Regulation of transcription of the glutathione S-transferase P1 gene by methylation of the minimal promoter in human leukemia cells

BCR-ABL1-induced downregulation of WASP in chronic myeloid leukemia involves epigenetic modification and contributes to malignancy

Chronic myeloid leukemia (CML) is a myeloproliferative disease caused by the BCR–ABL1 tyrosine kinase (TK). The development of TK inhibitors (TKIs) revolutionized the treatment of CML patients. However, TKIs are not effective to those at advanced phases when amplified BCR–ABL1 levels and increased genomic instability lead to secondary oncogenic modifications. Wiskott–Aldrich syndrome protein (WASP) is an important regulator of signaling transduction in hematopoietic cells and was shown to be an endogenous inhibitor of the c-ABL TK. Here, we show that the expression of WASP decreases with the progression of CML, inversely correlates with the expression of BCR–ABL1 and is particularly low in blast crisis. Enforced expression of BCR–ABL1 negatively regulates the expression of WASP. Decreased expression of WASP is partially due to DNA methylation of the proximal WASP promoter. Importantly, lower levels of WASP in CML advanced phase patients correlate with poorer overall survival (OS) and is associated with TKI response. Interestingly, enforced expression of WASP in BCR–ABL1-positive K562 cells increases the susceptibility to apoptosis induced by TRAIL or chemotherapeutic drugs and negatively modulates BCR–ABL1-induced tumorigenesis in vitro and in vivo. Taken together, our data reveal a novel molecular mechanism that operates in BCR–ABL1-induced tumorigenesis that can be used to develop new strategies to help TKI-resistant, CML patients in blast crisis (BC).

Dual glutathione-S-transferase-θ1 and -μ1 gene deletions determine imatinib failure in chronic myeloid leukemia

Approximately 40% of patients with chronic myeloid leukemia (CML) receiving imatinib fail treatment. There is an increased risk of CML in subjects with (i) deletions of genes encoding glutathione-S-transferase (GST)-θ1 (GSTT1) and -μ1, (GSTM1) and (ii) the GST-π1 (GSTP1) single-nucleotide polymorphism (SNP) Ile105Val (GSTP1*B; rs1695); however, their effects on imatinib treatment outcome are not known. Here, we assess the role of these GSTs in relation to imatinib treatment outcome in 193 CML patients. Deletion of GSTT1 alone, or in combination with deletion of the GSTM1 gene, significantly increased the likelihood of imatinib failure (P = 0.021 and P < 0.001, respectively). The GSTP1*B SNP was not associated with time to imatinib failure. Losses of the GSTT1 and GSTM1 genes are therefore important determinants of imatinib failure in CML. Screening for GSTT1 and GSTM1 gene deletions during diagnosis may identify patients who may be better treated using an alternative therapy.

Regulation of epigenetic traits of the glutathione S-transferase P1 gene: from detoxification toward cancer prevention and diagnosis

Glutathione S-transferases (GSTs) are phase II drug detoxifying enzymes that play an essential role in the maintenance of cell integrity and protection against DNA damage by catalyzing the conjugation of glutathione to a wide variety of exo- and endogenous electrophilic substrates. Glutathione S-transferase P1 (GSTP1), the gene encoding the pi-class GST, is frequently inactivated by acquired somatic CpG island promoter hypermethylation in multiple cancer subtypes including prostate, breast, liver, and blood cancers. Epigenetically mediated GSTP1 silencing is associated with enhanced cancer susceptibility by decreasing its “caretaker” gene function, which tends to promote neoplastic transformation allowing cells to acquire additional alterations. Thus, this epigenetic alteration is now considered as a cancer biomarker but could as well play a driving role in multistep cancer development, especially well documented in prostate cancer development. The present review discusses applications of epigenetic alterations affecting GSTP1 in cancer medicine used alone or in combination with other biomarkers for cancer detection and diagnosis as well as for future targeted preventive and therapeutic interventions including by dietary agents.

Ethacrynic acid and a derivative enhance apoptosis in arsenic trioxide-treated myeloid leukemia and lymphoma cells: the role of glutathione S-transferase p1-1

PURPOSE

Arsenic trioxide (ATO) as a single agent is used for treatment of acute promyelocytic leukemia (APL) with minimal toxicity, but therapeutic effect of ATO in other types of malignancies has not been achieved. We tested whether a combination with ethacrynic acid (EA), a glutathione S-transferase P1-1 (GSTP1-1) inhibitor, and a reactive oxygen species (ROS) inducer will extend the therapeutic effect of ATO beyond APL.

