in down-regulation and sorting of cell surface receptors through the endosomal compartments toward the lysosome. In this study, we show that Alix interacts with the C-terminal region of the platelet-derived growth factor (PDGF) beta-receptor (PDGFRbeta) and becomes transiently tyrosine-phosphorylated in response to PDGF-BB stimulation. Increased expression levels of Alix resulted in a reduced rate of PDGFRbeta removal from the cell surface following receptor activation, and this was associated with decreased receptor degradation. Furthermore, Alix was found to co-immunoprecipitate with the ubiquitin ligase c-Cbl, and elevated Alix levels increased the interaction between c-Cbl and PDGFRbeta. Interestingly, Alix interacted constitutively with both c-Cbl and PDGFRbeta. Moreover, c-Cbl was found to be hyperphosphorylated in cells engineered to overexpress Alix compared with control cells. The increased c-Cbl phosphorylation correlated with enhanced proteasomal degradation of c-Cbl, which in turn correlated with a decreased ubiquitination of PDGFRbeta. Our data suggest that Alix inhibits down-regulation of PDGFRbeta by modulating the interaction between c-Cbl and the receptor, thereby affecting the ubiquitination of the receptor.
Lennartsson
Johan
J
Ludwig Institute for Cancer Research, Uppsala University, Biomedical Center, SE-751 24 Uppsala, Sweden.
Wardega
Piotr
P
Engström
Ulla
U
Hellman
Ulf
U
Heldin
Carl-Henrik
CH
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D015536:Down-Regulation; D056827:Endosomal Sorting Complexes Required for Transport; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013552:Swine; D014443:Tyrosine / Q000737:chemistry; D025801:Ubiquitin / Q000737:chemistry*
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D056827:Endosomal Sorting Complexes Required for Transport; C117020:PDCD6IP protein, human; D025801:Ubiquitin; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D020797:Receptor, Platelet-Derived Growth Factor beta; D046988:Proteasome Endopeptidase Complex