Abstract 5314: Calcium mediated growth control in normal and transformed colon cells: A possible role of the calcium sensing receptor.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: Calcium (Ca2+) plays an important role in regulating proliferation of colonic epithelium. Epidemiological studies suggest an inverse correlation between dietary Ca2+ intake and colorectal cancer (CRC) risk. However in CRC, transformed cells lose their sensitivity to the tumour inhibiting effects of Ca2+. We have shown that the extracellular calcium-sensing receptor (CaSR) expression is lost in CRC and therefore hypothesized that the CaSR mediates the effect of Ca2+ in regulating proliferation. Methods: We investigated the expression of the CaSR and of a cluster of genes responsible for ‘triggering off’ proliferation (CDT1, CDC6, CDC45, MCM2-7, Geminin, known as replication licensing genes) at mRNA level by qRT-PCR in CRC samples and in their respective ‘normal’ adjacent mucosa (n=57). To study the effect of Ca2+ in normal colon physiology, we fed male and female C57BL/6 mice with a diet containing high (0.9%) or low (0.1%) levels of Ca2+ and assessed the influence of dietary Ca2+ on proliferation (immunohistochemistry staining and mRNA expression) and CaSR mRNA expression. Results and Discussion: In tumours we found the expression of CaSR significantly downregulated when compared with respective adjacent mucosa (p<0.001). All genes involved in replication licensing are significantly higher expressed (p<0.001) in these samples. Our data suggest that the loss of CaSR gives the tumour cells growth advantage. In the tumour samples we found negative correlation between CaSR and licensing factors (CDC45 (p<0.05, ρ=−0.265) and MCM6 (p<0.05, ρ=−0.262) reaching significance). Surprisingly, CaSR showed positive correlation with the licensing factors in the ‘normal’ mucosa (CDT1 (p<0.05, ρ=0.269), MCM2 (p<0.003, ρ=0.382) and MCM5 (p<0.001, ρ=0.490) reaching significance). These results are similar to our observation in the mouse study, where low dietary Ca2+ enlarged the proliferative zone of the crypts with no significant change in CaSR expression. Conclusion: We conclude that the CaSR might regulate the calcium-dependent inhibition of proliferation in normal colonocytes. Upregulation of CaSR is probably a defence mechanism of the normal colon to control epithelial growth and counteract hyper-proliferative signals. This control mechanism is lost in cancer where CaSR expression is downregulated. Citation Format: Abhishek Aggarwal, Julia Hobaus, Irfete Sh. Fetahu, Ildiko Mesteri, Eniko Kallay. Calcium mediated growth control in normal and transformed colon cells: A possible role of the calcium sensing receptor. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5314. doi:10.1158/1538-7445.AM2013-5314