Hydrogen sulfide (H2S) is a gaseous bacterial metabolite that reaches high levels in the large intestine. In the present study, the effect of H2S on the proliferation of normal and cancerous colon epithelial cells was investigated. An immortalized colon epithelial cell line (YAMC) and a panel of colon cancer cell lines (HT-29, SW1116, HCT116) were exposed to H2S at concentrations similar to those found in the human colon. H2S inhibited normal and cancerous colon epithelial cell proliferation as measured by MTT assay. The anti-mitogenic effect of H2S was accompanied by G1-phase cell cycle arrest and the induction of the cyclin-dependent kinase inhibitor p21Cip. Moreover, exposure to H2S led to features characteristic of autophagy, including increased formation of LC3B+ autophagic vacuoles and acidic vesicular organelles as determined by immunofluorescence and acridine orange staining, respectively. Abolition of autophagy by RNA interference targeting Vps34 or Atg7 enhanced the anti-proliferative effect of H2S. Further mechanistic investigation revealed that H2S stimulated the phosphorylation of AMP-activated protein kinase (AMPK) and inhibited the phosphorylation of mammalian target of rapamycin (mTOR) and S6 kinase. Inhibition of AMPK significantly reversed H2S-induced autophagy and inhibition of cell proliferation. Collectively, we demonstrate that H2S inhibits colon epithelial cell proliferation and induces protective autophagy via the AMPK pathway.

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The use of nonsteroidal anti-inflammatory drugs is associated with a lower risk for esophageal squamous cell carcinoma, in which overexpression of cyclooxygenase-2 (COX-2) is frequently reported. Prostaglandin E 2 (PGE 2 ), a COX-2-derived eicosanoid, is implicated in the promotion of cancer growth. However, the precise role of PGE 2 in the disease development of esophageal squamous cell carcinoma remains elusive. In this study, we investigated the effect of PGE 2 on the proliferation of cultured esophageal squamous cell carcinoma cells (HKESC-1). Results showed that HKESC-1 cells expressed all four series of prostaglandin (EP) receptors, namely, EP1 to EP4 receptors. In this regard, PGE 2 and the EP2 receptor agonist (Ϯ)-15-deoxy-16S-hydroxy-17-cyclobutyl PGE 1 methyl ester (butaprost) markedly increased HKESC-1 cell proliferation. Moreover, the mitogenic effect of PGE 2 was significantly attenuated by RNA interference-mediated knockdown of the EP2 receptor, indicating that this receptor mediated the mitogenic effect of PGE 2 . In this connection, PGE 2 and butaprost induced phosphorylation of extracellular signal-regulated kinases 1/2 (Erk1/2), whose down-regulation by RNA interference significantly attenuated PGE 2 -induced cell proliferation. In addition, PGE 2 and butaprost increased c-Fos expression and activator protein 1 (AP-1) transcriptional activity, which were abolished by the mitogen-activated protein kinase/Erk kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)-butadiene ethanolate (U0126). AP-1-binding inhibitor curcumin also partially reversed the mitogenic effect of PGE 2 . Taken together, these data demonstrate for the first time that the EP2 receptor mediates the mitogenic effect of PGE 2 in esophageal squamous cell carcinoma via activation of the Erk/AP-1 pathway. This study supports the growth-promoting action of PGE 2 in esophageal squamous cell carcinoma and the potential application of EP2 receptor antagonists in the treatment of this disease.Esophageal cancer is a highly aggressive malignant disease with a 5-year survival rate of 10 to 15% (Jemal et al., 2003). There are two major histological types of esophageal cancer, squamous cell carcinoma and adenocarcinoma, each of which has distinct etiological and pathological characteristics. Although esophageal adenocarcinomas are more prevalent in the West, esophageal squamous cell carcinoma remains the predominant type worldwide (Souza, 2002). The etiology of esophageal squamous cell carcinoma is multifactorial, but cigarette smoking and alcohol consumption are Article, publication date, and citation information can be found at

Doxorubicin is a chemotherapeutic drug widely used for the treatment of advanced esophageal squamous cell carcinoma. However, its efficacy is usually limited by the development of multidrug resistance (MDR), which has been linked to the up-regulation of P-glycoprotein (P-gp) in cancer cells. Conventional nonsteroidal anti-inflammatory drugs and cyclooxygenase 2 (COX-2)-selective inhibitors have been demonstrated to overcome MDR in some cancer cells. Here we sought to elucidate the effect of COX inhibitors on doxorubicin-induced cytotoxicity in relation to P-gp function in human esophageal squamous cell carcinoma cells. Among the five tested COX inhibitors [indomethacin, 4-[5-(4-, nimesulide, and N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide (NS398)], all of which substantially suppressed prostaglandin E 2 (PGE 2 ) production to a similar extent, only the nonselective COX inhibitor indomethacin and the COX-2-selective inhibitor SC236 enhanced cytotoxic effects of doxorubicin on HKESC-1 and HKESC-2 cells. Moreover, these effects could not be reversed by the addition of PGE 2 . Knockdown of COX-2 by small interference RNA also failed to mimic the enhancing effects of indomethacin or SC236, implicating that their action is COX-and PGE 2 -independent. To this end, we observed that indomethacin and SC236 directly functioned as noncompetitive inhibitors of P-gp, which were manifested as a reduction of P-gp ATPase activity. Collectively, these findings suggest that the direct inhibitory effects of indomethacin and SC236 on P-gp may contribute to their ability to increase the intracellular retention of doxorubicin and thus enhance its cytotoxicity. The combination of indomethacin or SC236 with doxorubicin may have significant potential clinical application, especially in the circumvention of P-gp-mediated MDR in cancer cells.

Sung (2010) Macroautophagy and ERK phosphorylation counteract the anti-proliferative effect of proteasome inhibitor in gastric cancer cells, Autophagy, 6:2, 228-238,

Overexpression of cyclooxygenase-2 (COX-2) and elevation of its derivative prostaglandin E 2 (PGE 2 ) are implicated in human esophageal squamous cell carcinoma. The expression of c-Myc, an oncogenic transcription factor, is also upregulated in this malignant disease. This study sought to elucidate whether a functional connection exists between COX-2/PGE 2 and c-Myc in esophageal squamous cell carcinoma. Results showed that PGE 2 substantially increased the proliferation of cultured esophageal squamous cell carcinoma cells. In this regard, PGE 2 substantially increased the mRNA and protein expression of c-Myc and its association with the binding partner Max. Knockdown of c-Myc by RNA interference also significantly attenuated PGE 2 -induced cell proliferation. Further, mechanistic study revealed that PGE 2 increased the protein stability and nuclear accumulation of c-Myc via phosphorylation on serine 62 in an extracellular signal regulated kinase (ERK)-dependent manner. To this end, ERK activation by PGE 2 was completely abolished by protein kinase C (PKC) inhibitors. Moreover, the effect of PGE 2 on c-Myc expression was mimicked by EP2 receptor agonist. In addition, knockdown of EP2 receptor by EP2 siRNA attenuated PGE 2 -induced c-Myc expression. Collectively, our findings suggest that PGE 2 upregulates c-Myc via the EP2/PKC/ERK pathway. This study sheds new light on the carcinogenic mechanism of PGE 2 in esophageal squamous cell carcinoma. ' 2009 UICC