Normal hepatic cell surface localization of the high density lipoprotein receptor, scavenger receptor class B, type I, depends on all four PDZ domains of PDZK1.
PDZK1 is a four PDZ domain-containing scaffold protein that binds to scavenger receptor class B, type I (SR-BI), the high density lipoprotein receptor, by its first PDZ domain (PDZ1). PDZK1 knock-out mice exhibit a >95% decrease in hepatic SR-BI protein and consequently an approximately 70% increase in plasma cholesterol in abnormally large high density lipoprotein particles. These defects are corrected by hepatic overexpression of full-length PDZK1 but not the PDZ1 domain alone, which partially restores SR-BI protein abundance but not cell surface expression or function. We have generated PDZK1 knock-out mice with hepatic expression of four PDZK1 transgenes encoding proteins with nested C-terminal truncations: pTEM, which lacks the three C-terminal residues (putative PDZ-binding motif), and PDZ1.2, PDZ1.2.3, or PDZ1.2.3.4, which contain only the first two, three, or four N-terminal PDZ domains, respectively, but not the remaining C-terminal sequences. Hepatic overexpression of pTEM restored normal hepatic SR-BI abundance, localization, and function. Hepatic overexpression of PDZ1.2 or PDZ1.2.3 partially restored SR-BI abundance ( approximately 12 or approximately 30% of wild type, respectively) but did not (PDZ1.2) or only slightly (PDZ1.2.3) restored hepatic SR-BI cell surface localization and function. Hepatic overexpression of PDZ1.2.3.4 completely restored SR-BI protein abundance, cell surface expression, and function (normalization of plasma cholesterol levels). Thus, all four PDZ domains in PDZK1, but not PDZ1-3 alone, are sufficient for its normal control of the abundance, localization, and therefore function of hepatic SR-BI, whereas the residues C-terminal to the PDZ4 domain, including the C-terminal putative PDZ-binding domain, are not required.
Fenske
Sara A
SA
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Yesilaltay
Ayce
A
Pal
Rinku
R
Daniels
Kathleen
K
Barker
Caroline
C
Quiñones
Verónica
V
Rigotti
Attilio
A
Krieger
Monty
M
Kocher
Olivier
O
D000818:Animals; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism*; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D008074:Lipoproteins / Q000032:analysis; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D054731:PDZ Domains / Q000502:physiology*; D019076:Transgenes / Q000502:physiology
D018955:CD36 Antigens; D047908:Intracellular Signaling Peptides and Proteins; D008074:Lipoproteins; D008565:Membrane Proteins; C514896:PDZK1 protein, mouse