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Effective strategies for cancer prevention and treatment can be identified by understanding the mechanism of apoptotic pathways. In this study, we investigated the regulatory mechanism of quercetin-induced apoptosis through apoptosis signal-regulating kinase (ASK)-1 and mitogen-activated protein kinase pathways. Our results showed that quercetin increased apoptotic cell death through reactive oxygen species (ROS) generation and was responsible for ASK1 activation. Increasing ASK1 activity was accompanied by p38 activation. Interestingly, AMP-activated protein kinase (AMPK) seemed to be a critical controller of quercetin-regulated ASK1/p38 activation. Blocking AMPKalpha1 activity using Compound C, a synthetic inhibitor or siRNA showed that quercetin-activated ASK1 could not stimulate p38 activity. Thus, we suggested that quercetin-exerted apoptotic effects involve ROS/AMPKalpha1/ASK1/p38 signaling pathway, and AMPKalpha1 is a necessary element for apoptotic event induced by ASK1.

We isolated anthocyanins from fruits of Vitis coignetiae Pulliat, characterized the anthocyanin profile, and investigated the anti-invasive effects of the anthocyanins on human colon cancer cells. The anthocyanins inhibited cell invasion in a dose-dependent manner, as measured by Matrigel invasion assays, by suppression of matrix metalloproteinase (MMP)-2 and MMP-9 expression. The anti-invasive activity of the anthocyanins was associated with modulation of constitutive nuclear factor kappaB (NF-kappaB) activation. The activation of NF-kappaB triggered by tumor necrosis factor-alpha was also inhibited by the anthocyanins through suppression IkappaBalpha phosphorylation. AIMs inhibited the expression of NF-kappaB-regulated proteins. In conclusion, this study suggested that the anthocyanins isolated from fruits of V. coignetiae Pulliat should have anti-invasive activities on human colon cancer cells and the activities should be related to the inhibition of NF-kappaB-regulated proteins such as MMP-2 and MMP-9 expression through the inhibition of NF-kappaB activation.

The topical application of TPA (12-O-tetradecanoylphorbol-13-acetate) to animal skin or direct treatment of TPA to cell cultures leads to inflammatory responses by enhancing cyclooxygenase 2 (COX-2) expression, and specific COX-2 inhibitors counteract this kind of inflammatory response. Furthermore, suppression of these inflammatory events by dietary-origin chemopreventive agents can provide a potential strategy to control carcinogenesis. In this in vivo study, the mammary glands of mature female rats were treated with TPA, and then the effects of genistein alone or in combination with capsaicin on suppression of inflammatory responses were examined. The combined effects of genistein and capsaicin on COX-2, pJNK, pERK, and pp38 expressions were additive or nonadditive, depending on signals tested. In vitro MCF-7 breast cancer cells, the apoptotic bodies as shown with Hoechst 33342 dye, exhibited a synergistic effect between genistein and capsaicin. The abilities of genistein alone or in combination with capsaicin in inhibiting breast cancer cell proliferation through the modulation of AMPK and COX-2 were tested. AMPK activation by genistein in combination with capsaicin is critical for inhibiting COX-2. We propose that genistein in combination with capsaicin exerts anti-inflammatory and anticarcinogenic properties through the modulation of AMPK and COX-2 and possibly various mitogen-activated protein kinases synergistically or nonsynergistically.

