Silencing of the Tropomyosin-1 gene by DNA methylation alters tumor suppressor function of TGF-β

• Published in: Oncogene Vol. 24; no. 32; pp. 5043 - 5052
• Main Authors: VARGA, Andrea E, STOURMAN, Nina V, QIAO ZHENG, SAFINA, Alfiya F, LEI QUAN, XIURONG LI, SOSSEY-ALAOUI, Khalid, BAKIN, Andrei V
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing 28.07.2005; Nature Publishing Group
• Subjects: Actin; Azacitidine - analogs & derivatives; Azacitidine - pharmacology; Azacytidine; Base Sequence; Biological and medical sciences; Bisulfite; Breast Neoplasms; Cell adhesion & migration; Cell Line, Tumor; Cell migration; Cell physiology; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; CpG islands; Cytosine; DNA Methylation; Epigenetics; Epithelial cells; Exons - genetics; Female; Fibers; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Neoplastic - drug effects; Gene Silencing; Genes, Tumor Suppressor; Humans; Introns - genetics; Metastases; Metastasis; Molecular and cellular biology; Molecular Sequence Data; Molecular weight; Neoplasm Metastasis; Promoter Regions, Genetic; RNA, Messenger - drug effects; RNA, Messenger - genetics; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - physiology; Transforming growth factor-b; Tropomyosin; Tropomyosin - genetics; Tumor cell lines; Tumor cells; Tumor suppressor genes; Smad protein; Transforming growth factor β; Tropomyosin; DNA; DNA methylation; TGF-β; Smad; Malignant tumor; Metastasis; Methylation; Carcinogenesis; Tumor suppressor gene
• DOI: 10.1038/sj.onc.1208688
• ISSN: 0950-9232

Loss of actin stress fibers has been associated with cell transformation and metastasis. TGF-beta induction of stress fibers in epithelial cells requires high molecular weight tropomyosins encoded by TPM1 and TPM2 genes. Here, we investigated the mechanism underlying the failure of TGF-beta to induce stress fibers and inhibit cell migration in metastatic cells. RT-PCR analysis in carcinoma cell lines revealed a significant reduction in TPM1 transcripts in metastatic MDA-MB-231, MDA-MB-435 and SW620 cell lines. Treatment of these cells with demethylating agent 5-aza-2'-deoxycytidine (5-aza-dC) increased mRNA levels of TPM1 with no effect on TPM2. Importantly, 5-aza-dC treatment of MDA-MB-231 cells restored TGF-beta induction of TPM1 and formation of stress fibers. Forced expression of TPM1 by using Tet-Off system increased stress fibers in MDA-MB-231 cells and reduced cell migration. A potential CpG island spanning the TPM1 proximal promoter, exon 1, and the beginning of intron 1 was identified. Bisulfite sequencing showed significant cytosine methylation in metastatic cell lines that correlated with a reduced expression of TPM1. Together these results suggest that epigenetic suppression of TPM1 may alter TGF-beta tumor suppressor function and contribute to metastatic properties of tumor cells.