STAT3-mediated activation of microRNA cluster 17∼92 promotes proliferation and survival of ALK-positive anaplastic large cell lymphoma

Systemic anaplastic large cell lymphoma is a category of T-cell non-Hodgkin's lymphoma which can be further subdivided into two distinct entities (ALK(+) and ALK(-)) based on the presence or absence of ALK gene rearrangements. Among several pathways triggered by ALK signaling, constitutive activation of STAT3 is strictly required for ALK-mediated transformation and survival. Here we performed genome-wide microRNA profiling and identified 48 microRNA concordantly modulated by the inducible knock-down of ALK and STAT3. To evaluate the functional role of differentially expressed miRNA, we forced their expression in ALK(+) anaplastic large cell lymphoma cells, and monitored their influence after STAT3 depletion. We found that the expression of the microRNA-17 similar to 92 cluster partially rescues STAT3 knock-down by sustaining proliferation and survival of ALK+ cells. Experiments in a xenograft mouse model indicated that forced expression of microRNA-17 similar to 92 interferes with STAT3 knock-down in vivo. High expression levels of the microRNA-17 similar to 92 cluster resulted in down-regulation of BIM and TGF beta RII proteins, suggesting that their targeting might mediate resistance to STAT3 knock-down in anaplastic large cell lymphoma cells. We speculate that the microRNA-17 similar to 92 cluster is involved in lymphomagenesis of STAT3(+) ALCL and that its inhibition might represent an alternative avenue to interfere with ALK signaling in anaplastic large cell lymphomas.