Anti-proliferative action of vitamin D in MCF7 is still active after siRNA-VDR knock-down.
BACKGROUND
The active form of Vitamin D, 1,25-dihydroxyvitamin D3 (1,25D), has strong anti-proliferative effects, yet the molecular mechanisms underneath this effect remain unclear. In contrast, the molecular mechanism of 1,25D for the regulation of calcium homeostasis has principally been resolved, demonstrating a pivotal role for the vitamin D receptor (VDR).


RESULTS
We first addressed the question whether the anti-proliferative effects of 1,25D are influenced by VDR. Knockdown of VDR by siRNA did not affect the anti-proliferative effects of 1,25D in MCF7 breast cancer cells. This unanticipated finding led us to take an alternative approach using genome wide screens to study the molecular mechanisms of 1,25D in proliferation. For that purpose, four independently developed and stable 1,25D resistant MCF7 cell lines were analyzed. Array CGH identified a copy number alteration in a region of 13.5 Mb at chromosome 11q13.4-14.1 common to all four 1,25D resistant cell lines. Expression arrays revealed that no single gene was differentially expressed between the sensitive and resistant cells, but multiple membrane receptor signaling pathways were altered in the 1,25D resistant cell lines. Importantly, in the genome wide experiments neither VDR, CYP24A1 nor other known vitamin D signaling pathway genes were associated with 1,25D resistance.


CONCLUSIONS
In conclusion, siRNA and genome wide studies both suggest that the anti-proliferative effects of 1,25D in MCF7 breast tumor cell lines do not rely on classical Vitamin D pathway per se.
Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands. jcosta@ipatimup.pt
José L
JL
Costa
Paul P
PP
Eijk
Mark A
MA
van de Wiel
Derk
D
ten Berge
Fernando
F
Schmitt
Carmen J
CJ
Narvaez
JoEllen
J
Welsh
Bauke
B
Ylstra
D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D018628:Gene Dosage / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006801:Humans; D034741:RNA, Small Interfering / Q000235:genetics*; D018167:Receptors, Calcitriol / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D014807:Vitamin D / Q000494:pharmacology*
D034741:RNA, Small Interfering; D018167:Receptors, Calcitriol; D014807:Vitamin D