Activation of caspases occurs downstream from radical oxygen species production, Bcl-xL down-regulation, and early cytochrome C release in apoptosis induced by transforming growth factor β in rat fetal hepatocytes

Abstract

Most of the morphologic changes that are observed in apoptotic cells are caused by a set of cysteine proteases (caspases) that are activated during this process. In previous works from our group we found that treatment of rat fetal hepatocytes with transforming growth factor ␤1 (TGF-␤1) is followed by apoptotic cell death. TGF-␤1 mediates radical oxygen species (ROS) production that precedes bcl-x L down-regulation, loss of mitochondrial transmembrane potential, release of cytochrome c, and activation of caspase-3 (Herrera et al., FASEB J 2001;15:741-751). In this work, we have analyzed how TGF-␤1 activates the caspase cascade and whether or not caspase activation precedes the oxidative stress induced by this factor. Our results show that TGF-␤1 activates at least caspase-3, -8, and -9 in rat fetal hepatocytes, which are not required for ROS production, glutathione depletion, bcl-x L down-regulation, and initial cytochrome c release. However, caspase activation mediates cleavage of Bid and Bcl-x L that could originate an amplification loop on the mitochondrial events. An interesting result is that transmembrane potential disruption occurs later than the initial cytochrome c release and is mostly blocked by the pan-caspase inhibitor Z-VAD.fmk, indicating that the decrease in mitochondrial transmembrane potential (⌬⌿m) may be a consequence of caspase activity rather than the mechanism by which TGF-␤ induces cytochrome c efflux.

Upregulation of two BH3-only proteins, Bmf and Bim, during TGFβ-induced apoptosis

“…Indeed, Bmf was able to interact with Bcl-X L in vitro (data not shown). In addition, similar to previous data demonstrating downregulation of Bcl-X L in TGFb-stimulated cells (Nass et al, 1996;Saltzman et al, 1998;Chipuk et al, 2001;Herrera et al, 2001b), we also detected Bcl-X L as one of the apoptotic genes downregulated by TGFb in the microarray. Furthermore, Bcl-X L protein levels in both AML12 (Figure 3b) and NMuMG (Figure 3d) cells were correspondingly lower in cells exposed to TGFb and were also dependent upon both Smad signalling and p38 activity (Figure 3b).…”

Role of Bax in quercetin-induced apoptosis in human prostate cancer cells

“…Although quercetin increased the Bad:Bcl-xL ratio, quercetin decreased the Bax:Bcl-xL ratio; thus, regulation of Bcl-xL protein levels seems to be, at least in part, caspase-dependent in LNCaP cells, which agrees with previous results in human hepatoma treated with quercetin [41]. Quercetin also increased Bax translocation from the cytosol to the mitochondrial membrane, an event that promotes apoptotic death [53]. This accords with the increased levels of total Bax found in other studies of fetal hepatocytes [53] as well as in studies of human lung [43], prostate [54], and liver [55] cancer cells.…”

Chronic inflammation and oxidative stress in human carcinogenesis

“…It is also possible that the oxidative stress induces cell necrosis through the release of cytochrome c and the depletion of ATP at mitochondrial level. 34,35 Peroxynitrite participates with the apoptotic program through the nitrosylation of proteins, which in turn alters the function of several signaling molecules including NF-KB, AP-1, p53 and caspases. 21,36,37 When the system fails in 1 or more than 1 step, the possibility to have a mutated cell increases as a consequence of the high perturbation in the redox status that progresses, through ROI and RNI, into the nucleus.…”