24R,25(OH)₂D₃ regulates tumorigenesis in estrogen sensitive laryngeal cancer cells via membrane‐associated receptor complexes in ER+ and ER− cells

This study examined the effects of 24R,25‐dihydroxyvitamin D 3 (24R,25(OH) 2 D 3 ) in estrogen‐responsive laryngeal cancer tumorigenesis in vivo, the mechanisms involved, and whether the ability of the tumor cells to produce 24R,25(OH) 2 D 3 locally is estrogen‐dependent. Estrogen receptor alpha‐66 positive (ER+) UM‐SCC‐12 cells and ER− UM‐SCC‐11A cells responded differently to 24R,25(OH) 2 D 3 in vivo; 24R,25(OH) 2 D 3 enhanced tumorigenesis in ER+ tumors but inhibited tumorigenesis in ER− tumors. Treatment with 17β‐estradiol (E 2 ) for 24 h reduced levels of CYP24A1 protein but increased 24R,25(OH) 2 D 3 production in ER+ cells; treatment with E 2 for 9 min reduced CYP24A1 at 24 h and reduced 24R,25(OH) 2 D 3 production in ER− cells. These findings suggest the involvement of E 2 receptor(s) in addition to ERα66. To investigate if 24R,25(OH) 2 D 3 can act locally, ER+ and ER− cells were treated with 24R,25(OH) 2 D 3 after inhibiting putative 24R,25(OH) 2 D 3 receptors, and the cells were assessed for effects on DNA synthesis (proliferation) and p53 production (apoptosis). Specific inhibitors were used to assess downstream secondary messenger signaling pathways and requirements for palmitoylation and caveolae in both cell lines. The results show that 24R,25(OH) 2 D 3 binds to a complex of receptors, including TLCD3B2, VDR, and protein disulfide‐isomerase A3 (PDIA3) in ER+ UM‐SCC‐12 cells. The mechanism requires palmitoylation, and PLD, PI3K, and LPAR are involved. The anti‐tumorigenic effects of 24R,25(OH) 2 D 3 in ER− UM‐SCC‐11A cells involve a membrane‐receptor complex consisting of VDR, PDIA3, and ROR2 within caveolae to activate a yet‐to‐be‐elucidated downstream signaling cascade. This work demonstrates a driving mechanism for the therapeutic agent 24R,25(OH) 2 D 3 that may be used for laryngeal cancer patients.