RESUMO
Receptors internalized by endocytosis can return to the plasma membrane (PM) directly from early endosomes (EE; fast recycling) or they can traffic from EE to the endocytic recycling compartment (ERC) and recycle from there (slow recycling). How receptors are sorted for trafficking along these two pathways remains unclear. Here we show that autosomal recessive hypercholesterolemia (ARH) is required for trafficking of megalin, a member of the LDL receptor family, from EE to the ERC by coupling it to dynein; in the absence of ARH, megalin returns directly to the PM from EE via the connecdenn2/Rab35 fast recycling pathway. Binding of ARH to the endocytic adaptor AP-2 prevents fast recycling of megalin. ARH-mediated trafficking of megalin to the ERC is necessary for γ-secretase mediated cleavage of megalin and release of a tail fragment that mediates transcriptional repression. These results identify a novel mechanism for sorting receptors for trafficking to the ERC and link ERC trafficking to regulated intramembrane proteolysis (RIP) and expression of megalin.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Endocitose , Regulação da Expressão Gênica , Proteína-2 Relacionada a Receptor de Lipoproteína de Baixa Densidade/metabolismo , Proteólise , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transporte Vesicular/genética , Proteínas Adaptadoras de Transporte Vesicular/metabolismo , Animais , Dineínas/metabolismo , Endossomos/metabolismo , Ativação Enzimática , Técnicas de Silenciamento de Genes , Humanos , Proteína-2 Relacionada a Receptor de Lipoproteína de Baixa Densidade/genética , Mesotelina , Ligação Proteica , Transporte Proteico , Ratos , Fator de Transcrição AP-2/metabolismo , Transcrição Gênica , Proteínas rab de Ligação ao GTP/genética , Proteínas rab de Ligação ao GTP/metabolismoRESUMO
Lysophosphatidic acid (LPA) mediates diverse cellular responses through the activation of at least six LPA receptors--LPA(1-6,) but the interacting proteins and signaling pathways that mediate the specificity of these receptors are largely unknown. We noticed that LPA(1) contains a PDZ binding motif (SVV) identical to that present in two other proteins that interact with the PDZ protein GIPC. GIPC is involved in endocytic trafficking of several receptors including TrkA, VEGFR2, lutropin and dopamine D2 receptors. Here we show that GIPC binds directly to the PDZ binding motif of LPA(1) but not that of other LPA receptors. LPA(1) colocalizes and coimmunoprecipitates with GIPC and its binding partner APPL, an activator of Akt signaling found on APPL signaling endosomes. GIPC depletion by siRNA disturbed trafficking of LPA(1) to EEA1 early endosomes and promoted LPA(1) mediated Akt signaling, cell proliferation, and cell motility. We propose that GIPC binds LPA(1) and promotes its trafficking from APPL-containing signaling endosomes to EEA1 early endosomes and thus attenuates LPA-mediated Akt signaling from APPL endosomes.