[Show abstract][Hide abstract] ABSTRACT: Ursodeoxycholic acid (UDCA) can prevent chemical and colitis-associated colon carcinogenesis by unknown mechanism(s). One of the processes underlying the chemopreventive action could be the inhibition of proliferation by UDCA. To clarify the antiproliferative mechanism of UDCA, we used p53 wt colon carcinoma cell lines HCT8 and HCT116. UDCA-induced inhibition of proliferation was reversible and was associated with a decrease of the S-phase and an increase of G1 phase population, but not with apoptosis or senescence. The treatment suppressed the expression of c-Myc protein and, as a consequence, of several cell cycle regulatory molecules, including CDK4 and CDK6. Using the HCT8 cell line as a model, we show that UDCA suppresses c-Myc at the protein level. The suppression of c-Myc alone or a simultaneous suppression of CDK4 and of CDK6 kinase is sufficient to inhibit cell proliferation. In sum, we identified c-Myc as a primary UDCA target in colon carcinoma cells. The degradation of c-Myc protein decreases the expression of the cell cycle regulators CDK4 and CDK6, which reversibly slows down the cell cycle. The suppression of these proproliferatory molecules is the likely initial mechanism of antiproliferatory action of UDCA on colon cancer cells.
European journal of cancer prevention: the official journal of the European Cancer Prevention Organisation (ECP) 03/2012; 21(5):413-22. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The role of the mismatch repair (MMR) system in correcting base-base mismatches is well established; its involvement in the response to DNA double strand breaks, however, is less clear. We investigated the influence of the essential component of MMR, the hMLH1 protein, on the cellular response to DNA-double strand breaks induced by treatment with SN-38, the active metabolite of topoisomerase I inhibitor irinotecan, in a strictly isogenic cell system (p53(wt), hMLH1(+)/p53(wt), hMLH1(-)). By using hMLH1 expressing clones or cells transduced with the hMLH1-expressing adenovirus as well as siRNA technology, we show that in response to SN-38-induced DNA damage the MMR proficient (MMR(+)) cells make: (i) a stronger G2/M arrest, (ii) a subsequent longer tetraploid G1 arrest, (iii) a stronger activation of Chk1 and Chk2 kinases than the MMR deficient (MMR(-)) counterparts. Both Cdk2 and Cdk4 kinases contribute to the basal tetraploid G1 arrest in MMR(+) and MMR(-) cells. Although the Chk1 kinase is involved in the G2/M arrest, neither Chk1 nor Chk2 are involved in the enhancement of the tetraploid G1 arrest. The long-lasting tetraploid G1 arrest of MMR(+) cells is associated with their lower clonogenic survival after SN-38 treatment, the abrogation of the tetraploid G1 arrest resulted in their better clonogenic survival. These data show that the stabilization of the tetraploid G1 arrest in response to double strand breaks is a novel function of the MMR system that contributes to the lesser survival of MMR(+) cells.
International Journal of Cancer 10/2009; 126(12):2813-25. · 6.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: DNA damage induced by the topoisomerase I inhibitor irinotecan (CPT-11) triggers in p53(WT) colorectal carcinoma cells a long term cell cycle arrest and in p53MUT cells a transient arrest followed by apoptosis (Magrini, R., Bhonde, M. R., Hanski, M. L., Notter, M., Scherübl, H., Boland, C. R., Zeitz, M., and Hanski, C. (2002) Int. J. Cancer 101, 23-31; Bhonde, M. R., Hanski, M. L., Notter, M., Gillissen, B. F., Daniel, P. T., Zeitz, M., and Hanski, C. (2006) Oncogene 25, 165-175). The mechanism of the p53-independent apoptosis still remains largely unclear. Here we used five p53WT and five p53MUT established colon carcinoma cell lines to identify gene expression alterations associated with apoptosis in p53MUT cells after treatment with SN-38, the irinotecan metabolite. After treatment, 16 mitosis-related genes were found to be expressed at least 2-fold stronger in the apoptosis-executing p53MUT cells than in the cell cycle-arrested p53WT cells by oligonucleotide microarray analysis. One of the genes whose strong post-treatment expression was associated with apoptosis was the mitotic checkpoint kinase hMps1 (human ortholog of the yeast monopolar spindle 1 kinase). hMps1 mRNA and protein expression were suppressed by the treatment-induced and by the exogenous adenovirus-coded p53 protein. The direct suppression of hMps1 on RNA level or inhibition of its activity by a dominant-negative hMps1 partly suppressed apoptosis. Together, these data indicate that the high expression of mitotic genes in p53MUT cells after SN-38 treatment contributes to DNA damage-induced apoptosis, whereas their suppression in p53WT cells acts as a safeguard mechanism preventing mitosis initiation and the subsequent apoptosis. hMps1 kinase is one of the mitotic checkpoint proteins whose expression after DNA damage in p53MUT cells activates the checkpoint and contributes to apoptosis.
