Colon cancer and apoptosis

Estudo da expressão citofotométrica do marcador tumoral Caspase-3 no adenocarcinoma de cólon

RACIONAL: O adenocarcinoma de cólon é a segunda causa mais comum de morte por câncer em homens e mulheres, sendo responsável por mais de cinco milhões de mortes por ano. No momento do diagnóstico apenas 70% dos tumores são ressecáveis, 75% são curáveis e 25% poderão ter recorrência da doença. A apoptose é uma das responsáveis pelo equilíbrio homeostático entre as células. Durante o desenvolvimento do processo de degeneração maligna celular o desequilíbrio na apoptose é considerado um dos principais marcos neoplásicos. A caspase-3 é uma das mais importantes moléculas na apoptose, sendo sua efetora principal. Sua expressão e prognóstico têm sido relatados em vários estudos e revisões com seu papel valorizado desde o surgimento do pólipo até a sua transformação maligna, com a taxa de apoptose diminuindo progressivamente. OBJETIVOS: Avaliar a expressão citofotométrica computadorizada do marcador Caspase-3 no adenocarcinoma de cólon; avaliá-lo nas fases evolutivas na classificação modificada de Dukes e comparar sua expressão nos tumores do lado direito e esquerdo do cólon. MÉTODOS: Utilizaram-se 19 casos de câncer recuperados de blocos de parafina confirmados por hematoxilina-eosina e submetidos à técnica imunoistoquímica da estreptavidina-biotina com anticorpo policlonal anti-caspase-3. Após este processo as lâminas marcadas foram submetidas à leitura pelo sistema SAMBA com o software IMUNNO 4.00. Foram analisados três índices: marcagem (Label index), heterogeneidade e densidade óptica. Utilizaram-se a marcagem individual, avaliação da expressão do marcador e grupos definidos de tumores com classificação Dukes e pelo lado do tumor. RESULTADOS: A média do índice de marcagem da caspase-3 foi de 85,24 e da densidade óptica de 39,55. Na classificação Dukes de 12 tipos B tiveram índice de marcagem de 86,20 e a densidade óptica de 37,72 e para os 7 tipos C a área de marcagem foi de 85,66 e a densidade óptica foi de 42,71 não sendo possível identificar diferença em relação a classificação de Dukes. Quanto ao lado do tumor os 11 tumores à esquerda tiveram índice de marcagem de 86,65 e densidade óptica de 43,29 e os 8 à direita tíndice de marcagem de 83,29 e densidade óptica de 39,44 não sendo possível observar diferença estatística significante. CONCLUSÕES: A caspase-3 possui alta expressão individual revelando-se marcador de boa utilidade no estudo do adenocarcinoma de cólon e da fase pró-apoptóica da sua tumorigênese pelo seu alto grau de índice de marcagem e densidade óptica. Em relação à classificação Dukes não houve diferença entre os tipos B e C, como também em relação ao lado direito e esquerdo do cólon.

Modification of Gene Products Involved in Resistance to Apoptosis in Metastatic Colon Cancer Cells: Roles of Fas, Apaf-1, NFκB, IAPs, Smac/DIABLO, and AIF

BACKGROUND

Colon cancer becomes resistant to apoptosis as it acquires metastatic potential. SW480 and SW620 colon cancer cells were established from the same patient at different stages of tumor progression. The stage III colorectal cancer cell line (SW620) is more resistant to apoptosis. In the present report, we investigated the apoptotic gene products that might account for colon cancer evasion of immune attack and chemoradioresistance-induced apoptosis.

METHODS

SW480 and SW620 cells were used for this experiment. Type 1 apoptosis was induced by CH-11. Type 2 apoptosis was induced by cisplatin and ionizing radiation. Apoptosis was determined by caspase-3 activity and terminal deoxynucleotidyl transferase mediated dUTP nick end labeling. Gene products Fas, TRAIL, c-FLIP, Bid, BAX, Bcl-2, Bcl-xL, Apaf-1, nuclear factor-kappa B, Smac/DIABLO, apoptosis inducing factor, and the inhibitors of apoptosis were investigated by immunocytochemistry and Western blot analyses.

RESULTS

SW620 cell lines were more resistant to both Type 1 and Type 2 apoptosis induced by CH-11, cisplatin, and ionizing radiation, respectively. Examination of the extrinsic pathway demonstrated Fas receptor to be down-regulated in SW620. Apaf-1 was decreased in SW620 cells; while other members of the mitochondrial pathway including Bax, Bid, Bcl-xL, and Bcl-2 demonstrated minimal alterations of protein levels in both cell lines. Survivin and XIAP protein levels were increased in SW620 cells, which correlated with nuclear expression of nuclear factor-kappa B in SW620 cells but not SW480. Mitochondrial-released factors including Smac/DIABLO and apoptosis inducing factor were increased in SW480 cells.

