TBX2 interacts with heterochromatin protein 1 to recruit a novel repression complex to EGR1-targeted promoters to drive the proliferation of breast cancer cells

Abstract

Early Growth Response 1 (EGR1) is a stress response transcription factor with multiple tumour suppressor roles in breast tissue, whose expression is often lost in breast cancers. We have previously shown that the breast cancer oncogene TBX2 (T-BOX2) interacts with EGR1 to co-repress EGR1-target genes including the breast tumour suppressor NDRG1. Here, we show the mechanistic basis of this TBX2 repression complex. We show that siRNA knockdown of TBX2, EGR1, Heterochromatin Protein 1 (HP1) isoforms and the generic HP1-associated corepressor protein KAP1 all resulted in growth inhibition of TBX2-expressing breast cancer cells. We show that TBX2 interacts with HP1 through a conserved HP1-binding motif in its N-terminus, which in turn leads to the recruitment of KAP1 and other associated proteins. Mutation of the TBX2 HP1 binding domain abrogates the TBX2-HP1 interaction and loss of repression of target genes such as NDRG1. Chromatin-immunoprecipitation (ChIP) assays showed that TBX2 establishes a repressive chromatin mark, specifically H3K9me3, around the NDRG1 proximal promoter coincident with the recruitment of the DNA methyltransferase DNMT3B and histone methyltransferase (HMT) complex components (G9A, Enhancer of Zeste 2 (EZH2) and Suppressor of Zeste 12 (SUZ12)). Knockdown of G9A, EZH2 or SUZ12 resulted in upregulation of TBX2/EGR1 co-regulated targets accompanied by a dramatic inhibition of cell proliferation. We show that a generic inhibitor of HMT activity, DzNep, phenocopies expression of an inducible dominant negative TBX2. Knockdown of TBX2, KAP1 or HP1 inhibited NDRG1 promoter decoration specifically with the H3K9me3 repression mark. Correspondingly, treatment with a G9A inhibitor effectively reversed TBX2 repression of NDRG1 and synergistically downregulated cell proliferation following TBX2 functional inhibition. These data demonstrate that TBX2 promotes suppression of normal growth control mechanisms through recruitment of a large repression complex to EGR1-responsive promoters leading to the uncontrolled proliferation of breast cancer cells.

The Role of Early Growth Response 1 in the Prognostic Value and Cell Migration of Breast Cancer

“…The high expression of EGR1 exhibited a correlation with ne RFS. Crawford et al found the expression of EGR1 was reduced in BRCA, which was in agreement with our results [28]. Besides, active EGR1 elevated PAC1 expression with excessive oxygen species, ultimately causing the chromatin remodeling mechanism of effector T cells [29].…”

A Risk Prediction Model for Breast Cancer Based on Immune Genes Related to Early Growth Response Proteins Family

“…As previously reported, EGR1 plays multiple tumor suppressor roles in breast cancer, in which its expression is often lost ( Crawford et al, 2019 ); EGR2 is a growth inhibitor when upregulated in tumor cells ( Salotti et al, 2015 ), exogenous expression of EGR2 can also suppress the growth of tumor cells ( Unoki and Nakamura, 2003 ), but its role in breast cancer is rarely reported; downregulation of EGR3 can promote the migration and invasion of hepatocellular carcinoma (HCC) ( Wangdong et al, 2017 ), high expression level of EGR3 was discovered in prostate cancer samples ( Pio et al, 2013 ), but its role in breast cancer is also rarely reported. Few researches reported EGR4 in malignant tumors; only some articles reported that EGR4 might promote NSCLC ( He et al, 2019 ), small cell lung cancer (SCLC) ( Matsuo et al, 2014 ), and cholangiocarcinoma (CHOL) to develop ( Gong et al, 2020 ).…”

T-Box Transcription Factor 22 Is an Immune Microenvironment-Related Biomarker Associated With the BRAFV600E Mutation in Papillary Thyroid Carcinoma

“…Recently, accumulating studies show that certain T-box genes also play an important role in cancer progression. Upregulated TBX2 and TBX3 promoted tumorigenesis and progression of different types of cancer (Durbin et al, 2018;Crawford et al, 2019;Krstic et al, 2019). In contrast, a recent study revealed that TBX1 functions as a tumor suppressor in PTC (Wang et al, 2019).…”

“…Previous studies had demonstrated that mutations in different members of the T-box family result in developmental syndromes, characterized by organ deformity and body structure defects (Miller et al, 2010). In recent years, increasing studies reported that the T-box genes might also function in tumorigenesis and progression in certain cancers (Crawford et al, 2019;Krstic et al, 2019). As a member of the T-box gene family, T-box transcription factor 22 (TBX22) mutations caused a high risk of incidence in several diseases, including non-syndromic cleft palate, hypodontia, and ankyloglossia (Braybrook et al, 2001;Kantaputra et al, 2011).…”