Accommodating Consciousness: How Should we Conceptualize the Mind in a Physical Reality?
The Role of Inherited BRCA1 Mutations in Triple-Negative Breast Cancer:
An Analysis of the Expression Mechanisms of Estrogen, Progesterone, and
Epidermal Growth Factor 2 Receptors Concerning BRCA1 Mutations
Marianny Zavala
Lone Star College
Abstract
With an aim to elucidate the effect of BRCA1 in Triple Negative Breast Cancer (TNBC), this study analyzed the BRCA1 regulatory role at the centromere and its impact on the expression regulation mechanisms of Estrogen (ER), Progesterone (PR), and Human Epidermal Growth Factor 2 (HER2) receptors. First, Suba’s (2015) BRCA1 and ER-alpha expression mechanism model was selected to serve as the foundation for this study. According to Suba, mutual regulatory mechanisms take place during normal and abnormal cell proliferation between BRCA1 and ER-alpha. Suba’s model is paired with Iqbal and Iqbal’s (2014) research to illustrate estrogen’s ability to activate HER2 signaling through ER’s non-genomic activity.
Second, research by Di Paolo et al. (2014) focused on centromeric cohesion, and chromosomal instability stating that the loss of BRCA1 genes causes centromere amplification and chromosomal missegregation. Third, Halilovic et al. (2019) research further suggests a correlation between HER2-negative status and chromosomal instability as a result of BRCA1gene loss. A comparative analysis of these four studies suggest that the loss, or dysfunction, of BRCA1 significantly affects receptors involved in TNBC, therefore slowing down or completely eliminating their expression mechanisms. These results suggest opportunities to improve treatment options and reduce mortality rates for individuals diagnosed with TNBC and other receptor-negative cancers. Future research could explore PR’s signaling patterns in conjunction with ER and BRCA1, as well as the potential impact of mutated BRCA1 genes on other genes associated with receptor regulation.
Introduction
Recent studies suggest women who inherit BRCA1 mutated genes have an increased risk of developing breast cancer before age 50 by 60% to 85%. Breast Cancer 1 (BRCA1) and Breast Cancer 2 (BRCA2) genes are tumor suppressant genes responsible for producing BRCA1 and BRCA2 proteins. These proteins are crucial in limiting rapid tissue cell growth (Casaubon et al.,2023), and precisely repairing damaged DNA through homologous recombination (Gorodetska 2019). Mutations in any of these genes increase the likelihood of developing breast cancer between 40% and 80%, in addition to a higher chance of developing ovarian, pancreatic, and prostate cancers (Casaubon et al., 2023).
Inherited BRCA1 mutations frequently develop Triple-Negative Breast Cancer (TNBC), an aggressive subtype of basal-like breast cancer, characterized by the absence of Estrogen Receptor (ER), Progesterone Receptor (PR), and Human Epidermal Growth Factor Receptor 2
(HER2) expression (Davaadelger et al., 2019). Due to the lack of these receptors, TNBC results in a more aggressive course and worse prognosis, with a mortality rate of 40% within 5 years of diagnosis (Yin et al., 2020). It is also highly invasive, and even with proper treatment, 46% of TNBC patients develop distant metastasis, with a recurrent rate after surgery of 25%, and a median survival time of 13 months (Yin et al., 2020). While TNBC accounts for 15% of breast cancers, it is responsible for 50% of breast cancer mortality, and its poor prognostic leaves patients with little hope after diagnosis due to its complex interplay of pathways (Treeck et al.,2020). This research contributes valuable insights to enhance the understanding of TNBC’s aggressive nature and it has the potential to ultimately improve treatment options and outcomes in order to reduce mortality rates.
Although research has been done on the relationship between BRCA1 and ER, PR, and HER2 in order to find alternative effective treatments, little progress has been made due to the complex relationship between BRCA1 and the receptors’ expression regulation mechanisms.With an aim to understand the complex relationship between BRCA1 and its receptors in Triple Negative Breast Cancer, this study analyzes the BRCA1 centromere regulatory role and how it affects the expression regulation mechanisms of ER, PR, and HER2. This paper investigates the interplay of pathways between BRCA1 and its receptors and elucidates BRCA1's role in centromere regulation. An analysis of the regulatory mechanisms between the BRCA1 gene and the receptors reveals how ER and BRCA1 mutually regulate their expression mechanisms, and how ER can activate HER2 signaling through non-genomic activity.
