Human retinoid X receptor alpha (hRXRalpha) plays a critical role in DNA binding and transcriptional activity through its heterodimeric association with several members of the nuclear receptor superfamily, including the vitamin D receptor (VDR). Several cancer cell lines derived from many tissues have been shown to be resistant to the growth inhibitory action of 1,25-dihydroxyvitamin D3, (1,25(OH)2D3), the biologically active metabolite of vitamin D3. In the malignant ras-transformed human keratinocyte cell line, HPK1Aras, 10--100 fold higher concentrations of 1,25(OH)2D3 are required than the non-malignant normal human epidermal keratinocytes to achieve comparable inhibition of cell growth. Here we show that in ras-transformed keratinocytes, ser260 of hRXRalpha is phosphorylated through the Ras-Raf-MAP kinase cascade. This phosphorylation event results in the inhibition of vitamin D signaling via VDR/hRXRalpha heterodimers. Strategies to reverse this resistance include the use of the MAP kinase inhibitor, PD098059, and a non-phosphorylatable hRXRalpha mutant, ala260, which completely abolishes RXR phosphorylation and restores the function of both 1,25(OH)2D3 and a specific RXR ligand, LG1069 (4-[1-(5,6,7,8-tetrahydro-3,5,5,8,8-pentamethyl-2-naphtalenyl)ethenyl]-benzoic acid). In addition, we show that a vitamin D analog with low calcemic activity (EB1089) is more potent than 1,25(OH)2D3 in inhibiting cancer cell growth in this system. Targeted therapy with selective analogs such as EB1089, in combination with the inhibition of phosphorylation of the RXR, could play a critical role in the therapeutic strategies of cancer biology. In addition, we also demonstrate that resistance to 1,25(OH)2D 3 can be acquired through genetic alterations in the VDR, implying that both components of the VDR/RXR heterodimer are potential targets for the induction of cellular resistance to 1,25(OH)2D3 and present two distinct mechanisms through which tumour cells can escape the growt
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36710 |
| Date | January 2000 |
| Creators | Solomon, Cynthia, 1974- |
| Contributors | Kremer, Richard (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001754409, proquestno: NQ64670, Theses scanned by UMI/ProQuest. |
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