EXPERIMENTAL DESIGN

The combined apoptotic effects of ATO plus ethacrynic acid were tested in non-APL leukemia and lymphoma cell lines. The role of ROS, GSTP1-1, glutathione (GSH), and Mcl-1 in apoptosis was determined. The selective response to this combination of cells with and without GSTP1-1 expression was compared.

RESULTS

ATO/EA combination synergistically induced apoptosis in myeloid leukemia and lymphoma cells. This treatment produced high ROS levels, activated c-jun-NH(2)-kinase (JNK), and reduced Mcl-1 protein. This led to the decrease of mitochondrial transmembrane potential, release of cytochrome c, and subsequently, to activation of caspase-3 and -9. Induction of apoptosis in leukemia and lymphoma cells expressing GSTP1-1 required high ethacrynic acid concentrations to be combined with ATO. Silencing of GSTP1 in leukemia cells sensitized them to ATO/EA-induced apoptosis. In a subgroup of B-cell lymphoma, which does not express GSTP1-1, lower concentrations of ethacrynic acid and its more potent derivative, ethacrynic acid butyl-ester (EABE), decreased intracellular GSH levels and synergistically induced apoptosis when combined with ATO.

CONCLUSION

B-cell lymphoma cells lacking GSTP1-1 are more sensitive than myeloid leukemia cells to ATO/EA-induced apoptosis.

Constitutive expression of an antioxidant enzyme, glutathione S-transferase P1, during differentiation of human intestinal Caco-2 cells

In this study, we investigated the molecular mechanism of the constitutive expression of an antioxidant enzyme, glutathione S-transferase (GST), during differentiation of human intestinal epithelial Caco-2 cells. We observed that the class π GST isozyme (GST P1) expression correlated with the increased expression of caudal-related homeodomain protein 2 (CDX2), a member of the mammalian homeobox family of transcription factors. In addition, transfection of Caco-2 cells with the human CDX2 cDNA resulted in enhanced expression of the GST P1 gene and protein. Chromatin immunoprecipitation assay demonstrated that CDX2 binds to the GST P1 promoter containing the putative consensus CDX-binding element, TTTAC, located at -247 upstream from the established site for transcription initiation. Using the dsDNA pull-down assay, it was revealed that CDX2 recognized and bound to the putative consensus CDX-binding element within the human GST P1 promoter region and that the amount of the CDX2 bound to the putative consensus CDX-binding element increased during Caco-2 cell differentiation. Furthermore, we demonstrated that CDX2 formed the transcriptional complex with Sp1 and bound to the putative consensus CDX-binding element within the human GST P1 promoter region. These data suggest that CDX2 binds to the human GST P1 promoter via complex formation with Sp1 and controls the constitutive expression of GST P1 during Caco-2 cell differentiation.

Reversible epigenetic fingerprint-mediated glutathione-S-transferase P1 gene silencing in human leukemia cell lines

Glutathione-S-transferase P1 (GSTP1) gene is commonly silenced by CpG island promoter hypermethylation in prostate, breast, and liver cancers. However, mechanisms leading to GSTP1 repression by promoter hypermethylation in leukemia and its relationship with pathological alterations of the chromatin structure remain poorly understood. A panel of leukemia cell lines was analyzed for their GSTP1 expression, revealing cell lines with high, moderate or no detectable GSTP1 expression. Bisulfite sequencing, methylation-specific PCR and combined bisulfite restriction analysis revealed that GSTP1 promoter was completely methylated in transcriptionally inactive RAJI and MEG-01 cell lines. In contrast, cell lines expressing GSTP1 exhibited an unmethylated and transcriptionally active promoter. Furthermore, histone marks and effector proteins associated with transcriptional activity were detected by chromatin immunoprecipitation in the GSTP1 expressing hypomethylated K-562 cell line. However, repressive chromatin marks and the recruitment of silencing protein complexes were found in the non-expressing hypermethylated RAJI and MEG-01 cell lines. Finally, we provide evidence that treatment of RAJI and MEG-01 cells with the DNA demethylating agent, 5-aza-2'-deoxycytidine, resulted in GSTP1 promoter demethylation, drastic changes of histone modifications and promoter associated proteins and GSTP1 gene activation. In contrast, treatments with HDAC inhibitors failed to demethylate and reactivate the GSTP1 gene. Our study extends the knowledge on leukemia-specific epigenetic alterations of GSTP1 gene. Furthermore, we are showing the correlation of DNA methylation and histone modifications with the positive/negative GSTP1 transcriptional expression state. Finally, these data support the concept of the dominance of DNA methylation over HDAC inhibitor-sensitive histone deacetylation in gene silencing.

