Pleiotropic actions of miR-21 highlight the critical role of deregulated stromal microRNAs during colorectal cancer progression

Cell Death Dis. 2013 Jun 20;4(6):e684. doi: 10.1038/cddis.2013.213.

Abstract

The oncogene microRNA-21 (miRNA; miR-21) is overexpressed in most solid organ tumours; however, a recent examination of stage II colorectal cancer (CRC) specimens suggests this may be a stromal phenomenon and not only a feature of cancer cells. In vitro and in vivo studies show that miR-21 has potent pro-metastatic effects in various malignant carcinoma cell lines. The tumour microenvironment has also been identified as a key actor during the metastatic cascade; however to date the significance of deregulated miR-21 expression within the cancer-associated stroma has not been examined. In the present study, a quantitative RT-PCR-based analysis of laser microdissected tissue confirmed that miR-21 expression is associated with a four-fold mean increase in CRC stroma compared with normal tissue. In situ hybridisation using locked nucleic acid probes localised miR-21 expression predominantly to fibroblasts within tumour-associated stroma. To study the molecular and biological impact of deregulated stromal miR-21 in CRC, stable ectopic expression was induced in immortalised fibroblasts. This resulted in upregulated α-smooth muscle actin expression implying miR-21 overexpression is driving the fibroblast-to-myofibroblast transdifferentiation. Conditioned medium from miR-21-overexpressing fibroblasts protected CRC cells from oxaliplatin-induced apoptosis and increased their proliferative capacity. 3D organotypic co-cultures containing fibroblasts and CRC cells revealed that ectopic stromal miR-21 expression was associated with increased epithelial invasiveness. Reversion-inducing cysteine-rich protein with kazal motifs, an inhibitor of matrix-remodelling enzyme MMP2, was significantly downregulated by ectopic miR-21 in established and primary colorectal fibroblasts with a reciprocal rise in MMP2 activity. Inhibition of MMP2 abrogated the invasion-promoting effects of ectopic miR-21. This data, which characterises a novel pro-metastatic mechanism mediated by miR-21 in the CRC stroma, highlights the importance of miRNA deregulation within the tumour microenvironment and identifies a potential application for stromal miRNAs as biomarkers in cancer.

MeSH terms

  • Adenocarcinoma / metabolism*
  • Adenocarcinoma / pathology
  • Antineoplastic Agents / pharmacology
  • Apoptosis
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Survival / drug effects
  • Colorectal Neoplasms / metabolism*
  • Colorectal Neoplasms / pathology
  • Drug Resistance, Neoplasm
  • Fibroblasts / metabolism
  • GPI-Linked Proteins / genetics
  • GPI-Linked Proteins / metabolism
  • Gene Expression
  • Gene Expression Regulation, Neoplastic*
  • Genetic Pleiotropy
  • Humans
  • Matrix Metalloproteinase 2 / metabolism
  • MicroRNAs / genetics*
  • MicroRNAs / metabolism
  • Neoplasm Invasiveness
  • Organoplatinum Compounds / pharmacology
  • Oxaliplatin
  • RNA Interference
  • Stromal Cells / metabolism
  • Tumor Microenvironment

Substances

  • Antineoplastic Agents
  • GPI-Linked Proteins
  • MIRN21 microRNA, human
  • MicroRNAs
  • Organoplatinum Compounds
  • RECK protein, human
  • Oxaliplatin
  • MMP2 protein, human
  • Matrix Metalloproteinase 2