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Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer; however, pathogenesis of TNBC has not yet been fully understood. Here, we identified dysregulated microRNAs (miRNAs) by analyzing miRNA microarray of TNBC patients. MiR-371b-5p expression was reduced, and ectopic expression of miR-371b-5p significantly inhibited TNBC progression in vitro and in vivo. In addition, we found that expression of cold shock domain-containing protein E1 (CSDE1), a direct target gene of miR-371b-5p, was upregulated in TNBC cells, and inhibition of CSDE1 alleviated TNBC cell growth by decreasing RAC1 known as pro-metastatic gene. Mechanistically, CSDE1, phosphorylated C-terminal domain (p-CTD) of RNA polymerase II (RNAPII), and CDK7 form a complex, and downregulation of CSDE1 results in weak interaction between RNAPII p-CTD and CDK7, which leads to a decrease in RNAPII p-CTD expression to reduce RAC1 transcript levels in CSDE1-deficient TNBC cells. Our data revealed the oncogenic function of miR-371b/CSDE1 involved in Rac1 transcription regulation, thus providing a basis for the pathological mechanism of TNBC along with potential biomarkers for TNBC. Citation Format: Yesol Kim, Je Yeong Ko, Soo-Been Lee, Jaehee Jun, Yejin Ahn, Jinui Min, Chaewon Oh, Jong Hoon Park. Dysregulated miR-371b-5p/CSDE1/RAC1 axis is involved in pathogenesis of triple-negative breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4738.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer; however, specific prognostic biomarkers have not yet been developed. In this study, we identified dysregulated microRNAs (miRNAs) in TNBC by profiling miRNA and mRNA expression. In patients with TNBC, miR-371b-5p expression was reduced, and miR-371b-5p overexpression significantly mitigated TNBC cell growth, migration, and invasion. In addition, we found that expression of cold shock domain-containing protein E1 (CSDE1), a direct target gene of miR-371b-5p, was upregulated in TNBC cells, and inhibition of CSDE1 expression alleviated TNBC cell growth by regulating RAC1 transcription. Mechanistically, CSDE1, phosphorylated C-terminal domain (p-CTD) of RNA polymerase II (RNAPII), and CDK7 form a complex, and downregulation of CSDE1 leads to weak interaction between RNAPII p-CTD and CDK7, resulting in a decrease in RNAPII p-CTD expression to reduce RAC1 transcript levels in CSDE1-deficient TNBC cells. Our data demonstrate that miR-371b-5p is a tumor-suppressive miRNA that regulates the CSDE1/Rac1 axis and could be a potential prognostic biomarker for TNBC. Citation Format: Jong Hoon Park, Yesol Kim, Je Yeong Ko, Soo-Been Lee, Minah Park. Reduced miR-371b-5p expression drives tumor progression via CSDE1/RAC1 regulation in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5825.

Autophagy has a dual role in the maintenance of cancer stem cells (CSCs), but the precise relationship between autophagy and cancer stemness requires further investigation. In this study, it was found that luminal and triple-negative breast cancer require distinct therapeutic approaches because of their different expressions of autophagy flux. We identified that autophagy flux was inhibited in triple-negative breast cancer (TNBC) CSCs. Moreover, miRNA-181a (miR-181a) is upregulated both in TNBC CSCs and patients. ATG5 and ATG2B participate in the early formation of autophagosomes and were revealed as targets of miR-181a. Inhibition of miR-181a expression led to attenuation of TNBC cancer stemness and an increase in autophagy flux. Furthermore, treatment with curcumin led to attenuation of cancer stemness in TNBC CSCs; the expression of ATG5 and ATG2B was enhanced and there was an increase of autophagy flux. These results indicated that ATG5 and ATG2B are involved in the suppression of cancer stemness in TNBC. In summary, autophagy inhibits cancer stemness through the miR-181a-regulated mechanism in TNBC. Promoting tumor-suppressive autophagy using curcumin may be a potential method for the treatment of TNBC. Citation Format: Jong Hoon Park, Jee Won Park, Yesol Kim, Jaehee Jun, Yejin Ahn. Autophagy regulates cancer stem cell properties in triple negative breast cancer via miR-181a-mediated regulation of ATG5/ATG2B [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5826.

Human breast cancers include cancer stem cell populations as well as nontumorigenic cancer cells. Breast cancer stem cells have self-renewal capability and are resistant to conventional chemotherapy. miRNAs regulate the expression of many target genes; therefore, dysregulation of miRNAs has been associated with the pathogenesis of human diseases, including cancer. However, a role for miRNA dysregulation in stemness and drug resistance has yet to be identified. Members of the miR34 family are reportedly tumor-suppressor miRNAs and are associated with various human cancers. Our results confirm that miR34a expression was downregulated in MCF7/ADR cells compared with MCF7 cells. We hypothesized that this reduction was due to the p53 (TP53) mutation in MCF7/ADR cells. In this study, we found that primary and mature miR34a were suppressed by treatment with p53 RNAi or the dominant-negative p53 mutant in MCF7 cells. Ectopic miR34a expression reduced cancer stem cell properties and increased sensitivity to doxorubicin treatment by directly targeting NOTCH1. Furthermore, tumors from nude mice treated with miR34a were significantly smaller compared with those of mice treated with control lentivirus. Our research suggests that the ectopic expression of miR34a represents a novel therapeutic approach in chemoresistant breast cancer treatment. Cancer Res; 74(24); 7573–82. ©2014 AACR.

