Biphasic Regulation of Cell Death and Survival by Hydrophobic Bile Acids in HCT116 Cells

Abstract

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. Pretreatment with DCA or CDCA at a concentration of < or = 200 microM for 8 h suppressed the apoptosis induced by 500 microM DCA in HCT116 cells. Under this condition, the association of caspase-9 and Apaf-1 and subsequent activation of caspase-9 were inhibited, but the release of cytochrome c from the mitochondria was not. At 200 microM, DCA and CDCA induced the phosphorylation of Akt and ERK1/2, although these phosphorylations do not appear to be indispensable for the cytoprotection. It is interpreted that prolonged exposure to sublethal concentrations of hydrophobic bile acids induces resistance to apoptosis, leading to promotion of colorectal tumorigenesis.

Bile acids in regulation of intestinal physiology

“…First, the concentration of bile acid to which cells are exposed is important, with lower concentrations stimulating proliferation and higher concentrations causing cell death. Second, cell membrane permeability is also a determining factor, with conjugated, hydrophilic bile acids generally having little or no proapoptotic activity and deconjugated, dehydroxylated bile acids being the most detrimental [16,17]. Multiple mechanisms underlie the effects of bile acids in promoting proliferation.…”

“…At relatively low concentrations, bile acids augment their effects on epithelial proliferation through inhibition of apoptosis [16], but at higher concentrations, they are proapoptotic. Apoptotic effects are directly related to bile acid hydrophobicity, with DCA, CDCA, and LCA being the most potent and hydrophilic bile acids having little or no effect [17].…”

Ursodeoxycholic Acid Protects Colon Cancer HCT116 Cells From Deoxycholic Acid-Induced Apoptosis by Inhibiting Apoptosome Formation

“…Unlike hydrophobic bile acids such as DC and CDC (7,8), UDC did not exhibit remarkably acute cytotoxicity. Although cell proliferation was suppressed in a concentration-dependent manner, the number of HCT116 cells did not decrease, even at the highest concentration (600 µM), after 24 h (Fig.…”

“…We have previously demonstrated that sublethal concentrations of hydrophobic bile acids protect HCT116 cells from the apoptosis induced by the hydrophobic bile acids themselves. Sublethal concentrations of bile acids effectively attenuated activation of caspase-9, whereas cytochrome c release from the mitochondria was not inhibited (8). Given that the association of procaspase-9 and Apaf-1 was reduced in the cytoprotective condition, we propose that sublethal concentrations of hydrophobic bile acids protect cells from apoptosis by inhibiting apoptosome formation.…”

“…The HCT116 cell line stably expressing inactive caspase-9 tagged with 6 × His at the C-terminus (Casp-9-C287A-His) was established as described previously (8). Cells were scraped into PBS, centrifuged for 5 min at 1,000 × g, and resuspended in lysis buffer (50 mM NaH 2 PO 4 , 300 mM NaCl, and 10 mM imidazole, pH 7.4).…”