Prostaglandin E2 reinforces the activation of Ras signal pathway in lung adenocarcinoma cells via EP3.

Prostaglandin E2 (PGE2)-dependent effects on various cell responses are regulated by respective PGE2 receptors (EP1, EP2, EP3, EP4) expressing in target cells. Alveolar type II cell (a main progenitor cell of lung adenocarcinoma) expressed only EP4, while human lung adenocarcinoma cells (A549) expressed EP3 as well as EP4. An antagonistic effect of EP3 against EP4 through the modulation of cyclic AMP level is required for PGE2-mediated activation of Ras signal pathway in A549 cells. These results suggest that the expression of EP3 may be a critical factor for the PGE2-mediated activation of Ras signal pathway in A549 cells.

alpha-Tocopheryloxybutyric acid enhances necrotic cell death in breast cancer cells treated with chemotherapy agent.

The overexpression of HER-2 receptor contributes to malignant transformation of breast cancer cells. We have reported that alpha-tocopheryloxybutyric acid (TE), non-antioxidative vitamin E ether derivative inhibits the activation of HER-2 receptor. The present study was undertaken to estimate if TE could act as a useful anti-cancer agent against a breast cancer cell overexpressing HER-2 receptor (MDA-MB-453 cell line) in combination with a conventional chemotherapy agent, adriamycin (ADR). TE enhanced cytotoxic effect of ADR against the human breast cancer cell at low doses less than IC(50). The enhancing effect was mainly dependent on the elevation of necrotic-like cell death but not apoptotic cell death. In conjugation with this event, the inactivation of HER-2 receptor in the breast cancer cell was caused by the combination of TE with ADR. These results suggest that TE enhances necrotic-like cell death in the breast cancer cells and that the cell death relates to the inactivation of HER-2 receptor in the breast cancer cells.

High oleic acid oil suppresses lung tumorigenesis in mice through the modulation of extracellular signal-regulated kinase cascade.

This study was undertaken to estimate the effect of dietary high oleic acid oil (OA) on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in mice. Diet containing 10% oil was fed to mice through experimental periods. On day 30 after NNK injection (100 mg/kg body weight, i.p.), the treatment increased the level of prostaglandin E2 (PGE2) as well as proliferating cell nuclear antigen, a marker of cell proliferation in a high linoleic acid oil (LA)-fed group but not in an OA-fed group. The NNK treatment also induced the activation of an extracellular signal-regulated kinase (Erk) cascade (Erk, Mek and Raf-1) in an LA-fed group. On the other hand, OA feeding abolished the NNK-induced activation of the Erk cascade. In conjugation with these events, OA feeding reduced lung tumor incidence and tumor multiplicity (percentage of mice with tumors) in mice compared with LA feeding at the 20th experimental week. These results suggest that OA suppresses lung tumorigenesis and that this suppression is correlated with the inhibition of PGE2 production and inactivation of the Erk cascade.

Effect of acerola cherry extract on cell proliferation and activation of ras signal pathway at the promotion stage of lung tumorigenesis in mice.

The present study was undertaken to estimate the effect of acerola cherry extract (ACE) pretreatment on cell proliferation and the activation of Ras signal pathway at a promotion stage of lung tumorigenesis in mice treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Pretreatment with ACE (dose, 70mg/kg body weight and 700 mg/kg body weight) inhibited increases in the levels of proliferating nuclear cell antigen and ornithine decarboxylase at the promotion stage. This treatment of ACE also suppressed the activation of Ras signal pathway at the same stage. These results suggest that ACE regulates abnormal cell growth at the promotion stage of lung tumorigenesis in mice treated with NNK as a result of suppression of the initiation stage.

Induction of cytotoxicity in human lung adenocarcinoma cells by 6-O-carboxypropyl-alpha-tocotrienol, a redox-silent derivative of alpha-tocotrienol.

Tocotrienols are one of the most potent anticancer agents of all natural compounds and the anticancer property may be related to the inactivation of Ras family molecules. The anticancer potential of tocotrienols, however, is weakened due to its short elimination half life in vivo. To overcome the disadvantage and reinforce the anticancer activity in tocotrienols, we synthesized a redox-silent analogue of alpha-tocotrienol (T3), 6-O-carboxypropyl-alpha-tocotrienol (T3E). We estimated the possibility of T3E as a new anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras gene. T3E showed cytotoxicity against A549 cells, a human lung adenocarcinoma cell line with a ras gene mutation, in a dose-dependent manner (0-40 microM), whereas T3 and a redox-silent analogue of alpha-tocopherol (T), 6-O-carboxypropyl-alpha-tocopherol (TE), showed much less cytotoxicity in cells within 40 microM. T3E cytotoxicity was based on the accumulation of cells in the G1-phase of the cell-cycle and the subsequent induction of apoptosis. Similar to this event, 24-hr treatment of A549 cells with 40 microM T3E caused the inhibition of Ras farnesylation, and a marked decrease in the levels of cyclin D required for G1/S progression in the cell-cycle and Bcl-xL, a key anti-apoptotic molecule. Moreover, the T3E-dependent inhibition of RhoA geranyl-geranylation is an inducing factor for the occurrence of apoptosis in A549 cells. Our results suggest that T3E suppresses Ras and RhoA prenylation, leading to negative growth control against A549 cells. In conclusion, a redox-silent analogue of T3, T3E may be a new candidate as an anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras genes.

