Research Highlight: Identification of Tropomyosin 1 as a Downstream Target of mir-21
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 . 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 .
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.
- Zhu S, Si M-L, Wu H, and Mo Y-Y (2007) MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1). J Biol Chem 282(19):14328–14336.
- Si M-L, Zhu S, Wu H, Lu Z, Wu F, and Mo Y-Y (2007) miR-21-mediated tumor growth. Oncogene 26:2799–2803.