Effects of nonsteroidal anti-inflammatory drugs on proliferation and on induction of apoptosis in colon cancer cells by a prostaglandin-independent pathway

Sulindac sulfide induces several subpopulations of colon cancer cells, defined by PCNA/Ki-67 and DNA strand breaks

We assessed the effect of sulindac sulfide (SS), a colon cancer chemopreventive agent, on the proliferation and apoptosis in the colon cancer cell lines HCT-15 and HT-29. We applied a triparameter flow cytometric analysis that simultaneously determined DNA content, expression of Ki-67 or proliferating cell nuclear antigen (PCNA), and extent of DNA strand breaks by TUNEL (TdT-mediated dUTP nick end labeling). HCT-15 and HT-29 cells were exposed to SS 200 microM and 175 microM, respectively, for up to 72 h. As expected, SS inhibited proliferation and induced apoptosis. SS also induced several subpopulations of cells defined by their expression of proliferation markers and DNA strand breaks. By 72 h the rapidly proliferating cells [PCNA/Ki-67(+)/TUNEL(-)] were reduced from > 90% to about one third. Of the remaining cells, about one third were apoptotic [PCNA/Ki-67(-)/TUNEL(+)] and one third were quiescent [PCNA/Ki-67(-)/TUNEL(-)]. Another subpopulation was detected that was PCNA/Ki-67(+)/TUNEL(+), some had a dominant subdiploid peak and over half were in S or G2/M phases by DNA content. Thus, a subpopulation of apoptotic cells strongly expressed PCNA and Ki-67, suggesting that their specificity as proliferation markers may need reassessment. Similar results were obtained with the HL-60 promyelocytic cell line.

Curcumin, a natural plant phenolic food additive, inhibits cell proliferation and induces cell cycle changes in colon adenocarcinoma cell lines by a prostaglandin-independent pathway

Curcumin, the active ingredient of the rhizome of the plant turmeric (Curcuma longa Linn), a commonly used spice, prevents cancer in animal tumor models. Its mechanism of action is unknown; curcumin may act by inhibiting arachidonic acid metabolism. To explore the mechanism of curcumin's chemopreventive effect, we studied its role in proliferation and apoptosis in the HT-29 and HCT-15 human colon cancer cell lines. Curcumin dose-dependently reduced the proliferation rate of both cell lines, causing a 96% decrease by 48 hours. No apoptosis was detected. The antiproliferative effect was preceded by accumulation of the cells in the G2/M phase of cell cycle. The effect of curcumin was similar in both cell lines, which, however, differ in their ability to produce prostaglandins. We conclude that curcumin inhibits colon cancer cell proliferation in vitro mainly by accumulating cells in the G2/M phase and that this effect is independent of its ability to inhibit prostaglandin synthesis. The role of curcumin's antiproliferative effect in human colon cancer remains to be established.

Physiology and pathophysiology of apoptosis in epithelial cells of the liver, pancreas, and intestine

Cell death of gastrointestinal epithelial cells occurs by a process referred to as apoptosis. In this review, we succinctly define apoptosis and summarize the role of apoptosis in the physiology and pathophysiology of epithelial cells in the liver, pancreas, and small and large intestine. The physiological mediators regulating apoptosis in gastrointestinal epithelial cells, when known, are discussed. Selected pathophysiological consequences of excessive apoptosis and inhibition of apoptosis are used to illustrate the significance of apoptosis in disease processes. These examples demonstrate that excessive apoptosis may result in epithelial cell atrophy, injury, and dysfunction, whereas inhibition of apoptosis results in hyperplasia and promotes malignant transformation. The specific cellular mechanisms responsible for dysregulation of epithelial cell apoptosis during pathophysiological disturbances are emphasized. Potential future areas of physiological research regarding apoptosis in gastrointestinal epithelia are highlighted when appropriate.

Prostaglandin H synthase expression is variable in human colorectal adenocarcinoma cell lines

The expression of prostaglandin H synthases can be induced by many stimuli and is likely to be important in control of the cell cycle. The analysis of prostaglandin H synthase-1 and -2 expression in colon adenocarcinoma cell lines is a useful model system for studying the function of the prostaglandin H synthases, especially with regard to proliferation and adhesion. Prostaglandin H synthase-1 protein is not found in any of eight human colon adenocarcinoma cell lines. Expression of prostaglandin H synthase-2 is variable for the eight cell lines: three constitutively expressed active protein, four did not express this gene at all, and one had mRNA but no active protein. Thus, five colorectal adenocarcinoma cell lines exhibit "null" expression of prostaglandin synthase-2. The three cell lines with constitutive expression of prostaglandin H synthase-2 produce PGE2. Prostaglandin E2 production could be inhibited by aspirin and NS398 without inhibiting proliferation, while direct addition of prostaglandin E2 inhibits proliferation. Adhesion to collagen IV and fibronectin was stronger in those cell lines that expressed prostaglandin H synthase-2. The constitutive expression of prostaglandin H synthase-2 is associated with increased adhesion to extracellular matrix components and a potential inhibition of proliferation through the production of prostaglandin E2. The absence of PGH synthase-2 expression in some cell lines may result from the original tumor's need to inactivate these associated functions. Our evidence suggests that PGH synthase-2 is a possible candidate for a tumor suppressor gene at 1q23-qter.

