Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C91
TRPM7 cation channel is overexpressed in human pancreatic ductal adenocarcinoma and is required for cancer cell migration
P. Rybarczyk1, M. Gautier1, F. Hague1, I. Dhennin-Duthille1, D. Chatelain2, J. Kerr-Conte3, F. Pattou3, H. Sevestre2,1, H. Ouadid-Ahidouch1
1. Laboratoire de Physiologie Cellulaire et Mol
Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a poor prognosis : mortality essentially equals incidence. Despite many advances in medicine, there is still a lack of early diagnostic biomarkers of PDAC as well as efficient therapeutical strategies in advanced cases. Indeed, surgery is currently the only hope for cure. Thus, a better understanding of the cellular and molecular mechanisms involved in the development and progression of PDAC is needed. The melastatin-related transient receptor potential 7 channel (TRPM7) is a non-selective cation channel which has been shown to regulate the cell proliferation in human head and neck (Jiang et al., 2007), breast (Guilbert et al., 2009) cancers and PDAC (Yee et al., 2010) as well as migration in nasopharyngeal cancer (Chen et al., 2010). However, the role of TRPM7 in PDAC progression is far from understood. TRPM7 expression was studied using quantitative RT-PCR and immunohistochemistry in human PDAC tissues in comparison with pancreatic exocrine tissues from healthy donors. TRPM7 activity was studied in BxPC-3 cell line by the whole-cell patch-clamp technique, and calcium/magnesium-imaging. The contribution of TRPM7 to cations entry was assessed using the Mn2+-quenching technique. Finally, TRPM7 physiopathological role was studied using MTT assays and cell migration tests in Boyden chambers. Our results showed that TRPM7 is overexpressed 13-fold in cancer tissues compared to the normal ones. Furthermore, TRPM7 staining was stronger in poorly differentiated PDAC samples than in well and moderately differentiated ones, suggesting a correlation between TRPM7 expression and PDAC progression. In BxPC-3 cell line, dialyzing the cytoplasm during the whole-cell recording with a 0-Mg2+ solution activated a non-selective current with a strong outward rectification. This cation current was inhibited by intracellular Mg2+ with a maximal inhibition for free-[Mg2+]i= 850µM. This magnesium inhibited cation current was dramatically inhibited by a siRNA targeting TRPM7 (siTRPM7) compared to scrambled siRNA. Mn2+-quenching of Fura-2 was decreased by siTRPM7 suggesting that TRPM7 contributes to divalent cations entry in BxPC-3 cells. Indeed, siTRPM7 induced a decrease of basal intracellular Mg2+ fuorescence ratio (F360nm/F380nm) but not of intracellular Ca2+. Finally, siTRPM7 decreased BxPC-3 cell migration by 55% without affecting the cell proliferation. Cell migration was fully restored by adding 1mM Mg2+ in culture media after siTRPM7 treatment. In conclusion, TRPM7 is overexpressed in PDAC and regulates pancreatic cell migration likely via a Mg2+-dependent mechanism. Since the TRPM7 expression is stronger in undifferentiated areas, we propose this channel as a potential biomarker of poor prognosis in PDAC.
Where applicable, experiments conform with Society ethical requirements