Store-operated calcium entry (SOCE) is the main Ca 2؉ influx pathway involved in controlling proliferation of the human hepatoma cell lines Huh-7 and HepG2. However, the molecular nature of the calcium channels involved in this process remains unknown. Huh-7 and HepG2 cells express transient receptor potential canonical 1 (TRPC1) and TRPC6, as well as STIM1 and Orai1, and these 4 channels are the most likely candidates to account for the SOCE in these cells. We generated stable TRPC6-overexpressing or TRPC6-knockdown Huh-7 clones, in which we investigated correlations between the presence of the protein, the rate of cell proliferation, and SOCE amplitude. TRPC6-overexpressing Huh-7 cells proliferated 80% faster than did untransfected cells and their SOCE amplitude was 160% higher. By contrast, proliferation rate was 50% lower and SOCE amplitude 85% lower in TRPC6-knockdown clones than in untransfected cells. OAG (olyl acetyl glycerol)-induced calcium entry was similar in all cells, and small interfering RNA (siRNA) against TRPC1 had no effect on SOCE amplitude, highlighting the relationship among SOCE, TRPC6 and cell proliferation in Huh-7 cells. SOCE amplitude was reduced by STIM1 and Orai1 knockdowns, suggesting possible cooperation between these proteins and TRPC6 in these cells. Endothelial growth factor and hepatocyte growth factor increased TRPC6 expression and SOCE amplitude in Huh-7 cells, and cyclin D1 expression was decreased by STIM1, Orai1, and TRPC6 knockdowns. Conclusion: TRPC6 was very weakly expressed in isolated hepatocytes from healthy patients and expressed more strongly in tumoral samples from the liver of a cancer patient, strongly supporting a role for these calcium channels in liver oncogenesis. (HEPATOLOGY 2008;47:2068-2077 T he processes involved in the transformation of normal cells into tumorigenic cells and tumor progression are complex and only partially understood. 1,2 Many proteins in cancer cells are produced in larger or smaller amounts than in normal cells. Some of these proteins associated with cancer progression are involved in calcium homeostasis. Several types of cancer cells require an influx of calcium to proliferate, and it has been known for more than 30 years that the proliferation and growth of normal vertebrate cells depend on the physiological concentration of extracellular calcium. 3,4 Calcium influx is required at various stages of the cell cycle, 4 but little is known about the nature of the calcium channels involved in this process in nonexcitable cells such as liver cells. Two separate calcium entry pathways are simultaneously activated in liver cells. Phospholipase C stimulation results in InsP3 and diacylglycerol (DAG) generation, leading to capacitative or store-operated calcium entry (SOCE) because of a decrease in the calcium concentration of the endoplasmic reticulum (ER) lumen. A second type of calcium channel, activated independently of store depletion by the membrane-permeant analogue of DAG, 1-oleoy-2-acetyl-glycerol (OAG), 5 has also been described an...

How renal epithelial cells respond to increased pressure and the link with kidney disease states remain poorly understood. Pkd1 knock out or expression of a PC2 pathogenic mutant, mimicking the autosomal dominant polycystic kidney disease, dramatically enhances mechanical stress-induced tubular apoptotic cell death. We show the presence of a stretch-activated K+ channel dependent on the TREK-2 K2P subunit in proximal convoluted tubule epithelial cells. Our findings further demonstrate that polycystins protect renal epithelial cells against apoptosis in response to mechanical stress and this function is mediated through the opening of stretch-activated K2P channels. Thus, we establish for the first time, both in vitro and in vivo, a functional relationship between mechanotransduction and mechanoprotection. We propose that this mechanism is at play in other important pathologies associated with apoptosis and in which pressure or flow stimulation is altered, including heart failure or atherosclerosis.

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