NSAID-induced apoptosis in Rous sarcoma virus-transformed chicken embryo fibroblasts is dependent on v-src and c-myc and is inhibited by bcl-2

Mounting epidemiological and experimental evidence implicates non-steroidal antiinflammatory drugs as anti-tumorigenic agents. Our previous work showed that nonsteroidal antiinflammatory drug treatment of src-transformed chicken embryo fibroblasts caused apoptosis--a mechanism by which these drugs might exert their anti-tumorigenic effect. The present studies employ a sensitive technique for detecting single- and double-stranded DNA cleavage (the comet assay) to quantitate apoptosis. By this method pp60v-src, which antagonizes apoptosis in many cell systems, was found to induce apoptosis in 11-23% of serum-starved fibroblasts. However, treatment with diclofenac following pp60v-src activation produced a much stronger response beginning within 6 hours of treatment that resulted in 100% lethality. During cell death, cyclooxygenase-2 but not cyclooxygenase-1 mRNA was found to be uniformly increased by all apoptotic drugs tested. Examination of the expression of apoptosis-associated genes showed that c-rel and p53 (found in normal or v-src-transformed chicken embryo fibroblasts at moderate levels), and bcl-2 (present at an extremely low level) were largely unchanged by treatment with eight different nonsteroidal antiinflammatory drugs. However, overexpression of human bcl-2 inhibited diclofenac-mediated apoptosis by 90%, demonstrating directly that bcl-2 expression can regulate nonsteroidal antiinflammatory drug induction of cell death. The proto-oncogene c-myc is known to cause apoptosis in chicken embryo fibroblasts when artificially overexpressed in cells deprived of trophic factors. We found that nonsteroidal antiinflammatory drug treatment following pp60v-src activation persistently induced myc protein and mRNA by more than 20-fold above that evoked by pp60v-src activation alone. Moreover, transfection of antisense c-myc oligonucleotides reduced drug-induced myc expression by 80% and caused a concomitant 50% reduction in cell death. These findings suggest that nonsteroidal antiinflammatory drug-induced apoptosis proceeds through a src/myc dependent pathway which is negatively regulated by bcl-2.

Sulindac sulfide inhibits the proliferation of colon cancer cells: diminished expression of the proliferation markers PCNA and Ki-67

We evaluated the effect of sulindac sulfide (SS), which reduces cell number and induces apoptosis in cultured colon cancer cells (CCCs), on expression of the proliferation markers PCNA and Ki-67 in HT-29 and HCT-15 CCCs; only the former express cyclooxygenases. DNA content and PCNA/Ki-67 expression were analyzed by bivariate flow cytometry. SS inhibited cell proliferation, determined by the reduced expression of PCNA and Ki-67, roughly by half at 72 h, and induced apoptosis (accounting for about two-thirds and one-third of the reduction in cell number, respectively). A similar effect of SS occurred in HT-29 and HCT-15 CCCs, and also in non-colonic cells, indicating that this rather general effect of SS on cultured cells is not dependent on inhibition of prostaglandin synthesis.

The effect of eicosanoids on the expression of MHC genes in cultured human colon cancer cells and mouse colonocytes in vivo

Eicosanoids have been implicated in the pathogenesis of cancer and are known to regulate the expression of antigens of the major histocompatibility complex (MHC). In human colon cancer, we have recently observed that: (a) the expression of MHC class I and II antigens are markedly reduced; and (b) the levels of PGE2, but not of PGF2 alpha and LTB4, are elevated compared to histologically normal mucosa. Therefore, we investigated the effect of PGE2, PGF2 alpha and LTB4 on the regulation of MHC class I antigens in two human colon adenocarcinoma cell lines and in a murine model of colon cancer. None of these eicosanoids had any significant effect on the expression of MHC class I antigens in the human colonocytes or the transcription rate of class I genes, with the exception of LTB4 which only modestly suppressed the transcription rate. Similarly, 16, 16-dimethyl-PGE2 had no effect on the expression of MHC class I genes in the colonocytes of BALB/c mice treated with the carcinogen dimethylhydrazine. We conclude that PGE2, PGF2 alpha and LTB4 did not affect the expression of MHC class I antigens in cultured human colon adenocarcinoma cells, and 16, 16-dimethyl PGE2 did not affect their expression in mice, even when mice were treated with a colon carcinogen. Thus, these eicosanoids are an unlikely regulator of the observed underexpression of MHC class I antigens in human colon cancer.