title: Calcitriol enhancement of TPA-induced tumorigenic transformation is mediated through vitamin D receptor-dependent and -independent pathways.
abstract: We previously showed that 1alpha,25-dihydroxyvitamin D3, calcitriol, enhanced phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induced tumorigenic transformation of mouse epidermal JB6 Cl41.5a cells. To determine if calcitriol regulates this enhancement through a nuclear vitamin D receptor (VDR)-dependent or -independent pathway, we used vitamin D analogs which induce biological responses by either of these mechanisms. In JB6 Cl41.5a cells, 1alpha,24-dihydroxy-22-ene-24-cyclopropyl-vitamin D3 (BT), which like calcitriol binds to VDR and regulates transcription, inhibited cell growth, stimulated expression of nonphosphorylated osteopontin (OPN), and enhanced TPA-induced anchorage-independent growth (AIG, an in vitro assay which highly correlates with tumorigenicity of these cells). 25-Hydroxy-16-ene-23-yne-vitamin D3 (AT), which stimulates calcium influx but has low affinity for VDR, had moderate effects on cell growth and expression of OPN. However, it enhanced TPA-induced tumorigenic transformation, though to a lesser extent than BT, thus suggesting that a VDR-independent mechanism is involved. Since 1alpha-hydroxylase activity was detected in JB6 cells, AT could be converted into 1alpha,25-dihydroxy-16-ene-23-yne-vitamin D3 (V), an analog which binds with high affinity to VDR, and could subsequently enhance TPA-induced AIG. To verify whether the VDR-independent pathway is involved in calcitriol enhancement of tumorigenic transformation, two additional VDR-independent analogs, 1alpha,25-dihydroxy-lumisterol3 (JN) and 24R,25-dihydroxyvitamin D3 (AS), were tested. The analog JN, which stimulates calcium transport and cannot be further hydroxylated at 1-carbon position, increased TPA-induced AIG, while AS, which inhibits calcium influx, did not. These studies suggest that a VDR-independent pathway, perhaps stimulation of calcium influx, and a VDR-dependent mechanism, which directly affects transcription, are involved in calcitriol's enhancement of TPA-induced tumorigenic transformation in JB6 Cl41.5a cells.
authors.affiliation: Department of Nutrition Sciences, University of Alabama at Birmingham, 35294-3360, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Chang
authors.forename: T F
authors.initials: TF
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Garretson
authors.forename: C W
authors.initials: CW
authors.lastname: Prince
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000378:metabolism; D000818:Animals; D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D000078404:Epidermal Cells; D051379:Mice; D053495:Osteopontin; D018167:Receptors, Calcitriol / Q000378:metabolism*; D012795:Sialoglycoproteins / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014162:Transfection; D014807:Vitamin D / Q000031:analogs & derivatives
chemical_list: D018167:Receptors, Calcitriol; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D053495:Osteopontin; D014807:Vitamin D; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D013755:Tetradecanoylphorbol Acetate