Context-Dependent Bidirectional Regulation of the MutS Homolog 2 by Transforming Growth Factor β Contributes to Chemoresistance in Breast Cancer Cells

Abstract

The TGF-b, a tumor suppressive cytokine in normal cells, is abused in cancer to promote the malignancy. In this study, we reported that TGF-b downregulated the mutS homolog 2 (MSH2), a central component of the DNA mismatch repair (MMR) system, in HER2-transformed MCF10A mammary epithelial cells and in breast cancer (BC) cells. This was mediated by a TGF-b-induced micro RNA (miRNA), miR-21, which targeted the 3 0 untranslated region of MSH2 mRNA and downregulated its expression. A negative correlation between the expression of TGF-b1 and MSH2 was also detected in primary breast tumors. In contrast, TGF-b upregulated MSH2 in nontransformed cells through Smad-mediated, p53-dependent promoter activation, which was absent in BC cells with impaired p53 function. Although this upregulating mechanism also existed in MCF10A/HER2 and p53-proficient BC cells, both basal and TGF-b-induced MSH2 promoter activities were significantly lower than those in MCF10A. Moreover, the basal and TGF-b-induced miR-21 levels were markedly higher in transformed cells, suggesting that the preset levels of miR-21 and MSH2 promoter activity, which is affected by the p53 status, determine the outputs of the bidirectional regulation of MSH2 by TGF-b in a certain cellular context. We further found that by downregulating MSH2, TGF-b contributed to resistance to DNA-damaging chemotherapy agents in cancer cells. Our results indicated a regulatory antagonism between promoter activation and miRNA-mediated posttranscriptional inhibition underlying a dual effect of TGF-b on the DNA repair machinery, which may influence the genomic stability in a context-dependent manner and contribute to chemoresistance in cancer. Mol Cancer Res; 8(12); 1633-42. Ó2010 AACR.

miR‑21 is involved in transforming growth factor β1‑induced chemoresistance and invasion by targeting PTEN in breast cancer

“…Previous studies have demonstrated that TGF-β1 decreased the sensitivity of cancer cells to chemotherapeutic drugs (8,9). In addition, miR-21 may modulate the chemosensitivity of breast cancer cells to DOX (21).…”

“…Previous studies have demonstrated that TGF-β1 facilitates breast carcinoma metastasis by promoting epithelial-mesenchymal transition (EMT) in tumor cells (6,7). Additionally, TGF-β1 was previously associated with chemoresistance, and increased TGF-β1 levels led to poor clinical outcomes in a number of types of cancer, including breast cancer (8,9). Multiple pathways are involved in TGF-β1 signaling (10); however, the downstream molecular pathways for TGF-β1-mediated breast cancer metastasis and chemoresistance remain unknown.…”

“…A previous study revealed that expression of miR-21 was induced by an increased level of TGF-β during smooth muscle cell development (15). Furthermore, Yu et al (8) demonstrated that TGF-β1 induced miR-21, which targeted the DNA damage sensors ATM serine/threonine kinase and mutS homolog 2 to regulate cancer responses to genotoxic chemotherapy (8). Therefore, the function of TGF-β1 in simulating miR-21 to promote metastasis and chemoresistance requires additional research.…”

Nuclear Translocation of Type I Transforming Growth Factor β Receptor Confers a Novel Function in RNA Processing

“…RNA extraction, reverse transcription (RT), and real-time quantitative PCR (qPCR) were performed as described previously (49). Primer sequences used were as follows: 5=-CC TGTTTCCTTGAGATCAGCTGC-3= and 5=-GTGAGGGAAGAAAGTT GGGAGCG-3= for the Chr7-6 T␤RI-binding site, 5=-CCCATAACCCCT GAGGGTAG-3= and 5=-CTCAGGCGGCAGTCATAGA-3= for the Chr7-193 T␤RI-binding site, 5=-GAGCCGCGAGAAGTGCTAGCTCG-3= and 5=-CTGGAGCACTGTCTGCGCACACC-3= for the Chr6-6 T␤RI-binding site, 5=-GGAAGTGTTGAAGGGAGGTGGCA-3= and 5=-CAAACCG TGCCTGGAAGTCAACG-3= for the Chr11-110 T␤RI-binding site, 5=-C ACTGCAGCACTTGAAGGAGG-3= and 5=-TGAGGCAGAGGCTGCCA TCTA-3= for the Chr15-7 T␤RI-binding site, 5=-TGGAGCCTCTTACAC CCAGT-3= and 5=-GCTTTCGGAGATGTTGCTTC-3= for human epidermal growth factor receptor (EGFR) isoform a, 5=-AACAACACCC TGGTCTGGAA-3= and 5=-TGAAGCAAAGGGAGAAATTGA-3= for human EGFR isoform b, 5=-GGATATTCTGAAAACCGTAAAGGAAA-3= and 5=-CGAAAAGTTCTCTCTAAAACACTGATT-3= for human EGFR isoform c, 5=-CCAGTGTGCCCACTACATTG-3= and 5=-CGCTGCCAT CATTACTTTGA-3= for human EGFR isoform d, 5=-GGCTCTGGAGGA AAAGAAAG-3= and 5=-CAATGAGGACATAACCAGCCAC-3= for all EGFR isoforms, 5=-GGCTCTGGAGGAAAAGAAAG-3= and 5=-AGAAC GAAACGTCCCGTTCCTC-3= for primary EGFR transcripts, and 5=-AC CACAGTCCATGCCATCAC-3= and 5=-TCCACCACCCTGTTGCTGT A-3= for human glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (as a control).…”

The Role of Epigenetic Modulation in the Cellular Response to Ionizing Radiation

“…The tumor suppressor p53 has a central role in the activation of genes in multiple pathways, including cellcycle regulation, tumor suppression, and apoptosis. miR-125b and miR-504 have been identified as negative regulators of p53 in several types of human cells [91,92] . Interestingly, miR-605, and miR-143/miR-145 are post-transcriptionally activated by p53 and, subsequently, target Mdm2, leading to rapid accumulation of p53 [93,94] .…”