Abstract P3-10-06: High levels of miR-18a is associated with increased proliferation but suppression of EMT phenotype in ER negative breast cancer
Authors: Nair Madhumathy G , M Chandrakala , D Apoorva , VP Snijesh , Prabhu Jyothi S , Rajarajan Savitha , Korlimarla Aruna , Ramesh Rakesh S , BS Srinath , TS Sridhar 
Published: March 2022

Introduction: miRNA-based regulation has been implicated in tumor evolution and progression. miR-18a belonging to the miR-17-92 polycistronic cluster has also been reported to have oncogenic effects across multiple cancer types including breast cancer. We have previously demonstrated the epigenetic regulation of ER by miR-18a and its high levels as a poor prognostic marker in ER-positive breast tumors (Nair et al, Cancer Med. 2016). Here, we have examined the effects of high expression of miR-18a in the ER-negative subtype of breast cancer. Methods: 275 surgically excised specimens of primary breast cancers were analyzed. Samples were segregated into ER-positive and ER-negative tumors based on ER positivity as determined by Immunohistochemistry. Relative abundance of hsa-miR-18a-5p in these samples was assessed using a TaqMan qRT-PCR and used to correlate with a probability distribution of proliferation that was derived by fitting a binomial logistic regression model using 4 genes - FOXM1, UBE2C, BIRC5 & ANLN. miR-18a was inhibited using synthetic inhibitors in ER-negative breast cancer cell lines - MDA-MB-468 AND MDA-MB-231. Migratory ability was assessed using wound-healing assays. The expression of miR-18a was further analyzed in ER-negative breast cancer samples from the TCGA (n= 116) and the METABRIC cohort (n=107). ER-negative tumors with higher than the third quartile and lower than the first quartile expression of miR-18a were segregated into tumors with high and low expression, respectively. Functional enrichment of differentially expressed genes (DEGs) between these groups was performed using the G: profiler to identify the deregulated pathways. Result: Evaluation of the levels of miR-18a in 275 breast tumor samples showed that the microRNA was highly expressed (p&lt;0.0001) in the ER-negative tumors (n=105) when compared to ER-positive samples (n=170). The ER-negative tumors were further stratified based on the 3rd quartile expression of miR-18a into high (n=27) and low miR-18a (n=78) expressing tumors. The high miR-18a expressing tumors were associated with a higher proliferation score (p=0.005). Inhibition of miR-18a levels in ER-negative breast cancer increased migration ability up to 33 % in MDA-MB-468 (p=0.009) and up to 26 % in MDA-MB-231 (p=0.0003). Analysis of ER-negative tumors of TCGA and METABRIC cohort revealed that the high miR-18a expressing tumors expressed low levels of EMT master regulators-ZEB1 and ZEB2 and low levels of Matrix metalloproteinases -MMP2, MMP3, MMP10, MMP11, MMP13, and MMP17 (p&lt;0.01). Functional enrichment of differentially expressed genes (DEGs) demonstrated suppression of pathways related to cell motility and migration, ECM activation, Wnt signaling, and Focal adhesion-PI3K-Akt signaling pathways (p&lt;0.01). Conclusion: In ER-positive tumors, high levels of miR-18a are associated with activated EMT, increased migratory ability, and poor prognosis. On the contrary, in ER-negative breast tumors, high levels of miR-18a is associated with a higher rate of proliferation but lower migratory ability and suppression of signaling pathways necessary for an epithelial to mesenchymal transition.

Citation Format: Madhumathy G Nair, Chandrakala M, Apoorva D, Snijesh VP, Jyothi S Prabhu, Savitha Rajarajan, Aruna Korlimarla, Rakesh S Ramesh, Srinath BS, Sridhar TS. High levels of miR-18a is associated with increased proliferation but suppression of EMT phenotype in ER negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-10-06.