Intracellular transport and maturation of nascent low density lipoprotein receptor is blocked by mutation in the Ras-related GTP-binding protein, RAB1B.
The relationship between the Ras-related GTP-binding protein, Rab1B, and intracellular transport of nascent low density lipoprotein (LDL) receptor was studied in cultured human embryonic kidney cells (line 293) cotransfected with plasmids encoding the LDL-receptor and either wild-type Rab1B or a Rab1B mutant (N121I) known to act as a dominant suppressor of endogenous Rab1B function. [35S]Methionine pulse-chase analysis of immunoprecipitated LDL-receptor indicated that coexpression with Rab1BN121I, but not Rab1BWT, impaired its conversion from the Endo-H-sensitive 120-125 kDa form to the O-glycosylated 160-170 kDa form, consistent with a block in ER-->Golgi trafficking of the nascent receptor. In cells expressing Rab1BN121I, the newly synthesized LDL-receptor was unable to reach the cell surface as evidenced by its inaccessibility to sulfo-NHS-biotin added to the cultures. These observations provide a direct demonstration of Rab protein involvement in LDL receptor trafficking and lend support to the concept of Rab1B as a universal mediator of ER-->Golgi transport of membrane glycoproteins in mammalian cells.
Castellano
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F
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822-2616, USA.
Wilson
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AL
Maltese
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WA
D001483:Base Sequence; D001692:Biological Transport; D002461:Cell Line, Transformed; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology*; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D011973:Receptors, LDL / Q000378:metabolism*; D020761:rab1 GTP-Binding Proteins
D011973:Receptors, LDL; D019204:GTP-Binding Proteins; C061569:RAB1B protein, rat; D020761:rab1 GTP-Binding Proteins