MicroRNA 9-3p Targets β₁ Integrin To Sensitize Claudin-Low Breast Cancer Cells to MEK Inhibition

Abstract

MEK1/2 inhibitors such as AZD6244 are in clinical trials for the treatment of multiple cancers, including breast cancer. Targeted kinase inhibition can induce compensatory kinome changes, rendering single therapeutic agents ineffective. To identify target proteins to be used in a combinatorial approach to inhibit tumor cell growth, we used a novel strategy that identified microRNAs (miRNAs) that synergized with AZD6244 to inhibit the viability of the claudin-low breast cancer cell line MDA-MB-231. Screening of a miRNA mimic library revealed the ability of miR-9-3p to significantly enhance AZD6244-induced extracellular signalregulated kinase inhibition and growth arrest, while miR-9-3p had little effect on growth alone. Promoter methylation of mir-9 genes correlated with low expression of miR-9-3p in different breast cancer cell lines. Consistent with miR-9-3p having synthetic enhancer tumor suppressor characteristics, miR-9-3p expression in combination with MEK inhibitor caused a sustained loss of c-MYC expression and growth inhibition. The ␤ 1 integrin gene (ITGB1) was identified as a new miR-9-3p target, and the growth inhibition seen with small interfering RNA knockdown or antibody blocking of ITGB1 in combination with MEK inhibitor phenocopied the growth inhibition seen with miR-9-3p plus AZD6244. The miRNA screen led to identification of a druggable protein, ITGB1, whose functional inhibition synergizes with MEK inhibitor.

Implications of Different Cancer Stem Cell Phenotypes in Breast Cancer

“…As a consequence, the development of inhibitors that could potentially target these two integrins in breast cancer is required (Table I). Interesting studies have been published with promising results in targeting these integrins such as through the use of short hairpin RNAs or micro-RNAs (94). Targeting gene signaling pathways associated with these integrins or even specific kinases such as feline sarcoma-related kinase, which controls migration and metastasis of IBC cell lines by regulating CD49f-and CD29-integrin-dependent adhesion, is also an interesting approach (95).…”

Investigation of miR9-1, miR9-2 and miR9-3 Methylation in Hodgkin Lymphoma

“…Recently, enormous progress has been made in the discovery of microRNAs and in the evaluation of the DNA methylation effect on this new class of small noncoding RNAs. The methylation of miR9 genes has been studied in various solid cancers [14,15,16,17,18,19,20] and in some hematological malignancies, particularly leukemia [13,21], but, according to our knowledge, no previous study has reported the methylation status of miR9 loci in HL.…”

“…There are 3 genomic loci that code for the same mature miR9 : miR9-1 (1q22), miR9-2 (5q14.3) and miR9-3 (15q26.1) [13]. miR9 has frequently been silenced by hypermethylation in several types of human cancers, including gastric cancer [14], hepatocellular carcinoma [15], breast cancer [16], bladder cancer [17], small-cell lung cancer [18], oral and oropharyngeal squamous-cell carcinoma [19], renal-cell carcinoma [20] and leukemia [13,21]. …”

Differential microRNA expression profiles in HCT116 colorectal cancer cell lines located in the lung and colon

“…Among these miRNAs, several have been reported to be downregulated in cancer cells or tissues in previous years (25)(26)(27)(28)(29). Hsa-miR-99a-5p was demonstrated to be downregulated >2-fold in squamous cell lung carcinoma tissues, compared with normal tissues (25).…”