Comparative effect of sodium butyrate and sodium propionate on proliferation, cell cycle and apoptosis in human breast cancer cells MCF-7.

INTRODUCTION: Short-chain fatty acids (SCFAs) are ubiquitous lipids produced as a result of bacterial fermentation of dietary fiber. While their role in colorectal cancer is well known, the effect of SCFAs in breast cancer is poorly defined. OBJECTIVE: To understand the various effects of SCFAs on breast carcinogenesis, we investigated the effect of sodium butyrate (NaB) and sodium propionate (NaP) in MCF-7 cell line. MATERIALS AND METHODS: Cells were incubated with different concentrations of NaB or NaP for 24, 48, 72 or 96 h. Cell proliferation was assayed using MTT kit. Cell cycle was performed using propidium iodide staining then analyzed with a flow cytometer. Apoptosis was assessed by Hoechst technique and cell-cycle sub-G1 phase. RESULTS: NaB and NaP inhibited MCF-7 cell proliferation in a dose-dependent manner with respective IC50 of 1.26 mM and 4.5 mM, thus indicating that NaB is more potent than NaP. Low and medium levels of both SCFAs induced morphology changes which are characteristic of a differentiated phenotype. Flow cytometry analysis revealed a blockage in G1 growth phase. Interestingly, removing NaB or NaP from culture media after few days of treatment showed a reversible effect on cell morphology and proliferation where cells reentered the cycle after 24 h of drug wash-out. Finally, treatment with medium levels of these molecules induced low MCF-7 apoptosis, while higher doses led to massive apoptosis. CONCLUSION: Our results show that SCFAs may be considered as an interesting inhibitor for breast cancer progression.

TMEM33 regulates intracellular calcium homeostasis in renal tubular epithelial cells.

Mutations in the polycystins cause autosomal dominant polycystic kidney disease (ADPKD). Here we show that transmembrane protein 33 (TMEM33) interacts with the ion channel polycystin-2 (PC2) at the endoplasmic reticulum (ER) membrane, enhancing its opening over the whole physiological calcium range in ER liposomes fused to planar bilayers. Consequently, TMEM33 reduces intracellular calcium content in a PC2-dependent manner, impairs lysosomal calcium refilling, causes cathepsins translocation, inhibition of autophagic flux upon ER stress, as well as sensitization to apoptosis. Invalidation of TMEM33 in the mouse exerts a potent protection against renal ER stress. By contrast, TMEM33 does not influence pkd2-dependent renal cystogenesis in the zebrafish. Together, our results identify a key role for TMEM33 in the regulation of intracellular calcium homeostasis of renal proximal convoluted tubule cells and establish a causal link between TMEM33 and acute kidney injury.

Mechanoprotection by polycystins against apoptosis is mediated through the opening of stretch-activated K(2P) channels.

How renal epithelial cells respond to increased pressure and the link with kidney disease states remain poorly understood. Pkd1 knockout 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 K(2P) 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 K(2P) channels. Thus, to our knowledge, 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.

Differential roles of STIM1, STIM2 and Orai1 in the control of cell proliferation and SOCE amplitude in HEK293 cells.

Orai1, together with STIM1 and STIM2, constitutes the molecular basis for store-operated calcium entry (SOCE) and we have investigated their role in cell proliferation and cell cycle progression in HEK293 cells. 48-h serum deprival, and a 24-h treatment with 1 mM hydroxyurea or with 10 microM RO-3306--a cyclin-dependent kinase 1 inhibitor--induced cell cycle block in G1, S and G2/M, respectively. SOCE amplitude, monitored in whole-cell voltage clamped cells, was markedly reduced (60-70%) in all conditions, with full reversibility within 4h. Silencing of Orai and STIM1 using siRNA resulted in a large inhibition of SOCE (70-80%) whereas siSTIM2 had a smaller but significant effect (30%). However, the cell population doubling time was not affected in siSTIM1 cells (18 h, the same as in control cells) but was increased in both siOrai1 cells (29 h) and in siSTIM2 (23 h) even when combined with siSTIM1. This suggests that STIM1 plays no role in cell proliferation in HEK293 cells while STIM2 is involved in both SOCE and cell proliferation in these cells. Finally, the cell cycle block induced SOCE inhibition was associated with reduced Orai1 expression with full recovery within 4h, whereas the expression of STIM1 and STIM2 remained unaltered. These observations reveal a tight relation between cell proliferation, calcium entry and Orai1 expression in HEK293 cells.

Caveolae contribute to the apoptosis resistance induced by the alpha(1A)-adrenoceptor in androgen-independent prostate cancer cells.

BACKGROUND: During androgen ablation prostate cancer cells' growth and survival become independent of normal regulatory mechanisms. These androgen-independent cells acquire the remarkable ability to adapt to the surrounding microenvironment whose factors, such as neurotransmitters, influence their survival. Although findings are becoming evident about the expression of alpha(1A)-adrenoceptors in prostate cancer epithelial cells, their exact functional role in androgen-independent cells has yet to be established. Previous work has demonstrated that membrane lipid rafts associated with key signalling proteins mediate growth and survival signalling pathways in prostate cancer cells. METHODOLOGY/PRINCIPAL FINDINGS: In order to analyze the membrane topology of the alpha(1A)-adrenoceptor we explored its presence by a biochemical approach in purified detergent resistant membrane fractions of the androgen-independent prostate cancer cell line DU145. Electron microscopy observations demonstrated the colocalization of the alpha(1A)-adrenoceptor with caveolin-1, the major protein component of caveolae. In addition, we showed that agonist stimulation of the alpha(1A)-adrenoceptor induced resistance to thapsigargin-induced apoptosis and that caveolin-1 was necessary for this process. Further, immunohistofluorescence revealed the relation between high levels of alpha(1A)-adrenoceptor and caveolin-1 expression with advanced stage prostate cancer. We also show by immunoblotting that the TG-induced apoptosis resistance described in DU145 cells is mediated by extracellular signal-regulated kinases (ERK). CONCLUSIONS/SIGNIFICANCE: In conclusion, we propose that alpha(1A)-adrenoceptor stimulation in androgen-independent prostate cancer cells via caveolae constitutes one of the mechanisms contributing to their protection from TG-induced apoptosis.

Capacitative calcium entry and transient receptor potential canonical 6 expression control human hepatoma cell proliferation.

UNLABELLED: 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.