Abstract 1900: MiR-222 accelerates the progression of inflammatory breast cancer by targeting tumor suppressor gene p27kip1 (CDKN1B)

Abstract MicroRNAs (miRNAs) are small non-coding RNAs about 18-22 nucleotides in length, whose main role is to regulate gene expression by altering mRNA stability and translation. MicroRNAs have been shown to play a role in many types of cancer, including breast cancer by targeting tumor suppressor genes such as p53, p27, PTEN, BRCA1, BRCA2 and many others. The goal of this study was to investigate the role of miRNAs in inflammatory breast cancer (IBC). IBC is the most aggressive and metastatic form of breast cancer, that is characterized by very rapid progression, poor prognosis, with a 5 year survival outcome of 30-40%. The mechanism that underlies the rapid progression of IBC is currently under intense investigation, and novel approaches are needed to better understand this disease. To understand the role that microRNAs might play in IBC, we conducted next generation sequencing of the miRNAs from two IBC cell line, SUM149 which is a triple negative IBC (ER-, PR-, HER2-), and SUM190 which is HER2 overexpressing, but ER and PR negative (ER-, PR-, HER2+). We found that 463 miRNAs were differentially expressed in the two cell lines, with 243 miRNAs being overexpressed in SUM149 compared to SUM190, while 220 miRNAs were overexpressed in SUM190. Notably, our qPCR analysis confirmed the raw read counts, showing that miR-155, miR-221, and miR-222 were overexpressed in SUM149 as compared to SUM190 cells by 15, 10, and 3 fold respectively. Furthermore, the inhibition of miR-222 in SUM149 resulted in significant reduction in cell proliferation, tumorsphere formation, and migration in these cells as compared to SUM190 cells. Our flow cytometry data showed that there was cell cycle arrest at the G1 phase in SUM149 cells due to miR-222 inhibition, while SUM190 cells showed little or no change. Additionally, Western blot and immunofluorescence analyses showed that the protein levels of p27, which is one of the targets of miR-222, significantly increased in SUM149 cells, but not in SUM190 cells when miR-222 inhibitor was used in these cells. These results suggest that miR-222 may accelerate the progression of some IBCs by targeting tumor suppressor genes, resulting in rapid cell proliferation, and may be a potential therapeutic target for triple negative inflammatory breast cancers. Citation Format: Joshua Were Ogony, Erin Hayes, Jennifer Knapp, Joan Lewis-Wambi. MiR-222 accelerates the progression of inflammatory breast cancer by targeting tumor suppressor gene p27kip1 (CDKN1B). [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 1900.