BAG1L enhances trans-activation function of the vitamin D receptor.
The vitamin D receptor (VDR) is a member of the steroid/retinoid receptor superfamily of nuclear receptors that has potential tumor-suppressive functions. We show here that VDR interacts with and is regulated by BAG1L, a nuclear protein that binds heat shock 70-kDa (Hsp70) family molecular chaperones. Endogenous BAG1L can be co-immunoprecipitated with VDR from prostate cancer cells (ALVA31; LNCaP) in a ligand-dependent manner. BAG1L, but not shorter non-nuclear isoforms of this protein (BAG1; BAG1M/Rap46), markedly enhanced, in a ligand-dependent manner, the ability of VDR to trans-activate reporter gene plasmids containing a vitamin D response element in transient transfection assays. Mutant BAG1L lacking the C-terminal Hsc70-binding domain suppressed (in a concentration-dependent fashion) VDR-mediated trans-activation of vitamin D response element-containing reporter gene plasmids, without altering levels of VDR or endogenous BAG1L protein, suggesting that it operates as a trans-dominant inhibitor of BAG1L. Gene transfer-mediated elevations in BAG1L protein levels in a prostate cancer cell line (PC3), which is moderately responsive to VDR ligands, increased the ability of natural (1alpha,25(OH)(2) vitamin D(3)) and synthetic (1alpha, 25-dihydroxy-19-nor-22(E)-vitamin D(3)) VDR ligands to induce expression of the VDR target gene, p21(Waf1), and suppress DNA synthesis. Thus, BAG1L is a direct regulator of VDR, which enhances its trans-activation function and improves tumor cell responses to growth-suppressive VDR ligands.
Guzey
M
M
Burnham Institute, La Jolla, California 92037 and RIGEB, MAM-TUBITAK, P. K. 21 Gebze 41 470, Kocaeli, Turkey.
Takayama
S
S
Reed
J C
JC
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002117:Calcitriol / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008297:Male; D008565:Membrane Proteins; D011401:Promoter Regions, Genetic; D018167:Receptors, Calcitriol / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D015534:Trans-Activators / Q000187:drug effects*; D014157:Transcription Factors / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
C091732:BCL2-associated athanogene 1 protein; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D008565:Membrane Proteins; D018167:Receptors, Calcitriol; D015534:Trans-Activators; D014157:Transcription Factors; D002117:Calcitriol