Oncogenic role of microRNA‐155 in mycosis fungoides: an in vitro and xenograft mouse model study

Summary Background MicroRNA (miR)‐155 contributes to the proliferation of mycosis fungoides (MF) in vitro and is upregulated in tumours of MF compared with early MF lesions. Objectives To investigate the contribution of miR‐155 to the cancerous phenotype and drug resistance of MF/Sézary 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 controls. Cells were analysed for response to inducers of apoptosis and cell‐cycle arrest, using fluorescence‐activated cell sorting. Transduced MyLa cells were subcutaneously injected into severe combined immunodeficient mice, and tumours were analysed immunohistochemically and for final size. Result MyLa and MJ cells expressed a high level of miR‐155; Hut78 cells expressed a low level. MF cell lines stably expressing miR‐155 inhibitor showed increased G2/M arrest in response to N‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl quinazolin‐4‐amine) (SL111), an inducer of cell‐cycle arrest, followed by increased apoptosis. Additionally, they showed increased apoptosis in response to suberoylanilide hydroxamic acid (SAHA). Tumours formed in mice from injected anti‐miR‐155‐expressing MyLa cells had a significantly lower volume and higher occurrence of 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 tumour growth. These findings have implications for the potential development of novel therapeutic modalities for MF incorporating miR‐155 inhibitors. What's already known about this topic? MicroRNA (miR)‐155 contributes to the proliferation of MyLa cells. miR‐155 is upregulated in tumours of mycosis fungoides (MF) compared with early‐stage MF lesions. What does this study add? miR‐155 contributes to the apoptosis resistance of MyLa and MJ cells in response to apoptotic drugs. miR‐155 interrupts drug‐induced G2/M arrest in MyLa and MJ cells. miR‐155 facilitates tumour growth by decreasing apoptosis of MyLa cells in a xenograft mouse model. What is the translational message? miR‐155 inhibitor or anti‐miR‐155 may serve as a monotherapy to reduce the growth and progression of tumour MF. mi