Transcriptional and post-transcriptional regulation of glutathione S-transferase P1 expression during butyric acid-induced differentiation of K562 cells

Over-expression of glutathione S-transferase P1 is related to chemotherapeutic drug resistance as well as to differentiation of human erythroleukemia cells. In opposition to previously described differentiating inducers which enhance the GST-resistance phenotype, time- and concentration-dependent activation of both erythroid and megakaryocytic differentiation pathways by butyric acid progressively diminished GSTP1 mRNA expression. GSTP1 mRNA expression decreased by 25% (p<0.01) and 64% (p<0.01) in 1mM and 2mM butyric acid-differentiated K562 cells, respectively. These results were associated to both a reduction of GATA-1 binding activity to the GSTP1 promoter and to a posttranscriptional destabilization of GSTP1 mRNA in a concentration dependent manner. Indeed, GSTP1 mRNA half-life decreased from 43.8 to 36.2 h and 12.6 h in 1mM- and 2mM-treated cells, respectively.

Upstream CpG island methylation of the PAX3 gene in human rhabdomyosarcomas

BACKGROUND

Adult tumors can be characterized by hypermethylation of CpG islands associated with 5'-upstream and coding regions of specific genes. This hypermethylation can also be part of the aging process. In contrast, much less is known about gene hypermethylation in childhood cancers, where methylation changes are not part of the aging process but likely represent developmental dysregulation. PAX3 is an important gene in muscle development and muscle-producing neoplasms such as rhabdomyosarcomas.

PROCEDURES

We examined the methylation status of a PAX3 5'-CpG island in rhabdomyosarcoma subtypes and in normal fetal skeletal muscle. PAX3 methylation was analyzed in 15 embryonal rhabdomyosarcomas, 12 alveolar rhabdomyosarcomas, and in six normal skeletal muscle samples, using semi-quantitative PCR analysis of DNA digested with methyl-sensitive restriction enzymes.

RESULTS

The CpG island in the upstream region of the human PAX3 gene was hypermethylated in the majority of ERMS examined (13 of 15 tumors, mean of 52% methylation), whereas most ARMS (9 of 12 tumors) and all normal muscle samples showed relative hypomethylation (both 18% mean methylation). Various CpG sites differ in contribution to overall PAX3 CpG island methylation, with methylation at a HaeII site being inversely correlated with PAX3 expression.

CONCLUSIONS

PAX3 CpG island methylation appears to distinguish embryonal subtype of rhabdomyosarcoma from alveolar, and methylation at certain sites within this CpG island is inversely correlated with PAX3 expression. In addition to exemplifying developmental dysregulation, methylation of PAX3 has potential in the development of an epigenetic profile for the diagnosis of rhabdomyosarcoma.

Gene therapy of adenovirus mediated CD∷upp/5-FC directed by GSTP1 promoter in cisplatin-resistant ovarian cancer

PURPOSE

To evaluate the specific killing effect of the adenoviral vector in which CD ::upp genes were directed by the GSTP1 promoter on cisplatin-resistant ovarian cancer cells.

EXPERIMENTAL DESIGN

Cisplatin-sensitive (A2780) and cisplatin-resistant (AD6) ovarian cancer cells were infected with recombinant adenoviral plasmid carrying the CD ::upp gene driven by the GSTP1 promoter and followed with 5-FC administration.

RESULTS

In vitro, when MOI was 100 and 5-FC was 250 microg/ml, relative survival rate of the AD6 cells was only 3.63 +/- 1.01%, while under the same conditions, A2780 cells were 76.50 +/- 2.81%. Significant bystander effect was caused by the CD ::upp gene and 20% of gene-transferred AD6 cells caused death to 80.3% of the total cells. Furthermore, a significant anti-tumor effect of the Ad.GST-CD ::upp/5-FC was observed in nude mice bearing tumors of AD6 cells.

CONCLUSIONS

These results indicated that adenovirus-mediated Ad.GST-CD ::upp/5-FC directed by GSTP1 promoter is an effective approach to overcome cisplatin-resistant ovarian cancer.