Maternal chorioamnionitis has been associated with abnormal lung development. We examined the effect of maternal chorioamnionitis on the expression of transforming growth factor-beta1 (TGF-beta1) in the lungs of preterm infants. A total of 63 preterm (or=34 weeks) infants who were intubated in the delivery room were prospectively enrolled. Their placentas were examined for the presence of chorioamnionitis. Bronchoalveolar lavage (BAL) fluid and cells were obtained shortly after birth. TGF-beta1 was measured in BAL fluid and TGF-beta1 mRNA expression was determined by reverse transcription polymerase chain reaction (RT-PCR) in BAL cells. TGF-beta1 mRNA expression in BAL cells showed a positive correlation with gestational age (r=0.414, p=0.002). TGF-beta1 mRNA expression was significantly decreased in the presence of maternal chorioamnionitis (0.70+/-0.12 vs. 0.81+/-0.15, p=0.007). Adjustment for gestational age, birth weight, and delivery mode did not nullify the significance. TGF-beta1 mRNA expression was marginally significantly decreased in preterm infants who developed bronchopulmonary dysplasia (BPD) later (0.75+/-0.11 vs. 0.82+/-0.15, p=0.055). However, adjustment for gestational age, patent ductus arteriosus (PDA), and maternal chorioamnionitis nullified the significance. These results might be an indirect evidence that maternal chorioamnionitis may inhibit normal lung development of fetus.

Selenium has received much attention as an anticancer agent, although the mechanisms of action underlying its pro-apoptotic properties remain unclear. Tumors that respond well to antioxidant treatments, such as hepatocellular carcinoma (HCC), may benefit from treatment with selenium as this compound also has antioxidant properties. Furthermore, a major oncogenic driver in HCC is the nuclear transcription co-activator, β-catenin. In the present study, we examined the mechanism by which selenium reduces survival of HCC cells, and whether this was associated with modulation of the β-catenin pathway. Hep3B cell lines and cancer cell xenografted animals were treated with selenium, and apoptotic events or signals such as AMPK, β-catenin and GSK3β were determined. Further interactions among β-catenin, glycogen synthase kinase 3β (GSK3β), and AMPK were explored by applying AMPK small interfering RNA (siRNA) or GSK3β siRNA with western blotting or immunofluorescence microscopic observation. Selenium activated AMPK, which in turn suppressed β-catenin. Selenium induced the translocation of AMPK into the nucleus and prevented the accumulation of β-catenin therein. Upon inactivation of AMPK by AMPK siRNA, selenium no longer modulated β-catenin, implying that AMPK is an upstream signal for β-catenin. We found that the binding between AMPK and β-catenin occurs in the cytosolic fraction, and therefore concluded that the cancer cell antiproliferative effects of selenium are mediated by a GSK3β-independent AMPK/β-catenin pathway, although AMPK-mediated GSK3β regulation was also observed. We primarily discovered that AMPK is a crucial regulator initiating selenium-induced inhibition of β-catenin expression. Taken together, these novel findings help to illuminate the molecular mechanisms underlying the anticancer effect of selenium and highlight the regulation of β-catenin by selenium.

Luteolin, a plant-derived flavonoid, is thought to inhibit tumor growth. However, the precise molecular mechanisms by which luteolin inhibits cancer cell growth remain unclear. In the present study, we evaluated the role of AMP-activated protein kinase (AMPK) in the inhibition of cancer cell growth by luteolin in HepG2 hepatocarcinoma cells. AMPK is a metabolic sensor and may prevent carcinogenesis via modulation of signaling networks. We found that luteolin strongly induced cell death in HepG2 cells and dramatically reduced the tumor volume in a tumor xenograft model; both effects were accompanied by AMPK activation by luteolin. Luteolin also had a strong inhibitory effect on nuclear factor (NF)-κB. To determine the relationship between AMPK and NF-κB signaling, we used Compound C, a pharmacological AMPK inhibitor, and a dominant-negative form of AMPK. Our results indicated that inhibition of AMPK activity restored luteolin-inhibited NF-κB DNA-binding activity. These results suggest that AMPK activity is critical for the inhibition of cancer cell growth, possibly via modulation of NF-κB activity. We also showed that luteolin treatment causes the release of reactive oxygen species (ROS) and that these intracellular ROS in turn mediate AMPK-NF-κB signaling in HepG2 hepatocarcinoma cells. In conclusion, we propose that AMPK is a novel regulator of NF-κB in luteolin-induced cancer cell death. Furthermore, our results suggest that AMPK is an attractive target for cancer prevention by flavonoids.

