Caveolin-1 directly interacts with UT-A1 urea transporter: the role of caveolae/lipid rafts in UT-A1 regulation at the cell membrane.
The cell plasma membrane contains specialized microdomains called lipid rafts which contain high amounts of sphingolipids and cholesterol. Lipid rafts are involved in a number of membrane protein functions. The urea transporter UT-A1, located in the kidney inner medullary collecting duct (IMCD), is important for urine concentrating ability. In this study, we investigated the possible role of lipid rafts in UT-A1 membrane regulation. Using sucrose gradient cell fractionation, we demonstrated that UT-A1 is concentrated in the caveolae-rich fraction both in stably expressing UT-A1 HEK293 cells and in freshly isolated kidney IMCD suspensions. In these gradients, UT-A1 at the cell plasma membrane is codistributed with caveolin-1, a major component of caveolae. The colocalization of UT-A1 in lipid rafts/caveolae was further confirmed in isolated caveolae from UT-A1-HEK293 cells. The direct association of UT-A1 and caveolin-1 was identified by immunoprecipitation and GST pull-down assay. Examination of internalized UT-A1 in pEGFP-UT-A1 transfected HEK293 cells fluorescent overlap with labeled cholera toxin subunit B, a marker of the caveolae-mediated endocytosis pathway. Disruption of lipid rafts by methyl-beta-cyclodextrin or knocking down caveolin-1 by small-interference RNA resulted in UT-A1 cell membrane accumulation. Functionally, overexpression of caveolin-1 in oocytes decreased UT-A1 urea transport activity and UT-A1 cell surface expression. Our results indicate that lipid rafts/caveolae participate in UT-A1 membrane regulation and this effect is mediated via a direct interaction of caveolin-1 with UT-A1.
Emory Univ. School of Medicine, Renal Division, WMRB Rm. 338, 1639 Pierce Drive, NE, Atlanta, GA 30322, USA.
Xiuyan
X
Feng
Haidong
H
Huang
Yuan
Y
Yang
Otto
O
Fröhlich
Janet D
JD
Klein
Jeff M
JM
Sands
Guangping
G
Chen
D000818:Animals; D021941:Caveolae / Q000378:metabolism*; D051242:Caveolin 1 / Q000378:metabolism*; D002460:Cell Line; D004705:Endocytosis; D005786:Gene Expression Regulation / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D000096982:Urea Transporters
D051242:Caveolin 1; D026901:Membrane Transport Proteins; D000096982:Urea Transporters