1, 25(OH)<sub>2</sub>D<sub>3</sub> Inhibits Hepatocellular Carcinoma Development Through Reducing Secretion of Inflammatory Cytokines from Immunocytes

Abstract

Epidemiological and clinical studies have indicated that low vitamin D activity is not only associated with an increased cancer risk and a more aggressive tumor growth, but also connected with an aggravated liver damage caused by chronic inflammation. Meanwhile, increasing evidence has demonstrated that 1,25(OH)₂D₃ (the most biologically active metabolite of vitamin D) can inhibit inflammatory response in some chronic inflammatory associated cancer, which is considered to have the anti-tumor potency. However, the interaction between 1,25(OH)₂D₃ and inflammation during hepatocellular carcinoma (HCC) initiation and progression is not yet clear. Here, we report an anti-tumorigenesis effect of 1,25(OH)₂D₃ via decreasing inflammatory cytokine secretion in HCC and hypothesize the possible underlying mechanism. Firstly, we show that the enhanced tumor growth is associated with elevated inflammatory cytokine IL-6 and TNF-α in 1α(OH)ase gene-knockout mice. Secondly, 1,25(OH)₂D₃ can inhibit vitamin D receptor (VDR) shRNA interfered tumor cell growth through decreasing inflammatory cytokine secretion in vitro and in vivo. Finally, using p27(kip1) gene knock-out mouse model, we demonstrate that the effect of 1,25(OH)₂D₃ in inhibiting immune cell related inflammatory cytokine secretion, exerts in a p27(kip1) gene dependent way. Collectively, 1,25(OH)₂D₃ inhibits HCC development through up-regulating the expression of p27(kip1) in immune cell and reducing inflammatory cytokine production.