MicroRNA-16 mediates the regulation of a senescence-apoptosis switch in cutaneous T-cell and other non-Hodgkin lymphomas

Multiple sequential genetic and epigenetic alterations underlie cancer development and progression. Overcoming cellular senescence is an early step in cancer pathogenesis. Here, we demonstrate that a noncoding regulatory RNA, microRNA-16 (miR-16), has the potential to induce cellular senescence. First, we examined the expression of miR-16 in primary cutaneous T-cell lymphoma (CTCL) and other non-Hodgkin T/natural killer (NK)-cell lymphomas and found that miR-16 was downregulated than that in the corresponding normal cells. Notably, miR-16 expression was reduced as the primary CTCL progressed from the early stage to the advanced stage. Next, we transduced CTCL cells with miR-16 to examine whether this miRNA exhibited tumor-suppressive effects in CTCL cells. In CTCL cells expressing wild-type p53, forced expression of miR-16 enhanced p21 expression via downregulation of the polycomb group protein Bmi1, thereby inducing cellular senescence. Alternatively, in CTCL cells lacking functional p53, miR-16 induced compensatory apoptosis. The miR-16 transfection significantly decreased senescent cells and increased apoptotic cells in p21-knockdown CTCL cells expressing wild-type p53, suggesting that the presence or absence of p21 may be the most important condition in the senescence-apoptosis switch in CTCL lymphomagenesis. Furthermore, we found that the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) restored the expression of miR-16 and its essential targets, induced senescence in CTCL cells expressing wild-type p53 and promoted apoptosis in cells with nonfunctional p53. Moreover, we found that other T/NK-cell lymphoma cell lines showed similar tumor-suppressive effects in response to miR-16 and SAHA and that these effects were dependent on p53 status. These results suggested that epigenetic silencing of miR-16 may be a key step during lymphoma development. Elucidation of the essential targets of miR-16 and SAHA provides a basis for the clinical application of SAHA in the treatment of CTCL and other non-Hodgkin T/NK-cell lymphomas.