CONCLUSIONS

SW620 cells have acquired genetic defects both in the intrinsic and extrinsic pathways of apoptosis, which may explain in part the ability of colon cancer cells to escape the immune system and to become chemoradioresistant. These genes may be potential targets for chemoradiosensitization in advanced colorectal cancer.

Celecoxib induces apoptosis by inhibiting the expression of survivin in HeLa cells

The effect of celecoxib, a cyclooxygenase-2 selective inhibitor, on a human cervical cancer cell line, HeLa cells, was examined. We found that celecoxib increased DNA ladder formation and the activity of caspase-3, indicating that celecoxib induced apoptosis in HeLa cells. Celecoxib suppressed the expression of an anti-apoptotic protein, survivin, in both protein and mRNA levels. The overexpression of survivin overrode caspase-3 activation induced by celecoxib. Subsequently, we performed luciferase reporter assay with the reporter vector containing human survivin promoter region and electrophoretic mobility shift assay and found that the -75 to -66 bp region relative to the initiating codon played an important role in celecoxib action to suppress survivin promoter activity. Our findings might provide a new insight into the anti-cancer effects of celecoxib.

The suppression of aberrant crypt multiplicity in colonic tissue of 1,2-dimethylhydrazine-treated C57BL/6J mice by dietary flavone is associated with an increased expression of Krebs cycle enzymes

Colorectal cancer is the second leading cause of cancer deaths worldwide with diet playing a prominent role in disease initiation and progression. Flavonoids are secondary plant compounds that are suggested as protective ingredients of a diet rich in fruits and vegetables. We here tested whether flavone, a flavonoid that proved to be an effective apoptosis inducer in colon cancer cells in culture, can affect the development of aberrant crypt foci (ACFs) in C57BL/6J mice in vivo when preneoplastic lesions were induced by the carcinogen 1,2-dimethylhydrazine (DMH). Flavone applied at either a low dose (15 mg/kg body wt per day) or a high dose (400 mg/kg body wt per day) reduced the numbers of ACFs significantly, independent of whether it was supplied simultaneously with the carcinogen (blocking group) or subsequent to the tumor induction phase (suppressing group). Proteome analysis performed in colonic tissue samples revealed that flavone treatment increased the expression of a number of Krebs cycle enzymes in the suppressing group and this was associated with reduced crypt multiplicity. It suggests that mitochondrial substrate oxidation is increased by flavone in colonic cells in vivo as already observed in HT-29 cells in vitro as the prime mechanism underlying tumor cell apoptosis induction by flavone. In conclusion, flavone reduces the number of ACFs in DMH-treated mice at doses that can be achieved for flavonoids by a diet rich in fruits and vegetables. Moreover, reduction in crypt multiplicity by flavone is most probably due to the preservation of a normal oxidative metabolism.

Celecoxib inhibits the expression of survivin via the suppression of promoter activity in human colon cancer cells

We investigated the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on human colon cancer cell lines to clarify the mechanisms underlying the chemopreventive effect of NSAIDs. Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, induced apoptosis and strongly reduced the expression of an anti-apoptotic protein, survivin, in both protein and mRNA levels in HCT-116 cells. Subsequently, we conducted luciferase reporter assay using a reporter gene driven by the human survivin promoter. A series of analyses using luciferase reporter constructs containing fragments of the survivin promoter and electrophoretic mobility shift assay indicated that the -75/-66 bp region relative to the initiating codon was involved in celecoxib action to suppress survivin promoter activity. Celecoxib also suppressed the activity of TOPflash, T-cell factor reporter plasmid, and the reporter gene driven by the human cyclin D1 promoter, suggesting that this compound inhibited the expression of Wnt/beta-catenin signaling target genes. Further, we found that other NSAIDs including indomethacin, resveratrol, and SC-560 induced apoptosis and suppressed the expression of survivin and the Wnt/beta-catenin signaling pathway in HCT-116 cells, indicating that these effects were likely to be common among NSAIDs. Moreover, NSAIDs (celecoxib, SC-560 and indomethacin) also suppressed the expression of cyclin D1 and survivin on other colon cancer cell lines (DLD-1 and SW-620). Our results suggested that NSAIDs could inhibit proliferation and induce apoptosis in colon cancer cells by inhibition of survivin expression and the Wnt/beta-catenin signaling pathway.