Anti-proliferative action of vitamin D in MCF7 is still active after siRNA-VDR knock-down

José L Costa,Joellen Welsh,Carmen J Narvaez,Fernando Schmitt,Derk Ten Berge,Mark A Van De Wiel,Bauke Ylstra,Paul P Eijk

doi:10.1186/1471-2164-10-499

Abstract

BackgroundThe 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).ResultsWe 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.ConclusionIn 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.

Highlights

The active form of Vitamin D, 1,25-dihydroxyvitamin D3 (1,25D), has strong antiproliferative effects, yet the molecular mechanisms underneath this effect remain unclear
While many known vitamin D response elements (VDREs)-containing genes contribute to calcium regulation (e.g. CYP24A1, osteocalcin and osteopontin), others are involved in cellular processes like proliferation and apoptosis (e.g. p21, c-fos, and Bcl2) [2,3,4]
Proliferation in 1,25D resistant and sensitive MCF7 cell lines vitamin D receptor (VDR) is essential for regulation of calcium homeostasis by 1,25D, but its role in the anti-tumor effects mediated by vitamin D signaling remains unclear

Summary

Introduction

The active form of Vitamin D, 1,25-dihydroxyvitamin D3 (1,25D), has strong antiproliferative effects, yet the molecular mechanisms underneath this effect remain unclear. 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). Strong anti-proliferative effects of 1,25-dihydroxyvitamin D3 (1,25D) have been demonstrated in a wide spectrum of solid cancers, in vitro and in animal models [1]. A link between 1,25D status and cancer has been demonstrated in epidemiological studies Together these data (page number not for citation purposes). The molecular mechanisms by which the 1,25D pathway exerts its anti-proliferative effects remain unclear. 1,25D mediates the maintenance of calcium homeostasis through activation of the vitamin D receptor (VDR), a ligand dependent transcription factor. For example a membrane bound VDR was proposed [5] and other forms of signaling outside the nucleus [6]

Methods

Results

Discussion

Conclusion