Cancer cells acquire drug resistance as a result of selection pressure dictated by unfavorable microenvironments. This survival process is facilitated through efficient control of oxidative stress originating from mitochondria that typically initiates programmed cell death. We show this critical adaptive response in cancer cells to be linked to uncoupling protein-2 (UCP2), a mitochondrial suppressor of reactive oxygen species (ROS). UCP2 is present in drug-resistant lines of various cancer cells and in human colon cancer. Overexpression of UCP2 in HCT116 human colon cancer cells inhibits ROS accumulation and apoptosis after exposure to chemotherapeutic agents. Tumor xenografts of UCP2-overexpressing HCT116 cells retain growth in nude mice receiving chemotherapy. Augmented cancer cell survival is accompanied by altered NH 2 -terminal phosphorylation of the pivotal tumor suppressor p53 and induction of the glycolytic phenotype (Warburg effect). These findings link UCP2 with molecular mechanisms of chemoresistance. Targeting UCP2 may be considered a novel treatment strategy for cancer. [Cancer Res 2008;68(8):2813-9]

Background & Aims p53 and its transcriptional target miRNA34a have been implicated in the pathogenesis of fatty liver. We tested the efficacy of a p53 inhibitor, pifithrin-α p-nitro (PFT) in attenuating steatosis, associated oxidative stress and apoptosis in a murine model of non-alcoholic fatty liver disease (NAFLD). Methods C75Bl/6J mice were fed a high-fat (HFD) or control diet for 8 weeks, PFT or DMSO (vehicle) were administered three times per week. Markers of oxidative stress and apoptosis as well as mediators of hepatic fatty acid metabolism were assessed by immunohistochemistry, Western-blot, real-time PCR and biochemical assays. Results PFT administration suppressed HFD-induced weight gain, ALT elevation, steatosis, oxidative stress and apoptosis. PFT treatment blunted the HFD-induced upregulation of miRNA34a and increased SIRT1 expression. In the livers of HFD-fed, PFT-treated mice activation of the SIRT1/PGC1α/PPARα axis increased the expression of malonyl-CoA decarboxylase (MLYCD), an enzyme responsible for malonyl-CoA (mCoA) degradation. Additionally, the SIRT1/LKB1/AMPK pathway (upstream activator of MLYCD) was promoted by PFT. Thus, induction of these two pathways by PFT diminished the hepatic mCoA content by enhancing MLYCD expression and function. Since mCoA inhibits carnitine palmitoyltransferase 1 (CPT1), the decrease of hepatic mCoA in the PFT-treated, HFD-fed mice increased CPT1 activity, favored fatty acid oxidation and decreased steatosis. Additionally, we also demonstrated that PFT abrogated steatosis and promoted MLYCD expression in palmitoleic acid- treated human HepaRG cells. Conclusions The p53 inhibitor PFT diminished hepatic triglyceride accumulation and lipotoxicity in mice fed a HFD by depleting mCoA and favoring the β-oxidation of fatty acids.

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Chronic ethanol consumption in the Long-Evans (LE) rat has been associated with hepatic p53 activation, and inhibition of the insulin/PI3K/AKT signal transduction cascade due to increased expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). We hypothesize that p53 activation and altered insulin signaling may influence the susceptibility of rats to ethanol-induced liver damage. Furthermore, p53 not only activates programmed cell death pathways and suppresses hepatocellular survival signals, but promotes gluconeogenesis to increase systemic insulin resistance due to a novel metabolic function. Here, we present evidence that chronic ethanol feeding in Fischer (F), Sprague-Dawley (SD) and LE rats promotes p53 activation, hepatic steatosis, oxidative stress, p53 up-regulated modulator of apoptosis (PUMA) and PTEN expression, which contribute to hepatocellular death and diminished insulin signaling in the liver. Such changes are pronounced in the LE, less prominent in SD, and virtually absent in the F rat strain. More importantly, there is activation of Tp53-induced glycolysis and apoptosis regulator (TIGAR) in the ethanol-fed LE rat. This event generates low hepatic fructose-2, 6-bisphosphate (Fru-2,6-P 2 ) levels, reduced lactate/pyruvate ratio and may contribute to increased basal glucose turnover and high residual hepatic glucose production during euglycemic hyperinsulinemic clamp. Conclusions: p53 activation correlates with the susceptibility to ethanol-induced liver damage in different rat strains. p53 not only orchestrates apoptosis and suppresses cell survival, but by activating TIGAR and decreasing hepatic Fru-2,6-P 2 levels it may also promote insulin resistance and therefore, contribute to the metabolic abnormalities associated with hepatic steatosis.

