hnRNP K Overexpression Drives Myeloid Malignancy Via Interaction with RUNX1

Acute myeloid leukemia (AML) is a conglomerate of hematologic malignancies characterized by recurrent genetic and/or chromosomal aberrations. Recent development of targeted agents has bolstered our armamentarium of therapeutic options and improved outcomes for many patients. Acquiring deeper mechanistic understanding of myeloid leukemogenesis will provide a basis for development of even more therapeutic strategies and further improve patient outcomes.

Our clinical data have revealed that overexpression of HNRNPK is a recurrent abnormality that occurs in upwards of 20% of AML cases at both the RNA and protein levels. Using bone marrow samples from a similar proportion of patients, we have recently discovered a supernumerary marker chromosome containing an extra copy of the HNRNPK locus that is not detectable with routine cytogenetic testing. We have further associated high hnRNP K protein levels with decreased overall survival in de novo AML, emphasizing the need to understand the role of hnRNP K in myeloid malignancy.

To directly evaluate the oncogenic capacity of hnRNP K, we have overexpressed hnRNP K in murine fetal liver cells (FLCs). Using CyTOF and colony formation assays, we demonstrated that hnRNP K-overexpressing FLCs have altered differentiation potential and self-renewal capacity compared to empty vector controls in vitro. These findings are recapitulated in vivo, as murine recipients of hnRNP K-overexpressing FLCs develop myeloid lineage disease, often manifesting as fatal megakaryocytic leukemia.

To elucidate a mechanism by which hnRNP K causes myeloid disease, we performed hnRNP K immunoprecipitation followed by mass spectrometry in an AML cell line and identified that hnRNP K preferentially interacts with translational machinery, ribosomal subunits, and proteins involved in RNA processing. In conjunction with data from our hnRNP K overexpression models that indicate overexpression of hnRNP K occurs primarily in the cytoplasm, we then performed hnRNP K-RNA immunoprecipitation followed by sequencing (RIP-Seq). We determined that hnRNP K interacts with the transcript of RUNX1-a master regulator of hematopoiesis and a critical player in a myriad of leukemias-including megakaryocytic leukemias like those observed in our mouse models. Using biochemical assays, we have demonstrated that hnRNP K directly binds to consensus sequences in the RUNX1 transcript, and ultimately alters RUNX1 translation. Indeed, mice exhibiting hnRNP K overexpression have increased protein levels of Runx1 in hematopoietic tissues.

Our data demonstrate that hnRNP K overexpression drives myeloid malignancy. Currently, we are screening compounds that will disrupt the interaction between hnRNP K and RUNX1 in our efforts to further understand myeloid biology and ultimately improve outcomes for patients with these diseases.