Intracellular transport and maturation of nascent low density lipoprotein receptor is blocked by mutation in the ras-related GTP-binding protein, rabib

Abstract

The relationship between the Ras-related GTP-binding protein, Rab 1 B, and intracellular transport of nascent low density lipoprotein (LDL) eceptor was studied in cultured human embryonic kidney cells (line 293) otransfected with plasmids encoding the LDL-receptor and either wild-type Rab 1 B or a Rab 1 B mutant (N1211) known to act as a dominant suppressor of ndogenous Rab 1 B function. [³⁵S]Methionine pulse-chase analysis of mmunoprecipitated LDL-receptor indicated that coexpression with Rab 1 B^N1211 but not Rab l B^WT, 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 Rab 1 B^N1211, 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 Rab 1 B as a [niversal mediator of ER Golgi transport of membrane glycoproteins in mammalian cells.