PU.1Controls The Expression Of HOTAIRM1 During Granulocytic Differentiation

Long noncoding RNA HOTAIRM1 has been characterized as an essential regulator in all-trans retinoic acid(ATRA)-induced differentiation of acute promyelocytic leukemia(APL)cells.However,the critical transcription factor regulating HOTAIRM1 expression has not yet been identified.In this study,we identified HOTAIRM1 as a novel target of PU.1,a master transcription factor controlling myeloid differentiation.We found that both HOTAIRM1 variants were remarkably up-regulated during ATRA-induced granulocytic differentiation.Such upregulation could be totally abolished by cycloheximide pretreatment,indicating that the induction of HOTAIRM1 required newly synthesized intermediate protein(s).Chromatin immunoprecipitation assays revealed that PU.1 bound the promoter of HOTAIRM1.Coexpression of PU.1 led to the transactivation of the promoter of HOTAIRM1 in the luciferase reporter assay.Mutation and truncation assays showed that the two PU.1 motifs at the +1067/+1123 bp downstream to the transcriptional start site(TSS)were mainly responsible for the PU.1-dependent transactivation.Furthermore,PU.1 knockdown resulted in significant down-regulation of HOTAIRM1,while ectopic expression of PU.1 significantly increased HOTAIRM1,indicating that the in vivo expression of HOTAIRM1 depended on PU.1.Finally,we demonstrated that the low HOTAIRM1 expression in APL cells was attributed to the reduced PU.1 expression rather than the direct binding and repression by PML-RARα,the oncogenic fusion protein responsible for the initiation and development of APL.Collectively,we demonstrated that PU.1 directly activated the expression of HOTAIRM1 through binding the promoter of HOTAIRM1 during granulocytic differentiation.Our findings enrich the knowledge on the regulation of lncRNAs and the underlying mechanisms of the abnormal expression of lncRNAs involved in APL.