Our study is the first to show that in colonocytes inflammatory cytokines are able to upregulate CaSR expression, and that this effect is time- and cell line-specific. In the present study, we investigated the role of 1,25D3, TNFα, and IL-6 on the transcriptional and translational activation of the CaSR in two cell lines representing a highly differentiated and a moderately differentiated colorectal GS-7340 price tumor. 1,25D3 is known for its anti-proliferative, pro-differentiating effects (for review, see [22]), and its involvement in regulating epigenetic mechanisms [23]. Inducing expression of CaSR, a putative tumor suppressor

in the colon, might be one of the tumor preventive mechanisms Selleckchem Apoptosis Compound Library of 1,25D3. In the differentiated Caco2/AQ cells 1,25D3 had more pronounced impact in inducing the expression of CaSR than in the less differentiated Coga1A cells. In Caco2/AQ cells treatment with 1,25D3 reduced the expression of several proliferation markers also. This was much less evident in the Coga1A cells (data not shown), although the level of the vitamin D receptor is similar [15]. In Caco2/AQ cells, both TNFα and IL-6

increased CaSR expression to a lesser extent than 1,25D3. In combination, however, they caused a strong upregulation at 6 h, which was lost at 12 h; at 24 h the effect became additive and the CaSR level remained high also after 48 h. We hypothesized that two different

mechanisms were responsible: first, direct upregulation of CaSR expression due to a transient activation of CaSR promoters by NF-κB upon treatment with TNFα and Stat1/3 and Sp1/3 elements by IL-6. these This was followed by a second induction of transcription that seems to be indirect. Some (still unknown) factors induced by TNFα and IL-6 might be needed for this more stable induction of CaSR expression. Unexpectedly, 1,25D3 counteracted this additive effect, suggesting the existence of intricate feedback systems. In Coga1A cells, the CaSR was more sensitive to the proinflammatory cytokine TNFα, which was the main driver of CaSR expression in these cells. The low effectiveness of IL-6 in upregulating CaSR expression could be due to lower levels of the IL-6 receptor complex (both the IL-6 binding α chain and the signal transducing unit gp130) in Coga1A cells compared with Caco2/AQ [24]. Interestingly, in these cells the CaSR protein levels remained enhanced in all combined treatments. The robust increase of CaSR expression by TNFα treatment in Coga1A cells could be regarded as a defense mechanism against inflammation. Such protective mechanism was shown in murine macrophages, where lipopolysaccharide-induced TNFα release upregulated CaSR expression leading to inhibition of TNFα synthesis, in a negative feedback manner [25].