Abstract

Introduction: Transforming growth factor-β (TGF-β) is known to play significant dual roles in cell development and pathophysiology but very cell-specific dependent. Due to these features, it has been concomitantly associated in the development of triple negative breast cancer (TNBC) via activation of TGF-β signaling pathway. In house baseline studies directed the involvement of TGF-β signaling in TNBC via differentially expression analyses and may be regulated by SETDIA, an epigenetic regulator. This study aimed to identify differentially expressed genes by SETD1A knockdown and elucidate the molecular mechanism of TGF-β signaling across isoforms. Methods: Two TNBC cell line models (FEC-sensitive MDA-MB-468 and FEC-resistant Hs578T; FEC – 5-flurouracil, epirubicin, cyclophosphamide chemo cocktail) were transfected by SETDIA siRNA and RNA were subjected for the Nanostring Cancer Progression Panel. Differentially expressed mRNA and pathway analysis were performed using the nSolver Software. RqPCR were carried out to confirm downstream regulated genes. Wound scratch, colony forming, invasion assays were conducted to complement the gene mechanisms. Results: Differentially expressed genes (TGF-β1, SMAD1, ID2, ZEB1) narrowed down TGF-β signaling among top hit pathways. Each gene was found to be differentially expressed between the MDA-MB-468 and Hs578T cell lines. TGF-β1, TGF-β3, SMAD1, SMAD2 and ID2 genes were upregulated and TGF-β2 was suppressed by SETD1A knockdown in FEC-resistant TNBC (Hs578T). These genes were inversely expressed in MDA-MB-468 cell line. SETD1A knockdown inhibited proliferative effects in TNBC cell lines, complemented by downregulation of Ki-67 by colony forming assay. Reduction wound closure were observed upon SETD1A knockdown. Induction of invasion were seen in TGF-β2 and TGF-β3 in a recovery setup. Conclusion: TGF-β signaling maybe a key regulator of TNBC development via activation of epigenetic regulator SETD1A. TNBC may be regulated via intrinsic mechanisms differing between FEC-sensitive and FEC-resistant cells, indicating a potential personalised therapeutic intervention in the two intrinsic TNBC groups. However, further evaluation is warranted to extend the understanding of TNBC progression by TGF-β signaling activation. 

Keywords: TNBC, TGF-β, SETD1A, Chemoresistance, Epithelial-Mesenchymal-Transition, Triple negative breast cancer