MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1). J Biol Chem

Department of Medical Microbiology, Immunology, and Cell Biology, Southern Illinois University School of Medicine, Springfield, IL 62794, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 06/2007; 282(19):14328-36. DOI: 10.1074/jbc.M611393200
Source: PubMed


MicroRNAs are small noncoding RNA molecules that control expression of target genes. Our previous studies show that mir-21 is overexpressed in tumor tissues compared with the matched normal tissues. Moreover, suppression of mir-21 by antisense oligonucleotides inhibits tumor cell growth both in vitro and in vivo. However, it remains largely unclear as to how mir-21 affects tumor growth, because our understanding of mir-21 targets is limited. In this study, we performed two-dimensional differentiation in-gel electrophoresis of tumors treated
with anti-mir-21 and identified the tumor suppressor tropomyosin 1 (TPM1) as a potential mir-21 target. In agreement with this, there is a putative mir-21 binding site at the 3′-untranslated region (3′-UTR) of TPM1 variants V1 and V5. Thus, we cloned the 3′-UTR of TPM1 into a
luciferase reporter and found that although mir-21 down-regulated the luciferase activity, anti-mir-21 up-regulated it. Moreover, deletion of the mir-21 binding site abolished the effect of mir-21 on the luciferase activity, suggesting that this mir-21 binding site is critical. Western blot with the cloned TPM1-V1 plus the 3′-UTR indicated that TPM1 protein level was also
regulated by mir-21, whereas real-time quantitative reverse transcription-PCR revealed no difference at the mRNA level, suggesting translational
regulation. Finally, overexpression of TPM1 in breast cancer MCF-7 cells suppressed anchorage-independent growth. Thus, down-regulation
of TPM1 by mir-21 may explain, at least in part, why suppression of mir-21 can inhibit tumor growth, further supporting the notion that mir-21 functions as an oncogene.

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    • "TPM1 í µí»¾ and í µí»¿ proteins (also known as í µí»¼-tropomyosins) are known to be incorporated into epithelial cell stress fibers. It has been suggested that their expression may be downmodulated in human breast cancers [14] [15] [16] [17] [18] [19] [20] [21]. However, because some novel tropomyosin 1 gene isoforms have been predicted (GenBank accession numbers: XP 005254697, XP 005254698, and XP 006720730) and identified in rat tissues, we decided to explore this issue further [22]. "
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    ABSTRACT: Nine malignant breast epithelial cell lines and 3 normal breast cell lines were examined for stress fiber formation and expression of TPM1 isoform-specific RNAs and proteins. Stress fiber formation was strong (++++) in the normal cell lines and varied among the malignant cell lines (negative to +++). Although TPM1γ and TPM1δ were the dominant transcripts of TPM1, there was no clear evidence for TPM1δ protein expression. Four novel human TPM1 gene RNA isoforms were discovered (λ, μ, ν, and ξ), which were not identified in adult and fetal human cardiac tissues. TPM1λ was the most frequent isoform expressed in the malignant breast cell lines, and it was absent in normal breast epithelial cell lines. By western blotting, we were unable to distinguish between TPM1γ, λ, and ν protein expression, which were the only TPM1 gene protein isoforms potentially expressed. Some malignant cell lines demonstrated increased or decreased expression of these isoforms relative to the normal breast cell lines. Stress fiber formation did not correlate with TPM1γ RNA expression but significantly and inversely correlated with TPM1δ and TPM1λ expression, respectively. The exact differences in expression of these novel isoforms and their functional properties in breast epithelial cells will require further study.
    Full-text · Article · Jul 2015
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    • "Of great importance, the oncogenic effect of mir-21 could be primarily explained by its transcriptional targets and downstream signal pathways. So far, validated targets of mir-21 included programmed cell death 4 gene (PDCD4), tropomyosin 1 (TPM1), phosphatase and tensin homolog (PTEN), chromosome condensation protein G (NCAPG), reticulon 4 isoform A (RTN4) and other cancer-related genes [12]–[15], [17], [44]–[46]. Altogether, the vital cellular pathways regulating cell proliferation, apoptosis and cell cycle such as Ras [47], p53 [48], PI3K-Akt-mTOR pathway [49], as well as target genes compose an intricate network of mir-21 modulation. "
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    ABSTRACT: Background Growing evidence from recent studies has revealed the association of microRNA-21 (mir-21) with outcomes in multiple cancers, but inconsistent findings have been reported, which rationalized a summary and analysis of available data to investigate the prognostic role of mir-21. Materials and Methods Eligible studies were identified through several search strategies and assessed for quality. Data was extracted from studies in terms of baseline characteristics and key statistics such as hazard ratio (HR), 95% confidence interval (CI) and P value, which were utilized to calculate pooled effect size. Results 25 studies were included in the meta-analysis to evaluate the prognostic role of mir-21 in malignant tumors. Elevated mir-21 level was demonstrated to moderately predict poor overall survival (OS) (HR = 1.903, 95% CI: 1.713–2.113, P = 0.000) and disease-free survival (DFS) (HR = 1.574, 95% CI: 1.139–2.175, P = 0.006) by the fixed and random effect model respectively. Importantly, subgroup analysis disclosed significant association between increased mir-21 level in cancerous tissue and worse survival status. Furthermore, over-expression of mir-21 was an independent prognostic factor for non-small cell lung cancer (NSCLC) and pancreatic cancer patients, with the pooled HR being 2.153 (95% CI: 1.693–2.739, P = 0.000) and 1.976 (95% CI: 1.639–2.384, P = 0.000). Conclusions Over-expression of mir-21, especially in cancerous tissue, was effectively predictive of worse prognosis in various carcinomas. Non-invasive circulating mir-21, however, exhibited modest ability to discriminate outcomes. Major concerns about mir-21 assay standardization and selection of specimen need to be fully addressed before its practical implementation in management of cancer.
    Full-text · Article · Aug 2014 · PLoS ONE
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    • "Another four miRNA, miR-21, miR-143, miR-194, and miR-203, were significantly increased in at least one mammary tumor group compared to normal mammary gland and therefore matched the definition of an oncogenic miRNA. While this disease association is new for miR-143 and miR-194, a similar oncogenic function has been suggested for miR-203 [19] in mammary cancer and for miR-21 in several other tumors including human breast cancer but has to be determined yet [20]. "
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    ABSTRACT: MicroRNA has been suspected to be generally involved in carcinogenesis since their first description. A first study supported this assumption for canine mammary tumors when miRNA expression was compared to normal gland. The present study extends these results by comparing the expression of 16 microRNA (miRNA) and 4 small nucleolar RNA (snoRNA) in tumors of different malignancy, for example, adenomas, nonmetastasizing and metastasizing carcinomas as well as lymph node metastases, with each other and with normal mammary gland. All neoplastic tissues differed in their miR-210 expression levels from normal gland. While metastatic cells differed in their expression of mir-29b, miR-101, mir-125a, miR-143, and miR-145 from primary tumors, the comparison of miRNA expression in primary tumors of different malignancy failed to reveal significant differences except for a significant downregulation of mir-125a in metastasizing carcinomas when compared to adenomas.
    Full-text · Article · Apr 2014
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