Smad signaling is required to maintain epigenetic silencing during breast cancer progression.
Breast cancer progression is associated with aberrant DNA methylation and expression of genes that control the epithelial-mesenchymal transition (EMT), a critical step in malignant conversion. Although the genes affected have been studied, there is little understanding of how aberrant activation of the DNA methylation machinery itself occurs. Using a breast cancer cell-based model system, we found that cells that underwent EMT exhibited overactive transforming growth factor beta (TGFbeta) signaling and loss of expression of the CDH1, CGN, CLDN4, and KLK10 genes as a result of hypermethylation of their corresponding promoter regions. Based on these observations, we hypothesized that activated TGFbeta-Smad signaling provides an "epigenetic memory" to maintain silencing of critical genes. In support of this hypothesis, disrupting Smad signaling in mesenchymal breast cancer cells resulted in DNA demethylation and reexpression of the genes identified. This epigenetic reversal was accompanied by an acquisition of epithelial morphology and a suppression of invasive properties. Notably, disrupting TGFbeta signaling decreased the DNA binding activity of DNA methyltransferase DNMT1, suggesting that failure to maintain methylation of newly synthesized DNA was the likely cause of DNA demethylation. Together, our findings reveal a hyperactive TGFbeta-TGFbetaR-Smad2 signaling axis needed to maintain epigenetic silencing of critical EMT genes and breast cancer progression.
Papageorgis
Panagiotis
P
Departments of Medicine (Genetics and Molecular Medicine Programs and Cancer Research Center), Genetics and Genomics, Boston University School of Medicine, Boston, Massachusetts, USA.
Lambert
Arthur W
AW
Ozturk
Sait
S
Gao
Fangming
F
Pan
Hongjie
H
Manne
Upender
U
Alekseyev
Yuriy O
YO
Thiagalingam
Arunthathi
A
Abdolmaleky
Hamid M
HM
Lenburg
Marc
M
Thiagalingam
Sam
S
D015703:Antigens, CD; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D062506:Claudin-4; D016000:Cluster Analysis; D019175:DNA Methylation; D018450:Disease Progression; D044127:Epigenesis, Genetic; D004848:Epithelium / Q000378:metabolism / Q000473:pathology; D020869:Gene Expression Profiling; D006801:Humans; D007610:Kallikreins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism / Q000473:pathology; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism*; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism; D051906:Smad7 Protein / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism
D015703:Antigens, CD; C513384:CDH1 protein, human; C061407:CGN protein, human; C568157:CLDN4 protein, human; D015820:Cadherins; D062506:Claudin-4; D008565:Membrane Proteins; D008840:Microfilament Proteins; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D051899:Smad2 Protein; D051906:Smad7 Protein; D053773:Transforming Growth Factor beta1; C100936:KLK10 protein, human; D007610:Kallikreins