The Oncogenic role of miR-155 in Mycosis Fungoides: an in vitro and xenograft mouse model study

Summary

Background

miR-155 contributes to the proliferation of mycosis fungoides (MF) in vitro and is upregulated in tumours of MF compared to early MF lesions.

Objectives

To investigate the contribution of miR-155 to the cancerous phenotype and drug resistance of MF/Sezary cell lines.

Methods

miR-155 was inhibited in MF cell lines (MyLa and MJ) by transduction of miRZip anti-miR-155 and overexpressed in Hut78 cells by transduction of miRVec-miR-155; empty plasmids served as a control. Cells were analysed for response to inducers of apoptosis and cell cycle arrest using FACS. The transduced MyLa cells were subcutaneously injected into SCID mice, and tumours were analysed immunohistochemically and for final size.

Results

MyLa and MJ cells expressed a high level of miR-155 whereas Hut78 cells expressed a low level. MF cell lines stably expressing miR-155 inhibitor showed increased G2/M arrest in response to SL111, a cell-cycle-arrest inducer, followed by increased apoptosis. Additionally, they showed increased apoptosis in response to SAHA, a histone deacetylase inhibitor. Tumours formed in mice from injected anti-miR-155-expressing MyLa cells had a significantly lower volume and more apoptosis than controls. Stable overexpression of miR-155 in Hut78 cells had no effect.

Conclusions

Oncogenic miR-155 appears to contribute to the cancerous phenotype of MyLa and MJ cells, but not of Hut78 cells, by interrupting activation of the G2/M checkpoint in response to SL111 and decreasing apoptosis in response to SL111 and SAHA, thereby facilitating tumor growth. These findings have implications for the potential development of novel therapeutic modalities for MF incorporating miR-155 inhibitors.

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