Staurosporine synergistically potentiates the deoxycholate-mediated induction of COX-2 expression.

Colorectal cancer is a major cause of cancer-related death in western countries, and thus there is an urgent need to elucidate the mechanism of colorectal tumorigenesis. A diet that is rich in fat increases the risk of colorectal tumorigenesis. Bile acids, which are secreted in response to the ingestion of fat, have been shown to increase the risk of colorectal tumors.

Importance of uncharged polar residues and proline in the proximal two-thirds (Pro107-Ser128) of the highly conserved region of mouse ileal Na+-dependent bile acid transporter, Slc10a2, in transport activity and cellular expression.

Background: SLC10A2-mediated reabsorption of bile acids at the distal end of the ileum is the first step in enterohepatic circulation. Because bile acids act not only as detergents but also as signaling molecules in lipid metabolism and energy production, SLC10A2 is important as the key transporter for understanding the in vivo kinetics of bile acids. SLC10A family members and the homologous genes of various species share a highly conserved region corresponding to Gly104-Pro142 of SLC10A2.

Ursodeoxycholic acid protects colon cancer HCT116 cells from deoxycholic acid-induced apoptosis by inhibiting apoptosome formation.

We previously demonstrated that ursodeoxycholic acid (UDC) requires prolonged (≥5 h) preincubation to exhibit effective protection of colon cancer HCT116 cells from deoxycholic acid (DC)-induced apoptosis. Although UDC diminished DC-mediated caspase-9 activation, cytochrome c release from the mitochondria was not inhibited, indicating that UDC acts on the steps of caspase-9 activation. In the present study, therefore, we investigated the effects of UDC on the factors involved in caspase-9 activation.

Mutational analysis of uncharged polar residues and proline in the distal one-third (Thr130-Pro142) of the highly conserved region of mouse Slc10a2.

Solute carrier family member 2 (SLC10A2) reabsorbs bile acids at the distal terminus of the ileum in an Na(+)-dependent manner. Alignment of deduced amino acid sequences of SLC10 family members and homologous genes in various species revealed a highly conserved region that corresponds to Gly(104)-Pro(142) of SLC10A2. To elucidate the functional importance of this region, uncharged polar residues and Pro in the distal one-third of this region in mouse Slc10a2 (mSlc10a2) were submitted to mutational analysis, and taurocholic acid uptake and cell surface localization were evaluated.

Biphasic regulation of cell death and survival by hydrophobic bile acids in HCT116 cells.

A secondary bile acid, namely, deoxycholic acid (DCA), has been known to promote colon tumors; on the other hand, it also induces apoptosis in several human colon cancer cell lines. A hydrophobic primary bile acid, namely, chenodeoxycholic acid (CDCA), exhibits a similar property of apoptosis induction; DCA and CDCA also trigger some specific intracellular signal pathways in the human colon cancer cell line HCT116. In this article, we report that hydrophobic bile acids induce different cellular responses depending on their concentration, that is, a sublethal concentration of hydrophobic bile acids can suppress the apoptosis induced by a higher concentration of DCA.

Soybean resistant protein elevates fecal excretion of cholesterol and bile acids and decreases hepatic cholesterol content in comparison with soybean protein isolate.

The effect of soybean resistant protein (RP) on serum and hepatic cholesterol levels and fecal excretion of steroids was examined. RP decreased cholesterol in the liver, probably due to the stimulated excretion of cholesterol and its metabolites, bile acids. The serum cholesterol level was not different as between RP and other soy-derived proteins.

Deoxycholic acid can induce apoptosis in the human colon cancer cell line HCT116 in the absence of Bax.

In the human colon cancer cells HCT116, deoxycholic acid (DCA) induces apoptosis via the mitochondrial pathway by triggering the release of mitochondrial factors such as cytochrome c. To elucidate if Bax, a proapoptotic member of the Bcl-2 family known to trigger cytochrome c release in response to various types of apoptotic stimuli, is involved in DCA-induced apoptosis in HCT116 cells, we analyzed DCA-induced apoptosis in Bax-knockout (Bax(-/-)) HCT116 cells. Cytochrome c release and caspase-9 activation were detectable after 5 min in both Bax(-/-) and Bax(+/-) HCT116 cells.

Excess leucine intake induces serine dehydratase in rat liver.

We have hypothesized that rat liver serine dehydratase (SDH) is induced in response to the amount of surplus amino acids from dietary protein. In the present study, we found that excess leucine intake strongly induced SDH activity in the liver but not in the kidney of rats. The increase in activity was accompanied by increases in the levels of SDH mRNA.

Effects of Ala substitution for conserved Cys residues in mouse ileal and hepatic Na+-dependent bile acid transporters.

Although ileal and hepatic Na(+)-dependent bile acid transporters (SLC10A2 and SLC10A1 respectively) share structural similarities, the mutation of conserved amino acids often has distinct effects on them. We have identified two Cys residues in mouse Slc10a2 (Cys(51) and Cys(106)) the replacement of which by Ala remarkably reduces taurocholic acid (TCA) transport. Although Cys(51) is conserved in Slc10a1 as Cys(44), Ala substitution gave no apparent difference in TCA uptake.

Taurocholic acid does not induce apoptosis in HCT116 cells regardless of its intracellular concentration.