Journal of Biological Chemistry 04/2006; 281(13):8675-85. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The broad-range cyclin-dependent kinase inhibitor 7-hydroxystaurosporine (UCN-01) is known to induce both a G1 cell cycle arrest and apoptosis. The mechanism of UCN-01-induced apoptosis is largely unknown. We analysed the mechanism of cytotoxicity of UCN-01 in four established colon carcinoma cell lines. The cell lines SW48 and LS513 responded to UCN-01 treatment by undergoing apoptosis in a concentration-dependent manner while the cell lines HT-29 and WiDr were completely resistant. Apoptosis in LS513 and SW48 cell lines was concomitant with the suppression of Bcl-x(L) on mRNA and protein level. In contrast, in the apoptosis-resistant cell lines, Bcl-x(L) expression was not affected by UCN-01. Stable overexpression of the Bcl-x(L) protein abrogated UCN-01-triggered apoptosis, but only partially restored growth, indicating that both cell cycle arrest and apoptosis exert the anticancer effect in a coordinated manner. The inhibition of Akt phosphorylation did not correlate with the apoptotic phenotype. UCN-01 inhibited the activating STAT3 phosphorylations on Ser727 and, notably, on Tyr705, but STAT3 did not contribute to Bcl-x(L) expression in colon carcinoma cells. Moreover, we show for the first time that UCN-01 induces apoptosis by suppression of Bcl-x(L) expression. The inhibition of this pathway is a new aspect of cytotoxic and modulatory potential of UCN-01.
[Show abstract][Hide abstract] ABSTRACT: Irinotecan (CPT-11), a recently introduced component of a standard chemotherapy for colorectal cancer, induces in colon cancer cell lines in vitro cell cycle arrest and apoptosis. Since sporadic colon carcinomas exhibit in 50-60% mutations in the p53 gene and in 10-15% an MSI phenotype due in the great majority of the cases to hMLH1 inactivation, we investigated how these lesions influence the cellular effects of CPT-11 by using colorectal carcinoma cell line HCT116 (which has the genotype p53(+/+),hMLH1(-)) and 2 derivative cell lines with the genotypes p53(+/+),hMLH1(+) and p53(-/-),hMLH1(-). CPT-11 treatment induced G2/M arrest in all 3 cell lines within 48 hr. In the p53(+/+),hMLH1(+) cell line, G2/M arrest was maintained for at least 12 days. There was little concomitant apoptosis, but this was enhanced when the hMLH1 protein was absent. This enhanced apoptosis was accompanied by a shorter duration of the G2/M arrest than in the hMLH1(+) cell line. Partial abrogation of G2/M arrest by caffeine enhanced apoptosis in both hMLH1(+) and hMLH1(-) cells. By contrast, in the p53(-/-) cell line, the G2/M arrest was terminated within 4 days. Termination of the G2/M arrest was accompanied by a high level of apoptosis detectable through poly(ADP-ribose)polymerase (PARP) cleavage, DNA fragmentation and by the appearance of cells with a DNA content <2N. The triggering of G2/M arrest was accompanied in the 3 cell lines by a transient phosphorylation of cdc-2, while the maintenance of the arrest in the p53(+/+) cell lines was accompanied by the overexpression of p53 and p21 proteins and, consequently, by the inhibition of cdc-2 kinase activity. These data indicate that: (i) CPT-11 induces long-term arrest in p53(+/+) cells and a short-term arrest followed by apoptosis in p53(-/-) cells; (ii) triggering of the arrest is p53 independent and is associated with a brief increase of phosphorylation of cdc-2, while the p53-dependent maintenance of G2/M arrest is associated with the inhibition of cdc-2 kinase activity by p21; and (iii) lack of hMLH1 protein enhances CPT-11-induced apoptosis. These results may be useful for designing rational therapies dependent on the p53 and mismatch-repair status in the tumor.
International Journal of Cancer 10/2002; 101(1):23-31. · 5.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Photoluminescence from Si implanted silica is studied as a function of Si fluence and Si concentration profile in order to assess the effect of particle size and size distribution on emission spectra. Peaked (skewed Gaussian) concentration profiles were produced by implanting with 400 keV Si ions and uniform Si profiles were produced by a multi-energy implant sequences. Both as-implanted and annealed samples are shown to exhibit a distinct maximum in the emission intensity as a function of ion fluence, with the intensity increasing with fluence up to the maximum and then decreasing at higher fluences. Samples with a uniform Si profile are also shown to produce emission which is significantly red-shifted relative to that of samples with a peaked Si profile. This is consistent with the fact that such samples are expected to have a narrower particle size distribution (i.e. a greater fraction of larger particles).
Journal of Luminescence 01/1998; 80(1). · 2.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Immunohistochemical data indicate that the frequency of p53 protein overexpression is consistently lower in the mucinous than in the non-mucinous carcinomas of the breast, ovary, pancreas and colon. This peculiar immunohistochemical behavior of the mucinous phenotype could be due to the effect of large amounts of mucus on the staining or to an actual mutation frequency difference between mucinous and non-mucinous carcinomas. This question was investigated on a group of mucinous colorectal carcinomas. DNA was extracted from paraffin sections of 16 human mucinous colorectal carcinomas and the mutation frequency was determined by sequencing of p53 exons amplified in PCR. The expression of p53 protein was determined with the avidin-biotin complex-peroxidase staining procedure and CM-1 antiserum. Twenty-five percent of the tumors exhibited p53 protein overexpression and in 31% a mutation was detected. Concordance between the two techniques was found in 69% of tumors. Overexpression without mutation was observed in 12% and mutation without overexpression in 19%. G:C → A:T transitions represented the most frequent lesion (80%), as previously observed in non-mucinous colorectal carcinomas. These data indicate that the mutation pattern in the p53 gene is similar in mucinous and non-mucinous colorectal carcinomas. The low frequency of p53 overexpression in the mucinous phenotype is not due to a mucus effect on the staining but is related to the low mutation frequency of p53 gene. These results lead to the hypothesis that in contrast to the non-mucinous tumors the development of the majority of colonic carcinomas with the mucinous phenotype may be independent from p53 mutations.