Research Highlight: Identification of Tropomyosin 1 as a Downstream Target of mir-21

MicroRNAs (miRNAs) are small, highly conserved, noncoding RNA molecules that regulate gene expression post-transcriptionally. Now that many miRNA sequences are known, researchers are increasingly analyzing and comparing miRNA expression levels between different tissues, developmental stages, or disease states and searching for downstream targets of the miRNAs. Here we summarize the research of Dr. Yin-Yuan Mo’s group (Southern Illinois University School of Medicine, Springfield, IL), who used Anti-miR™ miRNA Inhibitors, the Anti-miR Negative Control, TaqMan MicroRNA Assays, and the 7500 Real-Time PCR System in their research on miRNAs and tumorigenesis [1].

Previously, this group had demonstrated that mir-21 functions as an oncogene that modulates tumorigenesis. mir-21 is overexpressed in breast tumor tissues, and treatment with Anti-miR-21 inhibits both cell growth in vitro and tumor growth in vivo [2]. In their most recent publication, Zhu and colleagues used two-dimensional differentiation in-gel electrophoresis (2-DIGE) of proteins from tumors (with and without Anti-miR-21 treatment) to identify the tumor suppressor tropomyosin 1 (TPM1) as a potential target of mir-21 [1].

Further analysis revealed putative mir-21 binding sites in the 3'-untranslated region (3'-UTR) of two TPM1 variants. When the mir-21 binding sites were subcloned into luciferase reporter vectors, luciferase activity was responsive to changes in mir-21 levels: when overexpressed from a plasmid vector, mir-21 down-regulated luciferase activity, while transfection of Anti-miR-21 up-regulated luciferase activity. Moreover, results from Western blots showed that protein levels of a subcloned TPM1 variant with the 3'-UTR sequence were regulated by mir-21, while real-time RT-PCR analysis showed that RNA levels of the TPM1 variant did not change in response to mir-21. Finally, overexpression of TPM1 in a breast cancer cell line suppressed anchorage-independent growth.

Taken together, these results indicate that TPM1 is a mir-21 target and present a mechanism for how mir-21 modulates tumorigenesis.