Evidence for b0,+-type amino acid transporter 1 association with caveolin-1 and ?

초록

Two type II membrane glycoproteins with single transmembrane domains have been implicated in amino acid transport via the plasma membrane. The first is rBAT (related to b0,+ amino acid transporter). It induces the Na+-independent transport of cystine as well as basic and neutral amino acids. The second one is 4F2hc (the heavy chain of the 4F2 antigen), which was originally identified as a cell surface antigen. It also induces amino acid transport when expressed in Xenopus oocytes. Recent results show transporters for amino acid transport systems L, y+L and x-C were 4F2hc light chains which require 4F2hc for their functional expression. In addition, it was reported that BAT1 was light chain of BAT. From substrate specificity, BAT1 transports cystine as well as arginine. Arginine was good substrate of cationic amino acid transporter (CAT). And the function of CAT was regulated by caveolin. In this connection, we studied the relationship between BAT1 and caveolins in the rat kidney using RT-PCR and Western blotting. The expression of BAT, BAT1, CAV-1, -2 and ? was investigated in rat kidney. BAT1 and BAT protein were observed in cortex and outer medulla of kidney, respectively. In the case of caveolins, caveolin-1 and ? proteins were detected in cortex, outer medulla and inner medulla. In contrast, caveolin-3 was not detected in kidney. To clarify the association of caveolin and BAT1, Western blot analysis was performed using isolated caveolae. Caveolin-1, -2, BAT and BAT1 were located in caveolae (#3 and 4). For the direct evidence of association between BAT1 and caveolin, immunoprecipitaion result showed BAT1 was bound to caveolin-1 and ?. In addition, the immunocytochemistry data also support these results. From these results, BAT1 was associated with caveolins and the further study on functional regulation of caveolins over the function of BAT1 should be needed.