Abstract P2-01-15: Inflammatory breast cancer cells are characterized by attenuated SMAD dependent TGFβ signaling leading to impaired cell motility responses

Abstract

Abstract Introduction.Inflammatory breast cancer (IBC) is an aggressive form of locally advanced breast cancer with elevated metastatic potential, characterized by the frequent presence of tumor emboli in dermal and parenchymal lymph vessels. In the past, evidence was provided that TGFβ signaling is part of the molecular biology of this disease. In this study, this relation was further examined. Materials and methods. TGFβ1 induced cell motility (i.e. XCELLigence, wound healing assays), gene expression (RNA-sequencing) and peptide phosphorylation (i.e. PAMGene technology) patterns were investigated in a panel of 3 IBC and 3 subtype-matched nIBC cell lines. In addition, a series of tissue samples from 75 and 135patients with and without IBC was investigated for nuclear expression of total SMAD2, SMAD3 and SMAD4 using immunohistochemistry. Finally, SMAD protein expression data were related to gene expression data from patients with available Affymetrix HGU133plus2 profiles. Results. The cell motility inducing capacity of TGFβ1 was strongly abrogated in all IBC cells independent of their molecular subtype (P=0.003). Genes differentially expressed between IBC and nIBC cells post 4 hours of TGFβ1 revealed attenuated expression of SMAD3 transcriptional regulators with concomitant overexpression of MYC target genes in IBC. Assessment of SMAD expression in patient samples demonstrated a near absence of nuclear SMAD3 expression in the primary tumors from patients with IBC (P<0.001) and a further reduction of SMAD3 staining intensity was observed in tumor emboli (P=0.019). Integrated analysis of gene and protein expression data revealed that a substantial fraction of the IBC signature genes correlated with SMAD3 and these genes (i.e. 21/24; P<0.001) carry evidence in favor of attenuated SMAD3 signaling in IBC. Discussion. It is demonstrated that IBC cells are characterized by attenuated SMAD3 protein expression and transcriptional activity that obliterates the cell motility inducing capacity of TGFβ1. Recent studies revealed that SMAD3 is essential for TGFβ1 induced cell motility through induction of epithelial to mesenchymal transition (EMT). In the absence of SMAD3 expression, a partial EMT is induced leading to collectively invading cancer cells that are gifted with a high metastatic potential and favor lymphatic dissemination, thereby providing an intriguing explanatory model of the biology of tumor emboli in IBC. Citation Format: Rypens C, Van Berckelaer C, Billet C, Hauspy J, Bertucci F, Peter V, Dirix L, Van Laere S. Inflammatory breast cancer cells are characterized by attenuated SMAD dependent TGFβ signaling leading to impaired cell motility responses [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-01-15.