BRCA1 Receptors
Chromosome 17 Centromere
Chromosome 17 is the second chromosome with the highest gene density in the human genome (Zody et al., 2006). A variety of famous oncogenes and tumor suppressant genes such as BRCA1, HER2, p53, TOP2A, and HIC-1 are located in this chromosome (Halilovic et al., 2019). Due to the high density of these oncogenes and tumor suppressor genes, mutations in this chromosome have been found in several types of cancer, including breast cancer (Medline, n.d.). Centromeres are regions in chromosomes responsible for ensuring correct chromosome segregation during cell division. An abnormal increase in the expression of centromeric proteins or DNA in this region is known as centromere overexpression, which can lead to chromosomal instability (CIN). CIN occurs when the rate of missegregation of whole or partial chromosomes is persistently high during the cell cycle, this could be due to defective regulators, resulting in overexpression or aneuploidy. Centromere duplication regulators, such as Aurora A and PLK1, are often dysregulated in breast cancer, and correlations have been found between the upregulation of centromere regulators and resistance to chemotherapy (Yoshino et al., 2021). According to various studies, up to 68% of breast carcinomas exhibit chromosome 17 centromere mutation (Halilovic et al., 2019). The data implies that the poor prognosis for TNBC and other cancer patients could be a result of CIN induced by centromere mutations.
The Role of BRCA1 in Centrosome Regulation
As previously mentioned, the BRCA1 protein has multiple functions, including DNA repair, cell cycle regulation, chromatin remodeling, and transcription regulation. It can also interact with other proteins and aid as a chromatin structure regulator. Centromere mutations are more common in TNBC than in any other cancer subtype (Yoshino et al., 2021). Research has found that the loss or deficiency of BRCA1 genes results in centromere amplification and chromosomal missegregation in mammary epithelial cells (Di Paolo et al., 2014). In BRCA1- deficient cells CpG methylation (DNMT3b) binding ability to satellite sequences is reduced– DNMT3b establishes DNA methylation patterns to recruit proteins involved in gene expression; they present inadequate centromere cohesion, as well as inhibition of centromeric Aurora B recruitment and activity (Di Paolo et al., 2014). These issues can lead to chromosomal missegregation, as mentioned before, as well as merotelic attachments, the attachment of a chromatid to multiples or opposite spindle fibers.
Relationship Between HER2 Status and Centromere Amplification
HER2 is also located in chromosome 17, specifically on q12-21.32, next to the centromere. Research has shown that of 75 HER2-negative cancer patients, 54.7% also presented aneuploid with gain (Halilovic et al., 2019), suggesting a correlation between HER2- negative status and chromosome 17 polysomy, especially considering how close it is to the centromere and the percentage of cancer patients who exhibit chromosome 17 centromere with gains. Researchers have found no direct correlation between HER2-negative status and centromere amplification, yet multiple studies support a co-correlation between HER2 amplification and overexpression and centromere with gains. As aforementioned, CIN can result in overexpression or aneuploidy. It is possible for the overexpression to affect the inherited mutated BRCA1 gene and cause the overproduction of more deficient BRCA1 protein. Since HER2 is also located in chromosome 17, overexpression of deficient BRCA1 protein can also affect it, however, co-correlations between the centromere overexpression and HER2 gene amplification have further scientific backing. The amplification of HER2 is highly associated with a positive HER2 status, contrary to the negative HER2 status of TNBC. Further research is required in order to understand the relationship between HER2- negative and centromere amplification.