The control of liver regeneration remains elusive. Because reactive oxygen species (ROS) are able to mediate cell growth arrest and activate proteins that inhibit the cell cycle, ROS production may have a negative impact on liver regeneration. We examined how liver regeneration is affected by uncoupling protein-2 (UCP2), an inner mitochondrial membrane carrier that senses and negatively regulates superoxide production. Liver regeneration was monitored up to 5 days and was found to be significantly delayed in UCP2 ؊/؊ mice after partial hepatectomy. Apoptosis rates in UCP2 ؉/؉ and UCP2 ؊ /؊ liver remnants were similar, while parameters of cell proliferation indicated a diminished response in UCP2 ؊ /؊ mice with corresponding changes in the expression of key cell cycle regulatory proteins and prolonged activation of stress-responsive protein kinase p38. Levels of malondialdehyde, a marker of ROS generation and oxidant stress, were elevated in UCP2 ؊ /؊ livers at every examined time point. Liver remnants of UCP2 ؉ /؉ mice 48 hours post-hepatectomy showed a fourfold increase in the expression of UCP2 protein primarily detected in hepatocytes. In conclusion, our results suggest that absent or insufficient UCP2 function in the regenerating liver results in increased ROS production and negatively modulates the control of cell cycle.

We present the development of a new imaging technique for the early diagnosis of hepatocellular carcinoma that utilizes surface-modified gold nanoparticles in combination with x-ray imaging. Tissues labeled with these electron-dense particles show enhanced x-ray scattering over normal tissues, distinguishing cells containing gold nanoparticles from cells without gold in x-ray scatter images. Our results suggest that this novel approach could enable the in vivo detection of tumors as small as a few millimeters in size.

Recent findings link metabolic transformation of cancer cells to aberrant functions of mitochondrial uncoupling proteins (UCPs). By inducing proton leak, UCPs interfere with mitochondrial synthesis of adenosine 5′-triphosphate, which is also a key determinant of glycolytic pathways. In addition, UCP suppress the generation of superoxide, a byproduct of mitochondrial electron transport and a major source of oxidative stress. The near ubiquitous UCP2 becomes highly abundant in some cancers and may advance metabolic reprogramming, further disrupt tumour suppression, and promote chemoresistance. Here we review current evidence to suggest that inhibition of mitochondrial uncoupling may eliminate these responses and reveal novel anti-cancer strategies.

Background Chronic ethanol consumption impairs the ability of insulin to suppress hepatic glucose production in a strain-dependent manner, with hepatic insulin resistance being greater in Long-Evans (LE) than Sprague-Dawley (SD) rats. We assessed whether strain differences exist for whole-body and tissue glucose uptake under basal and insulin-stimulated conditions and whether they were associated with coordinate strain-dependent elevations in muscle cytokines. Methods Male rats (160 g) were provided the Lieber-DeCarli ethanol-containing (36% total energy) diet or pair-fed a control diet for 8 weeks. Rats were studied in the basal state or during a euglycemic hyperinsulinemic clamp, and whole-body glucose flux assessed using 3H-glucose and in vivo tissue glucose uptake by 14C-2-deoxyglucose. Results Ethanol impaired whole-body insulin-mediated glucose uptake (IMGU) more in SD than LE rats. This difference was due to impaired IMGU by gastrocnemius and heart in ethanol-fed SD vs LE rats. However, decreased IMGU in adipose tissue (epididymal and perirenal) produced by ethanol was comparable between strains. Ethanol-induced insulin resistance in muscle from SD rats was associated with reduced AKT and AS160 phosphorylation and plasma membrane-localized GLUT4 protein as well as enhanced phosphorylation of JNK and IRS-1 (S307), changes which were absent in muscle from LE rats. Ethanol increased TNFα mRNA in gastrocnemius and fat under basal conditions in both SD and LE rats; however, hyperinsulinemia decreased TNFα in skeletal muscle from LE but not SD rats. IL-6 mRNA in gastrocnemius was increased under basal conditions and increased further in response to insulin in SD rats, but no ethanol- or insulin-induced change was detected in muscle IL-6 of LE rats. Conclusion These data indicate strain-dependent differences in ethanol-induced IMGU in skeletal and cardiac muscle, but not fat, associated with sustained increases in TNFα and IL-6 mRNA and JNK activation, and decreased plasma membrane GLUT4 in response to insulin.