AMP-activated protein kinase (AMPK) has emerged as a therapeutic target of cancer. AMPK functions as an upstream regulator of proliferative signals such as mammalian target of rapamycin (mTOR), tuberous sclerosis complex (TSC), p70S6 and elongation factor-2, indicating that AMPK can be applied for the inhibition of cancer cell proliferation via modulating the proliferative signaling network. The Akt/mTOR signaling pathway is activated in colon cancer. The well known mTOR inhibitor rapamycin has a disadvantage of feedback stimulation of Akt. Anthocyanins are naturally-occurring mTOR inhibitor possessing Akt inhibitory activities. We have investigated the mTOR inhibitory effect of anthocyanins through the activation of AMPK. In this study, anthocyanins were applied to colon cancer cells and tumor-bearing xenograft models to investigate their anti-proliferative and pro-apoptotic effects, and elucidate the mechanisms that link AMP-activated protein kinase (AMPK) α1 activation to the survival signal of mTOR. Our results indicated that anthocyanins significantly decreased phospho-mTOR comparable to rapamycin, a synthetic mTOR inhibitor, and this inhibitory effect of anthocyanins on mTOR was completely abrogated by inactivating AMPKα1. Furthermore, suppression of cell growth with anthocyanins was also alleviated in the absence of noticeable AMPKα1 activities. For the first time we have found anthocyanins as novel AMPKα1 activators, and in conditions of AMPKα1 inactivation, anthocyanins lost their ability to inhibit mTOR in HT-29 colon cancer cells. The activation of AMPKα1, and the deactivation of mTOR and Akt were observed in anthocyanins-treated tumor-bearing xenograft models. The results from this study suggest that there is a complex interaction between AMPKα1 and mTOR signaling, and anthocyanins are powerful AMPKα1 activators that inhibit cancer cell growth by inhibiting mTOR phosphorylation.

In lieu of elucidating bidirectional connecting mechanism between AMP-activated protein kinase (AMPK) and survival signal Akt we applied MCF-7 breast cancer cells to determine whether AMPK modulation alters Akt signals and vice versa. Suppression of Akt activities with a synthetic Akt inhibitor alleviated AMPK activities suggesting that Akt is capable of inhibiting AMPK. Also the activation of AMPK with quercetin strongly abrogated Akt activities. Treating cancer cells with AMPK siRNA or Compound C resulted in marked increment of Akt dephosphorylation indicating that AMPK has antagonistic activities towards Akt. However, quercetin exerted Akt inhibitory activities in the absence of AMPK activation. Quercetin induced partial co-localization of phospho-Akt and phospho-AMPK in the nucleus even though their interaction seems to be indirect since the immunoprecipitation data indicate there was no direct binding between total Akt and AMPK. These results suggest there is a mutual suppressive interaction between AMPK and Akt. The investigation of mutual suppression between Akt and AMPK by chemo-preventive agents such as quercetin may provide a mechanistic rational for controlling breast tumor cell growth.

Activation of the mammalian target of rapamycin (mTOR) pathway promotes tumorigenesis, and inhibiting the mammalian target of rapamycin complex 1 (mTORC1) has emerged as an attractive target for suppressing tumor growth. We found that selenium treatment of HT-29 colon cancer cells suppressed mTORC1 through Akt-independent and -dependent pathways. In Akt-independent mTORC1 inhibition in selenium-treated colon cancer cells, adenosine monophosphate-activated protein kinase (AMPK) alpha(1) was crucial for suppression of mTORC1 activity. In contrast, the Akt-dependent mTORC1 inhibition by selenium did not require AMPKalpha(1). The importance of the AMPKalpha(1)-mTORC1 pathway in mediating the antiproliferative action of selenium was examined in xenograft tumors, and the suppression of mTORC1 as well as Akt was concomitant with an increase in AMPKalpha(1) activity. These findings suggest that the antiproliferative effect of selenium is mediated by an Akt-independent AMPKalpha(1)/mTORC1 pathway or by the Akt/tuberous sclerosis complex 2 /mTORC1 pathway.