The Role of BRCA1 in Estrogen Receptor Alpha Expression
Estrogen is a well-known human carcinogen and plays a crucial role in cancer cell proliferation in estrogen-dependent cancers. However, in ER-negative breast cancers, the cancer cells lack estrogen receptors, therefore estrogen does not have a direct role in promoting malignant cell proliferation. Despite estrogen not playing an active role in promoting cell proliferation in estrogen-independent cancers, the lack of estrogen in the cells makes them less responsive to hormone therapies targeting estrogen, as well as producing more aggressive breast cancers. (Chen and Li, 2022).
Because of its significant role in breast cancer, extensive research has been done on the interplay between ER-alpha and BRCA1 to better understand the expression mechanisms of both. Research strongly suggests that a deficient BRCA1 gene or the loss of this gene can affect the expression and proliferation effects of estrogen and estrogen receptors (Suba, 2015). It was also found that BRCA1 overexpression inhibits the expression of most estrogen-inducible genes (Katiyar et al., 2006), suggesting that BRCA1 possesses an inhibitory effect on estrogen receptors by influencing ER signaling pathways (Wang et al., 2018). Studies support the mutual regulations between BRCA1 and ER-alpha expressions during cell proliferation. As noted in the outer circle of Figure 1, during normal cell proliferation, the BRCA1 protein binds to Estrogen Receptor 1 (ESR1)– the coding protein gene for ER-alpha– promoting the expression of this gene. Estrogen will then bind to ER-alpha. Bounded ER-alpha and estrogen together bind to the BRCA1 promoter, stimulating BRCA1 mRNA and protein expression. This complex interplay between BRCA1 and ER-alpha illustrates the dynamic regulatory relationship extends beyond normal cell proliferation, also taking place during malignant cell proliferation (Suba, 2015).
As noted in the inner circle of Figure 1, in BRCA1-mutated cells the regulatory process is significantly reduced and/or stopped. During cell proliferation in these cells, the BRCA1 gene fails to produce or produces deficient BRCA1 protein, the protein is unable to properly bind to ESR1, therefore repressing the expression of ER-alpha mRNA and protein. Less estrogen binds to the ER-alpha due to the low amount of ER-alpha present in the cell. Consequently, low to no bounded estrogen and ER-alpha will bind to the BRCA1 promoter, downregulating BRCA1 mRNA and protein expression (Suba, 2015). Mutations in the BRCA1 gene actively interact with ERS1 and ER-alpha, therefore downregulating or repressing ER-alpha mRNA and protein expression. This correlates with previous mentions stating that BRCA1 mutation carriers frequently develop TNBC or ER-negative cancers.
Figure 1. Co-regulation between BRCA1 and ER-alpha Expression
Note. From “DNA stabilization by the upregulation of estrogen signaling in BRCA gene mutation carriers” by Z. Suba, 2015, Drug design, development and therapy, 9, p. 2665. The outer circle represents the normal functioning of the co-regulation between BRCA1 and ER-alpha during cell proliferation. The inner circle represents the same regulatory cycle with deficient BRCA1 and/or ER-alpha protein expression during malignant cell proliferation.
Relationship Between HER2 and Estrogen Receptors
HER2 forms part of the Epidermal Growth Factor Receptor (EGFR) family. It is different from other members of the EGFR family because it is unable to bind with EGF-link ligands for activation, instead, it relies on heterodimerization with other members of the EGFR family. Due to the ErbB proteins' complex role in a variety of signaling networks and HER2 peculiarity, it has been suggested that HER2’s role within the family is to amplify the other proteins’ signals (Arkhipov et al., 2013). Scientists discovered that estrogen can activate HER2 signaling activities through ER’s non-genomic activity outside of the nucleus (Iqbal and Iqbal, 2014). Non-genomic activity is mediated by ERs residing in the membrane and/or cytoplasm due to some estrogen gene expression effects being too rapid to depend on the activation of RNA and protein synthesis (Bjornstrom and Sjoberg, 2005). Estrogen induces non-genomic signaling on ER residing at the membrane and/or cytoplasm, the interaction of this induction and other signaling intermediate molecules activate growth factor tyrosine kinase receptors such as HER2 (Arpino et al. 2008). Because of HER2's inability to bind with other EGF-link ligands, it sorely depends on other members of the EGFR family or estrogen for activation. However, as a result of TNBC’s negative ER status, it is possible for HER2 activation to be affected by the lack of estrogen, therefore fully or partially inhibiting HER2 signaling.
