Prostate cancer cell type-specific involvement of the VDR and RXR in regulation of the human PTHrP gene via a negative VDRE.
Parathyroid hormone-related protein (PTHrP) increases the growth and osteolytic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. We show that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its non-hypercalcemic analog, EB1089, decrease PTHrP mRNA and cellular protein levels in the androgen-dependent human prostate cancer cell line LNCaP and its androgen-independent derivative, the C4-2 cell line. This effect is mediated via a negative Vitamin D response element (nVDREhPTHrP) within the human PTHrP gene and involves an interaction between nVDREhPTHrP and the Vitamin D receptor (VDR). The retinoid X receptor (RXR) is a frequent heterodimeric partner of the VDR. We show that RXRalpha forms part of the nuclear protein complex that interacts with nVDREhPTHrP along with the VDR in LNCaP and C4-2 cells. We also show that the RXR ligand, 9-cis-retinoic acid, downregulates PTHrP mRNA levels; this decrease is more pronounced in LNCaP than in C4-2 cells. In addition, 9-cis-retinoic acid enhances the 1,25(OH)2D3-mediated downregulation of PTHrP expression in both cell lines; this effect also is more pronounced in LNCaP cells. Proliferation of LNCaP, but not C4-2, cells is decreased by 9-cis-retinoic acid. Promoter activity driven by nVDREhPTHrP cloned upstream of the SV40 promoter and transiently transfected into LNCaP and C4-2 cells is downregulated in response to 1,25(OH)2D3 and EB1089 in both cell lines. Co-treatment with these compounds and 9-cis-retinoic acid further decreases CAT activity in LNCaP, but not C4-2, cells. These results indicate that PTHrP gene expression is regulated by 1,25(OH)2D3 in a cell type-specific manner in prostate cancer cells.
Sepulveda
Veronica A Tovar
VA
Department of Pharmacology and Toxicology, and Sealy Center for Molecular Science, University of Texas Medical Branch, 10th and Market Streets, Galveston, TX 77555, USA.
Weigel
Nancy L
NL
Falzon
Miriam
M
D000077556:Alitretinoin; D002117:Calcitriol / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D044162:Parathyroid Hormone-Related Protein / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D018167:Receptors, Calcitriol / Q000187:drug effects / Q000378:metabolism*; D047488:Retinoid X Receptors / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D030181:Vitamin D Response Element / Q000502:physiology*
D044162:Parathyroid Hormone-Related Protein; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D047488:Retinoid X Receptors; D000077556:Alitretinoin; D014212:Tretinoin; D002117:Calcitriol; C078903:seocalcitol