AMP-activated protein kinase (AMPK), a highly conserved protein in eukaryotes, functions as a major metabolic switch to maintain energy homeostasis. It also intrinsically regulates the mammalian cell cycle. Moreover, the AMPK cascade has emerged as an important pathway implicated in cancer control. In this study we investigated the effects of curcumin on apoptosis and the regulatory effect of the AMPK-cyclooxygenase-2 (COX-2) pathway in curcumin-induced apoptosis. Curcumin has shown promise as a chemopreventive agent because of its in vivo regression of various animal-model colon cancers. This study focused on exploiting curcumin to apply antitumorigenic effects through modulation of the AMPK-COX-2 cascade. Curcumin exhibited a potent apoptotic effect on HT-29 colon cancer cells at concentrations of 50 micromol/L and above. These apoptotic effects were correlated with the decrease in pAkt and COX-2, as well as the increase in p-AMPK. Cell cycle analysis showed that curcumin induced G(1)-phase arrest. Further study with AMPK synthetic inhibitor Compound C has shown that increased concentrations of Compound C would abolish AMPK expression, accompanied by a marked increase in COX-2 as well as pAkt expression in curcumin-treated HT-29 cells. By inhibiting AMPK with Compound C, we found that curcumin-treated colon cancer cells were no longer undergoing apoptosis; rather, they were proliferative. These results indicate that AMPK is crucial in apoptosis induced by curcumin and further that the pAkt-AMPK-COX-2 cascade or AMPK-pAkt-COX-2 pathway is important in cell proliferation and apoptosis in colon cancer cells.

This study investigated the apoptotic regulation by green tea catechin epigallcatechin-3-gallate (EGCG) on colon cancer cells in the presence of low-dose H(2)O(2) known to exert the activation of signal pathways leading to cell proliferation. In the presence of low-dose H(2)O(2), EGCG induced apoptosis and abolished the cell-proliferative effect exhibited by low-dose H(2)O(2). This reduction of growth was accompanied by an activation of AMP-activated kinase (AMPK), a decrease in cyclooxygenase-2 (COX-2) expression and prostaglandin E(2) (PGE(2)) levels, and the induction of apoptotic markers such as p53 and poly(ADP-ribose) polymerase (PARP) cleavage. The low-dose H(2)O(2) stimulated COX-2 expression, and treating cells with synthetic AMPK activator AICAR (5-aminoimiazole-4-carboxamide-1-beta-d-ribofuranoside) resulted in greater suppression of COX-2 expression and PGE(2). By treating cells with high concentrations of the reactive oxygen species (ROS) scavenger NAC (N-acetyl-1-cysteine), the apoptotic effect of EGCG was abolished and led to suppression of AMPK and COX-2, indicating that the liberation of excessive ROS might be the upstream signal of the AMPK-COX-2 signaling pathway even in the presence of low-dose H(2)O(2).

In this study, we investigated the molecular basis of Korean kidney bean husk extract, with emphasis on its ability to control intracellular signaling cascades of AMP-activated protein kinase (AMPK) responsible for inducing antitumor activities in colon cancer cells. Recently, the evolutionarily conserved serine/threonine kinase, AMPK, has emerged as a possible target molecule of tumor control. We investigated the effects of Korean kidney bean husk extract on apoptosis regulation and the activation of AMPK. Korean kidney bean husk extract exhibited a series of antitumor effects such as cell death and apoptotic body appearance. These antitumor potentials were accompanied by the increase in p-AMPK and p-Acc as well as antitumor proteins p53 and p21. The stimulation of AMPK by this extract was blocked with the synthetic AMPK inhibitor Compound C at 10 micromol/L, and the combined treatment of Compound C and the AMPK activator AICAR (5-aminoimiazole-4-carboxamide-1-beta-D-ribofuranoside) showed that Compound C could inhibit the activation of AMPK at the concentration of 20 micromol/L. In conclusion, the ability of carcinogenesis control by Korean kidney bean husk extract with high potency suggests its value as an antitumor agent in colon cancer therapy.