Hydrophobic bile acids but not hydrophilic bile acids induce apoptosis in HCT116 cells. We expressed sodium-dependent bile acid transporters in HCT116 cells, and the intracellular concentration of hydrophilic bile acids increased to that of the hydrophobic bile acids. But no sign of apoptosis was observed, which suggests a hydrophobic-bile acid-specific mechanism for the induction of apoptosis in HCT116 cells.

Evidence for the existence of a soybean resistant protein that captures bile acid and stimulates its fecal excretion.

Feeding HMF, an insoluble "high-molecular-weight fraction" from an industrial enzymatic digest of a soy protein isolate, increased the fecal excretion of bile acid concomitant with increased fecal nitrogen. An amino acid analysis revealed that this increased fecal nitrogen could be explained by an increase in the insoluble protein fraction. This suggests the existence of an indigestible protein or peptide that can be called a "resistant protein" in the feces.

Characteristics of apoptosis in HCT116 colon cancer cells induced by deoxycholic acid.

Hydrophobic bile acids induce apoptosis in both colon cancer cells and hepatocytes. The mechanism by which colon cancer cells respond to bile acids is thought to be different from that of hepatocytes. Therefore, we investigated the characteristics of apoptosis in colon cancer cell line HCT116.

Inverse correlation between the nitrogen balance and induction of rat liver serine dehydratase (SDH) by dietary protein.

Rats of different ages (3 to 15-wk-old) were fed on a 25% casein diet for one week, and the nitrogen balance and liver serine dehydratase (SDH, EC 4.2.1.

ATP hydrolysis-dependent multidrug efflux transporter: MDR1/P-glycoprotein.

P-glycoprotein/MDR1 was the first member of the ATP-binding cassette (ABC) transporter superfamily to be identified in a eukaryote. In eukaryotes, ABC proteins can be classified into three major groups based on function: transporters, regulators, and channels. MDR1/P-glycoprotein is a prominent member of eukaryotic export-type ABC proteins.

Postprandial changes in portal venous free amino acids and insulin/glucagon ratios as the result of protein over-intake are not directly linked to serine dehydratase induction in rat liver irrespective of age.

The activity of hepatic serine dehydratase (SDH) increases in tandem with its gene expression when the intake of protein greatly exceeds protein requirements. The actual conditions of plasma free amino acids and pancreatic hormones in weanling and mature rats when fed SDH-inducible and non-inducible diets were examined in relation to incentive factors to secure high SDH activity from a physiological standpoint. Both weanling and mature groups differing in protein requirements were allowed free access to respective diets diverse in protein content (i.

Quantity as well as quality of dietary protein affects serine dehydratase gene expression in rat liver.

Weanling rats were fed respective diets diverse in protein source and content for a full week, and hepatic serine dehydratase (SDH) was examined for its gene expression and activity induction attendant on high protein intake. The protein sources used were three kinds of milk casein, codfish meat, and wheat gluten. The body weight gain (% augmentation/wk) increased with increasing protein intake and reached a plateau in both milk casein- and codfish meat-fed rats by protein intake above 2.

Response of the induction of rat liver serine dehydratase to changes in the dietary protein requirement.

Growing and mature rats were examined for the effect of a change in dietary protein requirements on the induction of liver serine dehydratase (SDH). The rats were fed on diets varying in casein content, and the weight change and nitrogen balance was determined. SDH activity and its gene expression were induced in both growing and mature rats when their protein intake exceeded their nutritional requirements.

Inhibition of the multidrug resistance protein 1 (MRP1) by peptidomimetic glutathione-conjugate analogs.

Inhibition of multidrug resistance protein 1 (MRP1) mediated cytostatic drug efflux might be useful in the treatment of drug resistant tumors. Because the glutathione (GSH) conjugate of ethacrynic acid (EA), GS-EA, is a good substrate of MRP1, GS-EA derivatives are expected to be good inhibitors of MRP1. To study structure-activity relationships of MRP1 inhibition, a series of novel GS-EA analogs was synthesized in which peptide bonds of the GSH backbone were replaced by isosteric groups [Bioorg Med Chem 10:195-205, 2002].

Transport of bile acids in multidrug-resistance-protein 3-overexpressing cells co-transfected with the ileal Na+-dependent bile-acid transporter.

Many of the transporters involved in the transport of bile acids in the enterohepatic circulation have been characterized. The basolateral bile-acid transporter of ileocytes and cholangiocytes remains an exception. It has been suggested that rat multidrug resistance protein 3 (Mrp3) fulfills this function.

Characterization of cloned mouse Na+/taurocholate cotransporting polypeptide by transient expression in COS-7 cells.

The mouse Na+/taurocholate cotransporting polypeptide transiently expressed in COS-7 cells caused sodium-dependent uptake of [3H]taurocholic acid with Km and Vmax values of 18 microM and 102 pmol/mg protein/min, respectively. This Km value is comparable to that for rat NTCP and higher than that for human NTCP. Substrate specificity was evaluated by measuring inhibitory effects of unlabeled bile acids on [3H]taurocholic acid transport.

Effects of Cys mutation on taurocholic acid transport by mouse ileal and hepatic sodium-dependent bile acid transporters.

All cysteines of mouse ileal and hepatic sodium-dependent bile acid transporters (Isbt and Ntcp, respectively) were individually replaced by alanine. Replacement of Cys106 in Isbt and Cys96 in Ntcp, which are located closely in alignment, decreased taurocholate uptake. Although Cys51 in Isbt is conserved in Ntcp, the replacement spoiled Isbt only.