Silencing of the Tropomyosin-1 gene by DNA methylation alters tumor suppressor function of TGF-beta.
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.
Varga
Andrea E
AE
Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Stourman
Nina V
NV
Zheng
Qiao
Q
Safina
Alfiya F
AF
Quan
Lei
L
Li
Xiurong
X
Sossey-Alaoui
Khalid
K
Bakin
Andrei V
AV
D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D001483:Base Sequence; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D019175:DNA Methylation; D000077209:Decitabine; D005091:Exons / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D006801:Humans; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D009362:Neoplasm Metastasis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000502:physiology; D014335:Tropomyosin / Q000235:genetics*
D012333:RNA, Messenger; C490775:TPM1 protein, human; D016212:Transforming Growth Factor beta; D014335:Tropomyosin; D000077209:Decitabine; D001374:Azacitidine