DnaJA4 is a SREBP-regulated chaperone involved in the cholesterol biosynthesis pathway.
Using subtractive hybridization technique in 3T3-L1 adipocytes overexpressing constitutively active SREBP2, we have identified a DnaJ/Hsp40 chaperone, DnaJA4, as a new SREBP-responsive gene. SREBP2 regulation was demonstrated by changes in DnaJA4 mRNA under conditions of altered sterol status that were strictly parallel to that of well-characterized SREBP targets (LDL receptor and HMG-CoA reductase). The role of SREBP2 was further established using adenoviral overexpression of a dominant negative SREBP2, which abolished cholesterol-regulated changes in DnaJA4 expression. To determine the functional significance of this regulation, DnaJA4 was overexpressed in COS cells, which induced a specific increase in the synthesis of cholesterol from acetate. We also observed that DnaJA4 overexpression increased the activity and the protein content of HMG-CoA reductase, the rate limiting enzyme in this pathway. At the molecular level, DnaJA4 overexpression did not alter HMG-CoA reductase stability or mRNA levels, suggesting a co-translational effect of the chaperone. In the DnaJ/Hsp40 family, DnaJA4 uniquely exhibited SREBP-regulated expression, and also responded to heat shock. Through its responsiveness to SREBP, and its stimulatory effect on cholesterol synthesis, the DnaJA4 chaperone can be viewed as a new player in cholesterol synthesis. These data suggest a link between molecular chaperones, heat stress and cholesterol synthesis.
Robichon
Céline
C
INSERM U671, Paris, F-75270 France.
Varret
Mathilde
M
Le Liepvre
Xavier
X
Lasnier
Françoise
F
Hajduch
Eric
E
Ferré
Pascal
P
Dugail
Isabelle
I
D041721:3T3-L1 Cells; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002784:Cholesterol / Q000096:biosynthesis*; D003001:Cloning, Molecular; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D025782:Hydroxymethylglutaryl-CoA-Reductases, NADP-dependent / Q000378:metabolism; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism*
C494640:Dnaja4 protein, mouse; D050956:HSP40 Heat-Shock Proteins; D018832:Molecular Chaperones; D012333:RNA, Messenger; C497390:SREBF2 protein, human; D051782:Sterol Regulatory Element Binding Protein 2; D002784:Cholesterol; D025782:Hydroxymethylglutaryl-CoA-Reductases, NADP-dependent