Estrogen receptor-alpha is a clinically important therapeutic target for breast cancer. However, tumors that lose ERα are less responsive to anti-estrogens such as tamoxifen. MicroRNAs are small RNAs that regulate expression of their target gene and dysregulations of miRNA has been identified in many diseases including human cancer. However, only a few miRNAs associated with tamoxifen resistance has been reported. In this study, we found that lymphocyte antigen 6 complex, which is a member of the Ly-6/μPAR superfamily and related to breast cancer progression and metastasis, is inversely correlated with ERα expression. We, for the first time, found miRNAs involved in the regulatory molecular mechanism between ERα and LY6K and related to tamoxifen susceptibility in breast cancer. miR-192-5p, induced by LY6K, downregulates ERα directly and induced tamoxifen resistance in ERα-positive breast cancer cells. In addition, re-expression of ERα in ERα-negative breast cancer cells increased miR-500a-3p expression and directly inhibits LY6K expression. Ectopic expression of miR-500a-3p sensitized ERα-negative cells to tamoxifen by increasing apoptosis. Finally, we observed an inverse correlation between LY6K and ERα in primary breast cancer samples. We found that patients with recurrence showed high expression of miR-192-5p after tamoxifen treatments. In addition, expression of miR-500a-3p was significantly correlated to survival outcome. As miRNAs involved in the regulatory mechanism between LY6K and ERα can affect tamoxifen resistance, downregulating miR-192-5p or re-expressing miR-500a-3p could be a potential therapeutic approach for treating tamoxifen resistant patients. Citation Format: Yesol Kim, Dasom Son, Kyung Hyun Yoo, Jong Hoon Park. miRNAs involved in LY6K and estrogen receptor-α contribute to tamoxifen susceptibility in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 482. doi:10.1158/1538-7445.AM2017-482

The human lymphocyte antigen 6 complex locus K (LY6K) belongs to the lympocyte antigen 6/urokinase-type plasminogen activator receptor (Ly-6/uPAR) superfamily which are associated with development of the immune system and carcinogenesis. LY6K is a cancer biomarker and a therapeutic target that induces invasion and metastasis by activating the Raf-1/MEK/ERK signaling pathway and that stimulates cytotoxic T lymphocytes. However, the molecular mechanisms including genetic and epigenetic that determine human LY6K transcription are complete unknown. To elucidate the genetic mechanisms involved in human LY6K gene regulation and expression, multiple cis elements were predicted using TRANSFAC software, and the LY6K regulatory region was identified using the lucifearse assay in the human LY6K gene promoter. We performed chromatin immunoprecipitation, electrophoretic mobility shift analysis, and supershift assays to investigate the transcription factor activity on the LY6K promoter, and the effect of a single nucleotide polymorphism (SNP) and CpG site methylation on AP-1 transcription factor binding affinity. AP-1 and the CREB transcription factor bound to LY6K promoter within -550/-1, which was essential for LY6K expression but only the AP-1 heterodimer, JunD and Fra-1, modulates LY6K gene transcriptional level. A decrease in LY6K was associated with the SNP242 C allele, a polymorphic G/C-SNP at the 242 nucleotide in the LY6K promoter region (rs2585175), or methylation of the CpG site, which was closely located with the AP-1 site by interfering with binding of the AP-1 transcription factor to the LY6K promoter. In summary, AP-1 activation is important role in promoting LY6K gene expression that regulates cell mobility of breast cancer cells, whereas the SNP242 C allele or methylation of the CpG site may reduce the risk of invasion or metastasis by interfering AP-1 activation. And DNA methylation and histone modification in the 5’-flanking region of the LY6K gene plays an important role in LY6K expression in both breast cancer cells and breast cancer. An understanding of genetic and epigenetic changes in LY6K may contribute to the diagnosis of carcinogenic risk and to an enhanced prediction of outcome in patients with breast cancer. Citation Format: Hyun Kyung Kong, Da Som Son, Jong Hoon Park. The regulatory mechanism of human LY6K related to carcinogenesis and metastasis in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2926.