Epigenetic changes in prostate cancer: implication for diagnosis and treatment

Prostate cancer is the most common noncutaneous malignancy and the second leading cause of cancer death among men in the United States. DNA methylation and histone modifications are important epigenetic mechanisms of gene regulation and play essential roles both independently and cooperatively in tumor initiation and progression. Aberrant epigenetic events such as DNA hypo- and hypermethylation and altered histone acetylation have both been observed in prostate cancer, in which they affect a large number of genes. Although the list of aberrantly epigenetically regulated genes continues to grow, only a few genes have, so far, given promising results as potential tumor biomarkers for early diagnosis and risk assessment of prostate cancer. Thus, large-scale screening of aberrant epigenetic events such as DNA hypermethylation is needed to identify prostate cancer-specific epigenetic fingerprints. The reversibility of epigenetic aberrations has made them attractive targets for cancer treatment with modulators that demethylate DNA and inhibit histone deacetylases, leading to reactivation of silenced genes. More studies into the mechanism and consequence of demethylation are required before the cancer epigenome can be safely manipulated with therapeutics as a treatment modality. In this review, we examine the current literature on epigenetic changes in prostate cancer and discuss the clinical potential of cancer epigenetics for the diagnosis and treatment of this disease.

Glutathione-S-transferase π inhibits As2O3-induced apoptosis in lymphoma cells: involvement of hydrogen peroxide catabolism

Arsenic trioxide (As2O3) is an effective agent for the treatment of relapsed and refractory acute promyelocytic leukemia by induction of partial differentiation and apoptosis. As2O3, at therapeutic concentrations (1-2 μM), induced apoptosis in Raji lymphoma cells but not in Jurkat lymphoma cells, which inversely correlated with the levels of glutathione-S-transferase π (GSTP1), but not GSTπ1 and GSTM1, expression and activity. GSTP1 mRNA, protein level, and activity were high in Jurkat cells but undetectable in Raji cells. Stable transfection of GSTP1 into Raji cells decreased the amount of As2O3-induced apoptosis. Apoptosis induced by therapeutic concentrations of As2O3 in Raji cells is related to increasing H2O2 intracellular accumulation but not to JNK activation. Forced expression of GSTP1 by transfection of Raji cells significantly decreased the basal amount of H2O2 and its levels after therapeutic concentration of As2O3 treatment. Added exogenous H2O2 was removed more rapidly, which correlated with a greater decrease in reduced glutathione level in Raji clones expressing GSTP1 than in those clones without GSTP1 expression. Overexpression of GSTP1 in transfected Raji clones was also found to decrease the retention of As2O3. These data suggest that GSTP1 blocks As2O3-induced apoptosis in lymphoma cells by decreasing intracellular amounts of H2O2 by catabolism and H2O2 production by decreasing the intracellular retention of As2O3.

Expression of glutathione S-transferase P1-1 in leukemic cells is regulated by inducible AP-1 binding

Glutathione S-transferases (GST) are involved in cellular protection against xenobiotics, oxidative stress as well as in resistance against chemotherapeutic compounds such as doxorubicin. Levels of human placental type GSTP1-1 are known to be increased in many tumors and hematopoietic diseases. In this work, we compare transcriptional mechanisms in cells that express or not GSTP1-1. Transient transfection assays are used to show that different GST-promoter reporter constructs generate cell-type specific levels of luciferase activity. In expressing cells, transcriptional activity is strongly dependent on AP-1 binding elements within the -65 to -75 bp region of the GSTP1 gene as shown by site-directed mutagenesis. Electrophoretic mobility shift assays show that DNA binding activity is exclusively observed in GSTP1-1-expressing cells and is increased after stimulation with hydrogen peroxide, TPA, tert-butylhydroquinone and doxorubicin. Non-expressing cells present neither constitutive nor inducible AP-1 binding. Taken together, our results provide evidence for the induction of the GSTP1 gene via AP-1 binding activity in leukemia cells and contribute to a better understanding of the molecular events regulating genes involved in drug resistance mechanisms.

A methylated oligonucleotide induced methylation of GSTP1 promoter and suppressed its expression in A549 lung adenocarcinoma cells

Glutathione S-transferase P1 (GSTP1) belongs to xenobiotic enzymes, and is supposed to contribute to chemoresistance. Though it was reported that GSTP1 gene is suppressed by cytosine-guanine (CpG) island methylation of its promoter, this promoter is not strongly methylated and GSTP1 protein is highly expressed in lung cancer. We intended to induce methylation of GSTP1 CpG island by using a methylated sense oligonucleotide complementary to this region. When we transduced the methylated oligonucleotides to A549 lung adenocarcinoma cells, methylation of the GSTP1 promoter and reduction of GSTP1 expression was induced, cell viability was reduced; however, chemoresistance against cisplatin has not clearly changed.

