Strong expression of methylthioadenosine phosphorylase (MTAP) in human colon carcinoma cells is regulated by TCF1/[beta]-catenin

Abstract

Methylthioadenosine phosphorylase (MTAP) is known as a ubiquitously expressed house keeping gene important in biochemical salvage processes. The MTAP gene is localized on the human chromosomal region 9p21, a region often deleted in cancer. Recently, several groups including our own have shown that MTAP serves as a tumour suppressor gene. The aim of this study was to analyse the role of MTAP in colon carcinoma and normal colon epithelium and the regulation of gene expression. To examine MTAP RNA and protein expression, we screened six colon carcinoma cell lines and human primary colon epithelial cells by RT-PCR and immunoblotting. MTAP expression was confirmed in vivo by immunohistochemical staining of normal colon tissue compared to adenoma and colon carcinoma. Interestingly, we found strong MTAP mRNA and protein expression by colon carcinoma cell lines but no expression by colonic epithelial cells. To analyse the regulation of MTAP expression, promoter studies were performed and revealed control of MTAP expression by LEF/TCF/bcatenin. Furthermore, we demonstrated a significant correlation between MTAP protein expression and tumour progression as the intensity of MTAP protein staining increased from normal tissue to carcinoma. In addition, the recently postulated association between MTAP activity and interferon (IFN) sensitivity was confirmed in colon epithelial cells showing only little response to IFN-gamma, in contrast to the carcinoma cell lines. In summary, these data indicate for the first time that MTAP is not expressed in normal human colonic epithelium but is strongly upregulated in colon carcinoma. This finding may be of clinical significance concerning the homeostasis of normal colon epithelium and potential treatment of colon carcinoma. Laboratory Investigation ( 2.28) plays a major role in polyamine metabolism and is important for the salvage of both adenine and methionine. MTAP catalyses the phosphorylation of methylthioadenosine (MTA), a by-product of the synthesis of polyamines, which acts as a potent inhibitor of polyamine aminopropyltransferase and methyltransferases. MTAP has been shown previously to be expressed abundantly in normal cells and tissues. 1 In contrast, many malignant cells lack MTAP activity, 2-5 and cultured MTAP-deficient cells secrete MTA instead of metabolising it. 6 The reason for the frequent loss of MTAP activity became evident after determining the chromosomal location of MTAP. Starting from the centromeric end, the gene order on human chromosome 9p21 was mapped as p15-p16-MTAP-interferon(IFN)-alpha-IFNbeta. 1 In this region, many tumours reveal selective deletions. Recently, MTAP gene deletions were described in endometrial cancer, osteosarcoma and in haematological neoplasias like lymphoblastic leukaemia or non-Hodgkin's lymphomas. [2][3][4][5] In addition to its role in polyamine metabolism, MTAP expression has recently been shown to have significant impact on signal transducer and activator of transcription (STAT) 1 activity. 7 STAT1 is

Tissue Microarray Analysis of Methylthioadenosine Phosphorylase Protein Expression in Melanocytic Skin Tumors

“…6 In contrast, MTAP was not expressed in normal human colon epithelium but was strongly up-regulated in colon carcinoma. 7 In addition, MTAP expression has been shown to have a significant effect on STAT1 (signal transducer and activator of transcription 1) activity.…”

“…performed a blinded evaluation of the stained slides. Based on the method of Bataille et al, 7 cytoplasmic MTAP staining intensity was estimated using a semiquantitative 3-step scoring system (range, 0-2) as follows: 0, negative; 1, weak positive; and 2, strong positive. Because of the small tissue amounts of each individual tumor on the TMAs, weak MTAP immunoreactivity was considered positive.…”

“…6,7 In brief, tissues were deparaffinized, rehydrated, and incubated with primary polyclonal chicken anti-MTAP antibody (1:1 500) overnight at 4°C. The secondary antibody (biotin-labeled antichicken, 1:1 000; Jackson ImmunoResearch Laboratories, Ltd, West Grove, Pa) was incubated for 30 minutes at room temperature, followed by incubation with streptavidin-peroxidase (Dako Cytomation GmbH, Hamburg, Germany) for 30 minutes.…”

Reduced expression of TANGO in colon and hepatocellular carcinomas

“…A significant reduction or even loss of TANGO mRNA expression was found in all hepatocellular tumor cell lines compared to PHH and in all colon tumor cell lines compared to normal CECs. The cell line HT29M3 is a modified HT29 cell line resembling rather normal colon epithelial cells (20) and was added to the expression analysis. This cell line re-expresses high amounts of TANGO compared to the colon tumor cell line HT29.…”

Suppressive effects of tumor cell-derived 5′-deoxy-5′-methylthioadenosine on human T cells

“…It is constitutively expressed in almost all cells and tissues. 18,19 Mtap ¡/¡ mice are embryonic lethal. 20 In malignant melanoma, MTAP deficiency leads to increased invasiveness 13 and poor response to adjuvant therapy with Interferon-a (IFN-a).…”