The Relationship Between BRCA1 and Progesterone Receptors
The interaction between Progesterone Receptors and BRCA1 is poorly understood. Studies show a close relationship between PR and ER-alpha signaling, however, this relationship is difficult to study due to PR status as a target gene of ER (Brisken and Scabia, 2020). Other studies suggest that BRCA1 deficiency dysregulates progesterone signaling (Lee et al., 2021), and the over-expression of BRCA1 inhibits the expression of various progesteroneresponsive genes (Katiyar et al., 2006). Although these studies indicate an interplay between PR and BRCA1, as well as PR and ER, the expression mechanisms of progesterone are still a mystery to the scientific community.
Discussion and Conclusion
Studies are needed to elucidate the relationship between BRCA1 and its receptors, ER, PR, and HER2 in Triple Negative Breast Cancer to decipher how BRCA1 affects the expression mechanisms of these receptors, as well as how the receptors affect the expression of BRCA1. This analysis suggests that BRCA1’s complex interplay of pathways plays a significant role in the expression of multiple receptors, including ER, PR, and HER2. Because of the interplay between BRCA1 and the receptors, studies suggest that BRCA1 mutations may inhibit or repress these receptors; this is demonstrated by BRCA1 and ER-alpha mutual regulation during cell proliferation.
The receptors also interact with each other to activate or regulate signaling. This interaction is clearly shown by ER’s non-genomic activity activating HER2 signaling pathways. The lack of HER2 signaling could also be a result of a centromere aneuploidy in chromosome 17 caused by the mutated BRCA1 gene, as this chromosome carries both the BRCA1 and HER2 genes. Aneuploidy in this chromosome is frequently found in breast cancer patients, including HER2-negative patients. However, the interplay between PR and BRCA1, or PR and other receptors is poorly understood and still being studied. Recent research suggests that it could be a mutual regulation with BRCA1 similar to the one between BRCA1 and ER-alpha. Other studies suggest that PR levels are connected with ER levels, but this relationship between PR and ER is difficult to study due to PR’s status as a target gene of ER. ​
Deciphering the relationship between BRCA1 and the receptors can enhance the understanding of TNBC’s aggressive nature, leading to improvement of the treatment options and outcomes of TNBC patients. This research also has the potential to aid in developing new treatment options for TNBC patients and other receptor-negative cancers derived from mutated the BRCA1 gene. Ultimately, in an effort to develop new and better treatment options for TNBC patients and reduce mortality rates within this group, an understanding of the interplay of pathways connected to BRCA1 is essential.
References
Arkhipov, A., Shan, Y., Kim, E. T., Dror, R. O., & Shaw, D. E. (2013). Her2 activation mechanism reflects evolutionary preservation of asymmetric ectodomain dimers in the human EGFR family. ELife, 2. https://doi.org/10.7554/eLife.00708
Arpino, G., Wiechmann, L., Osborne, C. K., & Schiff, R. (2008). Crosstalk between the Estrogen Receptor and the HER Tyrosine Kinase Receptor Family: Molecular Mechanism and Clinical Implications for Endocrine Therapy Resistance. Endocrine Reviews, 29(2), 217-233. https://doi.org/10.1210/er.2006-0045
Bjornstrom, L., & Sjobern, M. (2005). Mechanisms of Estrogen Receptor Signaling: Convergence of Genomic and Nongenomic Actions on Target Genes. Molecular Endocrinology, 19(4), 833-842. https://doi.org/10.1210/me.2004-0486