Regulation of glutathione S-transferase P1-1 gene expression by NF-kappaB in tumor necrosis factor alpha-treated K562 leukemia cells

Glutathione S-transferases (GSTs) play an important role in the protection of cells against xenobiotics and lipid hydroperoxides generated by oxidative stress. In human, the GSTP1-1 expression is commonly increased in many tumors and involved in the development of antineoplastic drug resistance. Reactive oxygen species are released at inflammation sites and oxidative stress conditions enhance the expression of genes encoding antioxidant enzymes such as GSTs. Here we investigated the regulation of the GSTP1-1 gene expression in the K562 cell line by nuclear factor kappaB (NF-kappaB) and the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha). By studying GSTP1-1 mRNA expression and NF-kappaB/GSTP1-1 promoter interactions, we showed the implication of NF-kappaB in the GSTP1-1 gene expression and we described a new specific TNFalpha-inducible NF-kappaB binding site upstream of the minimal promoter. Moreover, TNFalpha treatment as well as cotransfection of NF-kappaB signaling pathway intermediates induced an activation of the GSTP1-1 gene promoter in K562 cells. Site-directed mutagenesis of the NF-kappaB site strongly inhibited TNFalpha- and NF-kappaBp65-induced promoter activation. Altogether, we showed that a sequence located at -323/-314 within the GSTP1-1 promoter bound NF-kappaB p50/65 and p65/p65 dimers and that this kappaB site was involved in the regulation of the gene by TNFalpha.

Control mechanisms in the regulation of telomerase reverse transcriptase expression in differentiating human teratocarcinoma cells

Telomerase is active in about 90% of cancers and contributes to the immortality of cancer cells by maintaining the lengths of the ends of chromosomes. Undifferentiated embryonic human teratocarcinoma (HT) cells were found to express high levels of hTERT, the catalytic subunit of telomerase, and the hTERT promoter was unmethylated in these cells. Retinoic acid (RA)-induced differentiation led to hTERT gene silencing and increased methylation of the hTERT promoter. Treatment with trichostatin A, a histone deacetylase inhibitor, resulted in hTERT reactivation only in very early differentiating HT cells. After methylation patterns had been established within the hTERT promoter region in late differentiating cells, 5-azacytidine, a common demethylating agent, activated the hTERT gene but trichostatin A had no effect on hTERT transcription. These studies suggest that histone deacetylation is involved in early hTERT gene down-regulation and that DNA methylation may maintain silencing of the hTERT gene in these cells.

CpG island methylation of tumor-related genes in three primary central nervous system lymphomas in immunocompetent patients

We have determined the promoter CpG island methylation status of O(6)-methylguanine-DNA methyltransferase (MGMT), glutathione-S-transferase P1 (GSTP1), death-associated protein kinase (DAPK), p14(ARF), thrombospondin-1 (THBS1), tissue inhibitor of metalloproteinase-3 gene (TIMP-3), p73, p16(INK4A), RB1, and TP53 genes in three primary central nervous system lymphomas (PCNSL). Five genes (GSTP1, DAPK, TIMP-3, p16(INK4A), and RB1) were hypermethylated in two samples, whereas MGMT, THBS1, and p73 were aberrantly methylated in only one sample. No case presented CpG island methylation for the p14(ARF) and TP53 genes. These findings concur with previous data suggesting a frequent inactivation of p16(INK4A) and very limited involvement of TP53 in PCNSL and also provide insights into the epigenetic molecular involvement of other tumor-related genes in this neoplasm.

