Breast cancer (BC) is the most commonly occurring invasive cancer in women worldwide and the second leading cause of cancer-related deaths in women after lung cancer. Although the overall methods for screening, diagnosis, and treatment of BC have improved in recent years, prognosis remains poor (1). More than one million new cases of BC are reported per year, and the risk of an individual dying from this life-threatening disease is 1/35 (2). Therefore, the identification of more effect-ive and specific biomarkers for the prognosis of BC patients is of paramount importance. The development of BC is usually attributed to multi-gene mutations (3). Molecular targeted treatments have recently transformed the therapeutic approach for various tumors. To adopt a targeted therapy for the treatment of BC patients, it is critical to better understand the status of various molecular processes, such as gene expression and methylation of the related genes.
The early growth response 1 (
We performed a PubMed and Scopus literature search until June 2021 using keywords: EGR1 and cancer/breast cancer (BC), signaling pathway, treatment, and therapeutics. In this review, we included English language articles focused on EGR1-related BC progression and prognosis, and its therapeutic applications.
TCGA data regarding
TCGA data regarding
EGR1 protein expression in BC and its normal tissue was analyzed by immunohistochemistry (IHC). The tissue images were downloaded from the human protein atlas web (https://www.proteinatlas.org/; accessed January 2021) (26, 27). The antibody (CAB019427) against EGR1was used for IHC analysis. The intensity of EGR1 expression was measured using ImageJ following Crowe
Median methylation level of the
The Catalog of Somatic Mutations in Cancer (COSMIC) web resource (https://cancer.sanger.ac.uk/cosmic) (31) was used to analyze EGR1 protein somatic mutations in human cancer. A pie-chart was constructed showing the percentage of different EGR1 mutation types in BC. The cBioPortal web tool (http://www.cbioportal.org/; accessed July 2020) (32, 33) was also used to analyze the frequency of mutations and their location in the EGR1 protein in BC.
Survival analysis of BC patients with high or low
The co-expression of
Co-expression between EGR1 or other genes was analyzed and displayed using bcGenExMiner v4.1 (http://bcgenex.centregauducheau.fr/BC-GEM/GEM-Accueil.php?js=1 accessed January 2021) (37). Statistical analysis was performed using a Welch’s test with a Dunnett-Tukey-Kramer’s test and P < 0.05 was considered significant.
The EGR1 protein contains 543 amino acids in humans, consisting of three Cysteine 2-Histidine 2 (C2H2) zinc fingers DNA-binding domains (Fig. 1A) (38). It also contains a strong activation domain, repressor domain (also known as NAB binding site), a nuclear localization domain, and a weak activation domain. Protein kinases and phosphatases controls the phosphorylation of the different EGR1 domains (39). The protein activates or represses specific genetic programs based on its “phosphorylation/acetylation pattern”. The T309 and S350 sites are phosphorylated by protein kinase B (PKB, alias AKT); whereas S378, T391, and T526 sites are phosphorylated by casein kinase II (38). Depending on its post-translational modification statues, EGR1 shows various transcriptional activation or repression functions. SUMO1 can be responsible for SUMOylation of EGR1 at K272. Also, the inhibition of Egr1 transcriptional activity can be triggered by transcriptional co-repressors NGFI-A binding proteins NAB1 and NAB2 via binding to the repressor domain.
EGR1 plays a significant role in the growth, proliferation, and differentiation of various types of cells (40, 41). Although the detailed mechanisms are not yet well characterized, EGR1 plays diverse biological roles in cell signaling. High expression of EGR1 is involved in the acute phase of IL-4 transcription elevation in response to T cell receptor stimulation (40). Duclot and Kabbaj reviewed that EGR1 also regulates brain plasticity and neuropsychiatric disorders (42). Overexpression of EGR1 induced synaptic plasticity, wound repair, female reproductive capacity, and apoptosis by upregulating downstream genes (43). Several studies have shown that up-regulation of EGR1 contributes to the suppression of various human cancers progression except for prostate and bladder cancers (11, 12, 15, 44, 45). In addition, a study has claimed that knockdown of EGR1 could inhibit prostate cancer invasion by attenuating IL-8 production, while another study revealed nanotechnology-based EGR1-assisted targeted therapies for preventing cancer development (46, 47). However, the prognostic significance of EGR1 varies depending upon the cancer type. For example, EGR1 is considered oncogenic in prostate cancer (48, 49), whereas it is usually regarded as a tumor suppressor in BC (16, 17). Moreover, the diverse roles of EGR1 expression in the growth and metastasis of particular cancer remain largely unknown.
To investigate the expression level of
The analysis on EGR1 transcript expression reported in the preceding section considered the entire expression data for all BC subtypes combined. In clinical practice, however, subtypes of BC may be advantageous in planning overall treatment and developing precise therapies. Here, we therefore aimed to explore the relationship of
As presented in Fig. 1E-G, we performed a number of between-class mRNA expression comparisons, including both molecular and clinical subtypes using TCGA data through the UCSC Xena web. In PAM50 molecular subtypes, the lowest level of
Epigenetic alterations in cancers can regulate gene expression. This regulation depends on the methylation on the gene promoter regions, which subsequently regulate the gene transcription. Hypermethylation on gene promoter prevents the transcription factor binding on the promoter, which eventually inhibits the gene’s transcription. It is previously reported that epigenetic alteration on gene promoter modulates the gene transcription and thus regulates carcinogenesis (52-54). Therefore, we investigated the methylation status of the
We then focused on the mutations and copy number alterations (CNAs) of EGR1 in BC. Somatic cells can be mutated spontaneously throughout a person’s lifetime. We analyzed somatic mutations in EGR1 in BC using COSMIC. The results of the different types of mutations are presented in Fig. 2B. Of the queried samples, 9 samples were associated with somatic mutations. Most of the somatic mutations cannot show any obvious effect, while few of them can change the key molecular functions in cancer cells (55). The major mutation types were synonymous substitution, missense substitution, frameshift insertion, and nonsense substitution, with rates of 33.33%, 33.33%, 22.22%, and 11.11% of the mutant samples, respectively (Fig. 2B). Of the EGR1 mutations detected in BC tissues, 42.86% were G>C mutations (Fig. 2B). Moreover, we determined the EGR1 mutation frequency in BC using cBioPortal. These results showed that BRCA (INSERM 2016) had the most genetic alterations, accounting for approximately 1% of all samples (Fig. 2C). The mutation sites for EGR1 in BC tissues were located between amino acids 0 and 543, with a hotspot at H334Pfs*13, suggesting that mutations in
We next investigated whether
In this study, we used various web-based bioinformatics tools to perform a multiomics analysis of
The data that support the findings of this study are available from the corresponding author upon reasonable request.
This study was supported by grants from the National Research Foundation (NRF) funded by the Korean government (grant no. 2015R1A5A1009701 and 2019M3A9H1030682); and, in part by the National Research Foundation of Korea-Grant funded by the Korean Government (Ministry of Science and ICT)-NRF-2017R1A2B2012337. In addition, this paper was written as part of Konkuk University's research support program for its faculty on sabbatical leave in 2019-2020.
The authors have no conflicting interests. The sponsors had no role in the design, execution, interpretation, or writing of the study.