ABSTRACT
The blood system serves as a key model for cell differentiation and cancer. It is orchestrated by precise spatiotemporal expression of crucial transcription factors. One of the key master regulators in the hematopoietic systems is PU.1. Reduced levels of PU.1 are characteristic for human acute myeloid leukemia (AML) and are known to induce AML in mouse models. Here, we show that transcriptional downregulation of PU.1 is an active process involving an alternative promoter in intron 3 that is induced by RUNX transcription factors driving noncoding antisense transcription. Core-binding factor (CBF) fusions RUNX1-ETO and CBFß-MYH11 in t(8;21) and inv(16) AML, respectively, activate the PU.1 antisense promoter that results in a shift from sense toward antisense transcription and myeloid differentiation blockade. In patients with CBF-AML, we found that an elevated antisense/sense transcript and promoter accessibility ratio represents a hallmark compared with normal karyotype AML or healthy CD34+ cells. Competitive interaction of an enhancer with the proximal or the antisense promoter forms a binary on/off switch for either myeloid or T-cell development. Leukemic CBF fusions thus use a physiological mechanism used by T cells to decrease sense transcription. Our study is the first example of a sense/antisense promoter competition as a crucial functional switch for gene expression perturbation by oncogenes. Hence, this disease mechanism reveals a previously unknown Achilles heel for future precise therapeutic targeting of oncogene-induced chromatin remodeling.
Subject(s)
Core Binding Factor Alpha 2 Subunit/genetics , Core Binding Factor beta Subunit/genetics , Gene Expression Regulation, Leukemic , Leukemia, Myeloid, Acute/genetics , Proto-Oncogene Proteins/genetics , Trans-Activators/genetics , Antisense Elements (Genetics)/genetics , Cell Line, Tumor , Gene Fusion , Humans , Oncogene Proteins, Fusion/genetics , Promoter Regions, Genetic , RUNX1 Translocation Partner 1 Protein/genetics , Tumor Cells, CulturedABSTRACT
The antiproliferative activity of transforming growth factor-ß (TGF-ß) is essential for maintaining normal tissue homeostasis and is lost in many types of tumors. Gene responses that are central to the TGF-ß cytostatic program include activation of the cyclin-dependent kinase inhibitors, p15(Ink4B) and p21(WAF1/Cip1), and repression of c-myc. These gene responses are tightly regulated by a repertoire of transcription factors that include Smad proteins and Sp1. The DLX4 homeobox patterning gene encodes a transcription factor that is absent from most normal adult tissues, but is expressed in a wide variety of malignancies, including lung, breast, prostate and ovarian cancers. In this study, we demonstrate that DLX4 blocks the antiproliferative effect of TGF-ß. DLX4 inhibited TGF-ß-mediated induction of p15(Ink4B) and p21(WAF1/Cip1) expression. DLX4 bound and prevented Smad4 from forming complexes with Smad2 and Smad3, but not with Sp1. However, DLX4 also bound and inhibited DNA-binding activity of Sp1. In addition, DLX4 induced expression of c-myc independently of TGF-ß/Smad signaling. The ability of DLX4 to counteract key transcriptional control mechanisms of the TGF-ß cytostatic program could explain, in part, the resistance of tumors to the antiproliferative effect of TGF-ß.