A methylated oligonucleotide inhibits IGF2 expression and enhances survival in a model of hepatocellular carcinoma

IGF-II is a mitogenic peptide that has been implicated in hepatocellular oncogenesis. Since the silencing of gene expression is frequently associated with cytosine methylation at cytosine-guanine (CpG) dinucleotides, we designed a methylated oligonucleotide (MON1) complementary to a region encompassing IGF2 promoter P4 in an attempt to induce DNA methylation at that locus and diminish IGF2 mRNA levels. MON1 specifically inhibited IGF2 mRNA accumulation in vitro, whereas an oligonucleotide (ON1) with the same sequence but with nonmethylated cytosines had no effect on IGF2 mRNA abundance. MON1 treatment led to the specific induction of de novo DNA methylation in the region of IGF2 promoter hP4. Cells from a human hepatocellular carcinoma (HCC) cell line, Hep 3B, were implanted into the livers of nude mice, resulting in the growth of large tumors. Animals treated with MON1 had markedly prolonged survival as compared with those animals treated with saline or a truncated methylated oligonucleotide that did not alter IGF2 mRNA levels in vitro. This study demonstrates that a methylated sense oligonucleotide can be used to induce epigenetic changes in the IGF2 gene and that inhibition of IGF2 mRNA accumulation may lead to enhanced survival in a model of HCC.

A methylated oligonucleotide inhibits IGF2 expression and enhances survival in a model of hepatocellular carcinoma

IGF-II is a mitogenic peptide that has been implicated in hepatocellular oncogenesis. Since the silencing of gene expression is frequently associated with cytosine methylation at cytosine-guanine (CpG) dinucleotides, we designed a methylated oligonucleotide (MON1) complementary to a region encompassing IGF2 promoter P4 in an attempt to induce DNA methylation at that locus and diminish IGF2 mRNA levels. MON1 specifically inhibited IGF2 mRNA accumulation in vitro, whereas an oligonucleotide (ON1) with the same sequence but with nonmethylated cytosines had no effect on IGF2 mRNA abundance. MON1 treatment led to the specific induction of de novo DNA methylation in the region of IGF2 promoter hP4. Cells from a human hepatocellular carcinoma (HCC) cell line, Hep 3B, were implanted into the livers of nude mice, resulting in the growth of large tumors. Animals treated with MON1 had markedly prolonged survival as compared with those animals treated with saline or a truncated methylated oligonucleotide that did not alter IGF2 mRNA levels in vitro. This study demonstrates that a methylated sense oligonucleotide can be used to induce epigenetic changes in the IGF2 gene and that inhibition of IGF2 mRNA accumulation may lead to enhanced survival in a model of HCC.

Insulin-like growth factor-1 inscribes a gene expression profile for angiogenic factors and cancer progression in breast epithelial cells

Activation of the insulin-like growth factor-1 receptor (IGF-1R) by IGF-1 is associated with the risk and progression of many types of cancer, although despite this it remains unclear how activated IGF-1R contributes to cancer progression. In this study, gene expression changes elicited by IGF-1 were profiled in breast epithelial cells. We noted that many genes are functionally linked to cancer progression and angiogenesis. To validate some of the changes observed, the RNA and/or protein was confirmed for c-fos, cytochrome P450 1A1, cytochrome P450 1B1, interleukin-1 beta, fas ligand, vascular endothelial growth factor, and urokinase plasminogen activator. Nuclear proteins were also temporally monitored to address how gene expression changes were regulated. We found that IGF-1 stimulated the nuclear translocation of phosphorylated AKT, hypoxic-inducible factor-1 alpha, and phosphorylated cAMP-responsive element-binding protein, which correlated with temporal changes in gene expression. Next, the promoter regions of IGF-1-regulated genes were searched in silico. The promoters of genes that clustered together had similar regulatory regions. In summary, IGF-1 inscribes a gene expression profile relevant to cancer progression, and this study provides insight into the mechanism(s) whereby some of these changes occur.

Loss of glutathione S-transferase (GST) mu phenotype in colorectal adenocarcinomas from patients with a GSTM1 positive genotype

Glutathione S-transferase (GST) mu phenotype was assessed in colon tissue from patients with ulcerative colitis and colorectal neoplasms that were positive for GSTM1 genotype. GST mu protein (enzyme linked immunosorbent assay) was absent in 2/9 unaffected colon tissue (22.3%), 4/13 tissues with chronic ulcerative colitis (CUC) (30.7%), 4/11 adenomas (36.4%) and 7/14 adenocarcinomas (50.0%; P<or=0.05). GST-3H-trans-stilbene oxide activity was detected in all tissues except 1/13 (7.6%) CUC tissues and 7/14 (50.0%, P<or=0.05) colorectal adenocarcinomas. Immunoreactive GST mu was observed in colonic epithelial cells but not in adjacent neoplastic cells by immunohistochemistry. Two-dimensional electrophoresis revealed several mu class isoforms in cytosol from unaffected colon that were absent in matched tumor cytosol. These results indicate that GSTM1 genotype may not necessarily reflect GST mu phenotype in colorectal tumors.