Brisken, C., & Scabia, V. (2020). 90 YEARS OF PROGESTERONE: Progesterone receptor signaling in the normal breast and its implications for cancer. Journal of molecular endocrinology, 65(1), T81–T94. https://doi.org/10.1530/JME-20-0091 Casaubon JT, Kashyap S, Regan JP. BRCA1 and BRCA2 Mutations. [Updated 2023 Jul 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470239/
Chen, P., & Li, B. (2022). Role of estrogen receptors in health and disease. Frontiers in Endocrinology, 13, 839005. https://doi.org/10.3389/fendo.2022.839005 Chromosome 17: MedlinePlus Genetics. (n.d.). https://medlineplus.gov/genetics/chromosome/17/#:~:text=Changes%20in%20chromo some%2017%20have,occurs%20frequently%20in%20some%20cancers. Davaadelger, B., Choi, MR., Singhal, H. et al. BRCA1 mutation influences progesterone response in human benign mammary organoids. Breast Cancer Res 21, 124 (2019). https://doi.org/10.1186/s13058-019-1214-0
Di Paolo, A., Racca, C., Calsou, P., & Larminat, F. (2014). Loss of BRCA1 impairs centromeric cohesion and triggers chromosomal instability. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 28(12), 5250–5261. https://doi.org/10.1096/fj.14-250266
Fuentes, N., & Silveyra, P. (2019). Estrogen receptor signaling mechanisms. Advances in Protein Chemistry and Structural Biology, 116, 135. https://doi.org/10.1016/bs.apcsb.2019.01.001
Gorodetska, I., Kozeretska, I., & Dubrovska, A. (2019). BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance. Journal of Cancer, 10(9), 2109-2127. https://doi.org/10.7150/jca.30410
Halilovic, A., Verweij, D. I., Simons, A., L. Stevens-Kroef, J. P., Vermeulen, S., Elsink, J., J. Tops, B. B., Otte-Höller, I., A. Boelens, O. B., Schlooz-Vries, M. S., Dijkstra, J. R., Nagtegaal, I. D., Tol, J., Span, P. N., & Bult, P. (2019). HER2, chromosome 17 polysomy and DNA ploidy status in breast cancer; a translational study. Scientific Reports, 9. https://doi.org/10.1038/s41598-019-48212-2
Iqbal, N., & Iqbal, N. (2014). Human Epidermal Growth Factor Receptor 2 (HER2) in Cancers: Overexpression and Therapeutic Implications. Molecular Biology International, 2014. https://doi.org/10.1155/2014/852748
Oukseub Lee, Maarten C. Bosland, Minhua Wang, Ali Shidfar, Omid Hosseini, Xiaoling Xuei, Priyam Patel, Matthew J. Schipma, Irene Helenowski, J. Julie Kim, Susan E. Clare, Seema A. Khan, Selective progesterone receptor blockade prevents BRCA1-associated mouse mammary tumors through modulation of epithelial and stromal genes, Cancer Letters, Volume 520, 2021, Pages 255-266, ISSN 0304-3835, https://doi.org/10.1016/j.canlet.2021.07.034.
Suba, Z. (2015). DNA stabilization by the upregulation of estrogen signaling in BRCA gene mutation carriers. Drug Design, Development and Therapy, 9, 2663-2675. https://doi.org/10.2147/DDDT.S84437
Treeck, O., Schüler-Toprak, S., & Ortmann, O. (2020). Estrogen Actions in TripleNegative Breast Cancer. Cells, 9(11). https://doi.org/10.3390/cells9112358 Wang, C., Bai, F., Scott, A., Li, E., & Pei, H. (2018). Estrogen promotes estrogen receptor negative BRCA1-deficient tumor initiation and progression. Breast Cancer Research : BCR, 20. https://doi.org/10.1186/s13058-018-0996-9
Yin, L., Duan, JJ., Bian, XW. et al. Triple-negative breast cancer molecular subtyping and treatment progress. Breast Cancer Res 22, 61 (2020). https://doi.org/10.1186/s13058- 020-01296-5
Yoshino, Y., Fang, Z., Qi, H., Kobayashi, A., & Chiba, N. (2021). Dysregulation of the centrosome induced by BRCA1 deficiency contributes to tissue-specific carcinogenesis. Cancer Science, 112(5), 1679-1687. https://doi.org/10.1111/cas.14859