Down-regulation of connexin 32 gene expression through DNA methylation in a human renal cell carcinoma cell.

BACKGROUND: We have recently reported that connexin (Cx) 32 is down-regulated in a human renal cell carcinoma (RCC) cell (Caki-2 cell). HYPOTHESIS: We postulated that the down-regulation of Cx32 gene in the RCC cell is due to hypermethylation of its promoter region. METHODS: We estimated methylation status in the promoter region of Cx32 gene in the RCC cell by DNA digestion with methylation-sensitive restriction enzyme and PCR, and methylation-specific PCR (MSP). We also checked the recovery of Cx32 gene expression in the RCC cell treated with a DNA methyltranferase inhibitor, 5-Aza-2'-deoxycytidine (5-Aza-CdR). RESULTS: Treatment with 5-Aza-CdR resulted in induction of Cx32 expression in the RCC cell. Hypermethylation of the Cx32 promoter region in the RCC cell was confirmed by DNA digestion with methylation-sensitive restriction enzyme and PCR, and MSP. CONCLUSION: We suggest that hypermethylation in the promoter region is a mechanism for the Cx32 gene repression in the RCC cell.

Genistein, a soy isoflavone, enhances necrotic-like cell death in a breast cancer cell treated with a chemotherapeutic agent.

Genistein is a major component of soybean isoflavone and has preventive effect against breast cancer. In breast cancer, the over-expression of HER-2 contributes to malignant transformation of the cancer cells. The present study was undertaken to estimate if genistein could act as a useful anti-cancer agent against a breast cancer cell overexpressing HER-2 in combination with a conventional chemotherapy agent, adriamycin (ADR). Genistein enhanced cytotoxic effect of ADR at low doses less than IC50 against the human breast cancer cell. The enhancing effect was mainly dependent on the elevation of necrotic-like cell death but not apoptotic cell death. In conjugation with this event, remarkable inactivation of HER-2 and Akt in the breast cancer cell was caused by the combination of genistein and ADR. These results suggest that genistein enhances necrotic-like cell death of the breast cancer cells through the inactivation of HER-2 receptor and Akt in combination with ADR.

Negative growth control of renal cell carcinoma cell by connexin 32: possible involvement of Her-2.

Connexin (Cx) genes have negative growth effects on tumor cells with certain cell specificity. We have previously reported that Cx32 is specifically downregulated in human renal cell carcinoma cell (RCC) lines as well as cancerous regions of kidneys and that the Cx is expressed in the progenitor cells of the carcinoma. However, the precise role of Cx32 in growth control of RCC cells remains unknown. In this study, we examined whether Cx32 could act in growth control against a human RCC cell, Caki-2 cell. In order to estimate the cell growth control, we established Caki-2 cells that have stable expression of Cx32 genes. Cx32 expression in Caki-2 cells induced contact inhibition of growth and reduced anchorage-independent growth ability, but did not significantly affect lag phase growth rates. This growth control by Cx32 was dependent on the inhibition of the cell-cycle transition from G1 to S phase at high cell density, and the inhibition of the cell-cycle transition related to the suppression of Her-2 activation. Furthermore, the suppression of Cx32 expression in Caki-2 cells by short interfering RNA induced the activation of Her-2. These data suggest that Cx32 has negative growth control of Caki-2 cells, partly due to the inhibition of the Her-2 activation.

Induction of apoptosis in a human breast cancer cell overexpressing ErbB-2 receptor by alpha-tocopheryloxybutyric acid.

The overexpression of ErbB-2 receptor relates to malignant transformation of breast cancer. The present study was carried out to establish the usefulness of alpha-tocopheryloxybutyric acid (TE) as a chemotherapeutic agent for human breast cancer. TE caused induction of apoptosis in MDA-MB-453 cells overexpressing the ErbB-2 receptor. TE reduced levels of activated ErbB-2 receptor and Akt. In contrast, TE induced the activation of p38, and SB203580, a specific inhibitor for p38, attenuated the TE-induced apoptosis. These data indicate that simultaneous occurrences of Akt inhibition and p38 activation by TE result in the cell death.