Abstract 168: Transglutaminase 2 (TGM2) overexpression contributes to triple-negative breast cancer metastasis through AFAP1-dependent pathway
Authors: Piacsek Mitchell , Sand Andrea , Rovin Richard A. , Bosenko Dmitry , Konduri Santhi D. , Tjoe Judy A. , Yin Jun 
Published: August 2019

Abstract
Triple-Negative Breast Cancer (TNBC) is a type of breast cancer with absence of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). It represents 10-20% of all breast cancer cases, and is associated with frequent relapse and poor prognosis due to the lack of targeted therapy. Amongst all TNBC, metastatic TNBC is associated with the worse prognosis and has the fewest therapeutic options. Therefore, identifying molecular drivers for TNBC metastasis and developing potential targeted therapies will be highly beneficial for patients with metastatic TNBC.
We classified 8 TNBC cell lines into two groups, more invasive (n = 3) vs. less invasive (n = 5), by assessing their abilities to both invade through 3D Matrigel and migrate distantly, characterized through in vitro cell invasion and migration assays, respectively. We compared the two groups using transcriptome profiles from Cancer Cell Line Encyclopedia (CCLE) and found that transglutaminase 2 (TGM2) was significantly upregulated in more invasive cell lines (fold change = 4.6, p &lt; 0.001). Overexpression of TGM2 at both RNA and protein levels was confirmed experimentally in more invasive TNBC cells. These findings indicated that TGM2 might play a role in TNBC metastasis, but its functionality in invasiveness has not been evaluated by previous studies. In our study, suppressing TGM2 expression either by TGM2 inhibitor, cystamine dihydrochloride (CD), or by silencing TGM2 (siRNA) was found to significantly reduce the amount of invaded cells and inhibit cell migration, suggesting that TGM2 contributes to both cell invasion and cell migration in TNBC.
Our analysis also showed a significant correlation (r = 0.94, p = 0.001) between expression levels of TGM2 and actin filament-associated protein 1 (AFAP-1). AFAP1, which regulates actin cytoskeleton integrity and was found to contribute to tumorigenic growth by regulating focal contacts in other cancer types, was suppressed when TGM2 expression was downregulated, suggesting that TGM2 may potentiate cell metastasis through upregulation of AFAP-1 expression in TNBC. We also observed co-localization of AFAP-1 and actin filaments and that downregulation of TGM2 dramatically reduced actin filament assembly.
These observations identify a novel role of TGM2 in promoting TNBC cell metastasis and a new machinery of TGM2 in regulating microfilaments through AFAP-1. To conclude, TGM2 could act as a powerful biomarker and a molecular target circumventing TNBC metastasis. (Judy A. Tjoe and Jun Yin are considered to be co-corresponding authors for this study)
Citation Format: Mitchell Piacsek, Andrea Sand, Richard A. Rovin, Dmitry Bosenko, Santhi D. Konduri, Judy A. Tjoe, Jun Yin. Transglutaminase 2 (TGM2) overexpression contributes to triple-negative breast cancer metastasis through AFAP1-dependent pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 168.