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Butyrate is a short chain fatty acid (SCFA) produced by bacterial fermentation of dietary fibers in the colon lumen which severely affects the proliferation of colon cancer cells in in vitro experiments. Although butyrate is able to interfere with numerous cellular targets including cell cycle regulator expression, little is known about butyrate metabolism and its possible involvement in its effect upon colon carcinoma cell growth. In this study, we found that HT-29 Glc 2/1 cells strongly accumulated and oxidized sodium butyrate without producing ketone bodies, nor modifying oxygen consumption nor mitochondrial ATP synthesis. HT-29 cells accumulated and oxidized sodium acetate at a higher level than butyrate. However, sodium butyrate, but not sodium acetate, reduced cell growth and increased the expression of the cell cycle effector cyclin D3 and the inhibitor of the G1/S cdk-cyclin complexes p21/WAF1/Cip1, demonstrating that butyrate metabolism downstream of acetyl-CoA synthesis is not required for the growth-restraining effect of this SCFA. Furthermore, HT-29 cells modestly incorporated the 14 C-labelled carbon from sodium butyrate into cellular triacylglycerols and phospholipids. This incorporation was greatly increased when d-glucose was present in the incubation medium, corresponding to the capacity of hexose to circulate in the pentose phosphate pathway allowing NADPH synthesis required for lipogenesis. Interestingly, when HT-29 cells were cultured in the presence of sodium butyrate, their capacity to incorporate 14 C-labelled sodium butyrate into triacylglycerols and phospholipids was increased more than twofold. In such experimental conditions, HT-29 cells when observed under an electronic microscope, were found to be characterized by an accumulation of lipid droplets in the cytosol. Our data strongly suggest that butyrate acts upon colon carcinoma cells upstream of acetyl-CoA synthesis. In contrast, the metabolism downstream of acetyl-CoA [i.e. oxidation in the tricarboxylic acid (TCA) cycle and lipid synthesis] likely acts as a regulator of butyrate intracellular concentration.Keywords: butyrate; metabolism; growth; colon carcinoma cells.Epidemiological studies generally suggest a protective role of dietary fibers in colon carcinogenesis [1]. Dietary fibers contained in vegetables, fruit and cereals are heterogeneous group of compounds with different physicochemical properties [2]. They escape digestion and are recovered in the colon lumen. The different proposed mechanisms of action in which fibers may protect against colorectal tumours development include the inactivation of carcinogenic substances, an increase in faecal bulk with shortening of the bowel transit time and a decreased contact time [3]. In the large intestine, fibers can undergo anaerobic fermentation by intestinal flora leading to the production of various metabolites including short chain fatty acids (SCFA, mainly acetate, propionate and butyrate). Among these three, butyrate has received much attention due to its ability to severely ...

SummaryThe genes encoding (2Fe-2S) plant-like ferredoxins were studied in the widely used cyanobacterium Synechocystis PCC6803. The fedI gene (ssl0020) coding for the most abundant ferredoxin product was found to be expressed strongly as a light-induced monocistronic transcript, whereas the other fed genes appeared to be silent (slr1828) or moderately expressed as polycistronic transcripts regulated by either light fluence (slr0150, negative control) or glucose availability (sll1382). fedI was found to be critical to Synechocystis PCC6803 viability in spite of slr0150, sll1382 or flavodoxin induction, even after the addition of glucose that compensates for the loss of photosynthesis. Nevertheless, fedI could be deleted from all chromosome copies in cells propagating a fedI gene (even of heterologous origin) on a replicating plasmid. This strain was used as the host for the subsequent introduction of fedI mutant alleles propagated on a second vector. Analysis of the fedI mutant strains generated after plasmid exchange showed that the C18-C85 disulphide bridge is not central either to the tight compaction of ferredoxin I or to its reduction by photosystem I and demonstrated that the length of the FedI carboxy terminus is important for effective PSI/FedI interactions. The plasmid-shuffling strategy presently described has general applicability for mutational analysis of essential genes in many organisms, as it is based on promiscuous plasmids.