cancers Article HMGA2 Supports Cancer Hallmarks in Triple-Negative Breast Cancer Behzad Mansoori 1,2,3 , Mikkel Green Terp 2 , Ali Mohammadi 2 , Christina Bøg Pedersen 2 , Henrik Jørn Ditzel 2,4,5 , Behzad Baradaran 1 and Morten Frier Gjerstorff 2,4,5, *   Citation: Mansoori, B.; Terp, M.G.; Mohammadi, A.; Pedersen, C.B.; Ditzel, H.J.; Baradaran, B.; Gjerstorff, M.F. HMGA2 Supports Cancer Hallmarks in Triple-Negative Breast Cancer. Cancers 2021, 13, 5197. https://doi.org/10.3390/cancers 13205197 Academic Editors: Paola Marcato and Maurizio Di Bonito Received: 3 October 2021 Accepted: 11 October 2021 Published: 16 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Immunology Research Center, Tabriz University of Medical Sciences, Golghasht St., Tabriz 51666-14731, Iran; b.mansoori_lab@yahoo.com (B.M.); baradaranb@tbzmed.ac.ir (B.B.) 2 Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, J. B. Winsløws Vej 25, 3, DK-5000 Odense C, Denmark; mterp@health.sdu.dk (M.G.T.); amohammadi@health.sdu.dk (A.M.); cbpedersen@health.sdu.dk (C.B.P.); hditzel@health.sdu.dk (H.J.D.) 3 Aging Research Institute, Physical Medicine and Rehabilitation Research Center, Tabriz University of Medical Sciences, Golghasht St., Tabriz 51656-65811, Iran 4 Department of Oncology, Odense University Hospital, DK-5000 Odense C, Denmark 5 Academy of Geriatric Cancer Research (AgeCare), Odense University Hospital, DK-5000 Odense C, Denmark * Correspondence: mgjerstorff@health.sdu.dk; Tel.: +45-2126-1563; Fax: +45-6550-3922 Simple Summary: Triple-negative breast cancer grows and spreads faster compared to other types of invasive breast cancer and has limited treatment options and subsequently worse prognosis. High mobility group A 2 (HMGA2) protein is widely expressed in undifferentiated cells including cancer cells. HMGA2 is a DNA binding protein involved in DNA architecture and the functional regulation of DNA. It was reported that HMGA2 is aberrantly regulated malignant signaling in different types of cancers. In this study, we aim to reveal the role of HMGA2 in TNBC biology and demonstrate a link between HMGA2-mediated cancer phenotypes and the regulation of NF-kB/IL-6/STAT3 signaling. Abstract: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that exhibits a high proliferation rate and early metastasis leading to a poor prognosis. HMGA2 is a DNA binding transcriptional regulator implicated in tumorigenesis. Here, we demonstrate that the HMGA2 promoter is demethylated in TNBC tumors, leading to increased expression of HMGA2 at both mRNA and protein levels. Importantly, high HMGA2 levels in TNBC tumors are correlated with poor prognosis. To detail the role of HMGA2 in TNBC development and progression, we studied its effect on core cancer phenotypes. Stable knockdown of HMGA2 in TNBC cells revealed that HMGA2 may support cell proliferation, cell migration and invasion. In addition, HMGA2 knockdown decreased cancer stem cell (CSC) features. Importantly, we found that silencing HMGA2 inhibited NF-kB signaling and lead to decreased expression of the downstream molecules IL-6 and IL-8 and reduced STAT3 pathway activation. Our results demonstrate that HMGA2 supports cancer hallmarks in TNBC and may represent a promising target for TNBC treatment. Keywords: HMGA2; triple-negative breast cancer; NF-kB; IL-6; IL-8; STAT3 1. Introduction According to WHO, breast cancer is the most common cancer and the second leading cause of death in women. Based on molecular profiling, breast cancer is divided into five subtypes, i.e., normal breast-like, luminal A, luminal B, HER2-enriched, and triple-negative, each of which have a very different prognosis and treatment options [1]. Of those diagnosed with breast cancer, 15–20% are classified as triple-negative breast cancer (TNBC) [2], which is identified by the absence of an estrogen receptor (ER) and a progesterone receptor (PR) and does not make too much of epidermal growth factor receptor type 2 (Erbb2/HER2) [3]. TNBC is generally very aggressive, with a high proliferation rate and early metastasis, leading to a poor prognosis [4]. Cancers 2021, 13, 5197. https://doi.org/10.3390/cancers13205197 https://www.mdpi.com/journal/cancers