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is activated during ATP-depleting metabolic states, such as hypoxia, heat shock, oxidative stress, and exercise. As a highly conserved heterotrimeric kinase that functions as a major metabolic switch to maintain energy homeostasis, AMPK has been shown to exert as an intrinsic regulator of mammalian cell cycle. Moreover, AMPK cascade has emerged as an important pathway implicated in cancer control. In this article, we have investigated the effects of capsaicin on apoptosis in relation to AMPK activation in colon cancer cell. Capsaicin-induced apoptosis was revealed by the presence of nucleobodies in the capsaicin-treated HT-29 colon cancer cells. Concomitantly, the activation of AMPK and the increased expression of the inactive form of acetyl-CoA carboxylase (ACC) were detected in capsaicin-treated colon cancer cells. We showed that both capsaicin and 5'-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR), an AMPK activator possess the AMPK-activating capacity as well as apoptosis-inducing properties. Evidence of the association between AMPK activation and the increased apoptosis in HT-29 colon cancer cells by capsaicin treatment, and further findings of the correlation of the activated AMPK and the elevated apoptosis by cotreatment of AICAR and capsaicin support AMPK as an important component of apoptosis, as well as a possible target of cancer control.

AMPK (AMP-activated protein kinase) is highly conserved in eukaryotes, where it functions primarily as a sensor of cellular energy status. Recent studies indicate that AMPK activation strongly suppresses cell proliferation in non-malignant cells as well as in tumor cells. In this study, quercetin activated AMPK in MCF breast cancer cell lines and HT-29 colon cancer cells, and this activation of AMPK seemed to be closely related to a decrease in COX-2 expression. The application of a COX-2 inhibitor or cox-2-/- cells supported the idea that AMPK is an upstream signal of COX-2, and is required for the anti-proliferatory and pro-apoptotic effects of quercetin. The suppressive or growth inhibitory effects of quercetin on COX-2 were abolished by treating cancer cells with an AMPK inhibitor Compound C. These results suggest that AMPK is crucial to the anti-cancer effect of quercetin and that the AMPK-COX-2 signaling pathway is important in quercetin-mediated cancer control.

BackgroundActivation of the Wnt pathway is known to promote tumorigenesis and tumor metastasis, and targeting Wnt pathway inhibition has emerged as an attractive approach for controlling tumor invasion and metastasis. The major pathway for inhibiting Wnt is through the degradation of β-catenin by the GSK3-beta/CK1/Axin/APC complex. It was found that Hep3B hepato-carcinoma cells respond to anthocyanins through GSK3-beta-induced suppression of beta-catenin; however, they cannot dephosphorylate GSK3-beta without AMPK activation.MethodsWe tested the effects of anthocyanins on proliferation and apoptosis by MTT and Annexin V-PI stainingin vitro. Mouse xenograft models of hepato-carcinomas were established by inoculation with Hep3B cells, and mice were injected with 50 mg/kg/ml of anthocyanins. In addition, protein levels of p-GSK3-beta, beta-catenin, p-AMPK, MMP-9, VEGF, and Ang-1 were also analyzed using western blot.ResultsAnthocyanins decrease phospho-GSK3-beta and beta-catenin expression in anin vivotumor xenograft model, increase AMPK activity in this model, and inhibit cell migration and invasion, possibly by inhibiting MMP-2 (in vitro) and the panendothelial marker, CD31 (in vivo). To elucidate the role of the GSK3-beta/beta-catenin pathway in cancer control, we conditionally inactivated this pathway, using activated AMPK for inhibition. Further, we showed that AMPK siRNA treatment abrogated the ability of anthocyanins to control cell proliferation and metastatic potential, and Compound C, an AMPK inhibitor, could not restore GSK3-beta regulation, as exhibited by anthocyanins in Hep3B cells.ConclusionThese observations imply that the AMPK-mediated GSK3-beta/beta-catenin circuit plays crucial roles in inhibiting cancer cell proliferation and metastasis in anthocyanin-treated hepato-carcinoma cells of Meoru origin.