LY6K is associated with development of the immune response and carcinogenesis. Elevated LY6K by AP-1 activation induces invasion and metastasis by activating the ERK signaling pathway. However, the exact epigenetic mechanism of LY6K gene expression has not been clarified. The CpG island and 5′CGI shore in the region around the transcription start site of the LY6K were predicted using the UCSC genome browser and Methprimer software to elucidate the epigenetic mechanism of LY6K gene regulation and expression. We performed the methylation-specific PCR, bisulfite pyro-sequencing, and bisulfite sequencing to investigate the DNA methylation status of CpG sites from −400 to +500 on the LY6K CpG island and 5′CGI shore. ChIP and ChIP-MSP analysis were performed to confirm the histone modification and DNA methylation status. To validate the inverse correlation between LY6K 5′CGI shore methylation and LY6K expression in vivo, we performed bisulfite pyro-sequencing and tissue microarray using breast carcinoma samples. LY6K expression was inversely correlated with methylation status of CGI and 5′CGI shore in the LY6K of human breast cancer. Moreover, DNA methylation status of LY6K was correlated with histone modification. Treatment of 5-Aza-dC with low LY6K expression caused elevated LY6K expression leading to wound healing. An understanding of epigenetic changes in LY6K may contribute to diagnosing carcinogenic risk and to predict the outcome of patients with breast cancer. Citation Format: Hyun Kyung Kong, Sae Jeong Park, Ye Sol Kim, Jong Hoon Park. Epigenetic modification of LY6K in CGI shore and CGI regulates LY6K gene activation and metastatic function in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4771. doi:10.1158/1538-7445.AM2015-4771

Lymphocyte antigen 6 complex locus K (LY6K) is associated with development of the immune response and carcinogenesis. Elevated LY6K by AP-1 activation induces cell invasion and metastasis through activating the Raf-1/MEK/ERK signaling pathway. However, the exact epigenetic mechanism of LY6K gene expression has yet to be clarified. To elucidate the epigenetic mechanism of LY6K gene regulation and expression, CpG island and 5′CGI shore in the region around transcription start site of the LY6K were predicted using UCSC genome browser and Methprimer software. We performed MSP, bisulfite pyro-sequnecing, and bisulfite sequencing to investigate the DNA methylation status of CpG sites from -400 to +500 on the LY6K CGI and 5′CGI shore. Breast cancer cells with low LY6K expression were highly methylated in the both CGI and 5′CGI shore region, whereas high LY6K expression cell lines had low methylation levels. Moreover, 5-Aza-dC, demethylaing agent, treatment of cells with low LY6K expression caused elevation of LY6K expression and finally leads wound healing. To further validate the inverse correlation between LY6K 5′CGI shore methylation and LY6K expression in vivo seen in breast cancer cell lines, we performed bisulfite pyro-sequencing and tissue microarray using breast carcinoma samples. LY6K expression inversely correlates with methylation status and histone modification of 5′CGI shore in the LY6K promoter in human breast cancers. An understanding of epigenetic changes in LY6K may contribute to the diagnosis of carcinogenic risk and to prediction of outcome in patients with breast cancer. Citation Format: Hyun Kyung Kong, Sae Jeong Park, Ye Sol Kim, Jong Hoon Park. Epigenetic modification of LY6K in CGI shore and CGI regulates LY6K gene activation and metastatic function in breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1365. doi:10.1158/1538-7445.AM2014-1365

Background: Lymphocyte antigen 6 complex locus K(LY-6K), a member of LY-6/uPAR receptor superfamily and cancer-testis antigen, is a novel breast cancer biomarker. Also LY-6K is target antigen for the head and neck squamous cell carcinoma, and lung and esophageal carcinoma. Elevated LY-6K induces cell invasion and metastasis through activating the Raf-1/MEK/ERK signaling pathway. However, the molecular mechanisms that mediate regulation of human LY-6K gene expression are completely unknown. Material and Methods: Within the pGL3-basic reporter vector, the −3050/+182 bp fragment, truncated and mutated fragment upstream of the LY-6K gene was subcloned and measured promoter activity. Subsequently, multiple cis elements were identified using several gene tool software (TFSEARCH, TRANSFAC, PROMO and MATCHTM) in the promoter of human LY-6K gene. We investigated the transcription factor and the effect of single nucleotide polymorphism (SNP) on LY-6K promoter activity and transcription factor binding using chromatin immunoprecipitation (ChIP) assays, electrophoretic mobility shift assays (EMSA), and supershift assays. Results: LY-6K gene was expressed in estrogen receptor (ERα) and progesterone receptor (PR)-negative breast cancer cell lines. A novel AP-1 binding site in the LY-6K promoter regulates LY-6K gene expression. A polymorphic C/G-SNP at the 242 nucleotide position in the promoter region (rs2585175, called SNP242) was validated to be located in a PAX-3 transcription binding motif, which is appear with the presence of the G-allele resulting in a ∼54% decrease in LY-6K promoter activity by interfering binding of AP-1 transcription factor. Discussion: The activity of the AP-1 transcription factor plays an important role in cell mobility of breast cancer cells via the promoting of LY-6K gene expression. LY-6K expression is dependent on not AP-1 transcription factor, but also functional SNP242 G-allele. These results suggested that the polymorphism rs2585175 (SNP242), in close proximity of the LY-6K promoter, lead to LY-6K downregulation, and thus, may reduce the risk of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2203. doi:1538-7445.AM2012-2203