Simultaneous Sessions II: Lymphoma biology & translational research
Our understanding of how RNA-binding proteins (RBPs) impact hematologic malignancies is poorly understood. Given that RBPs are ubiquitously expressed, their potential contribution to disease pathologies are often overlooked. However, we have identified that one such RBP (hnRNP K) is aberrantly expressed in many cancers. We and others have previously shown that reduced hnRNP K expression down modulates tumor suppressive programs. However, hnRNP K overexpression is the more commonly observed clinical phenomenon, yet the consequence and clinical significance of this overexpression has not been elucidated.
The aim of this study to evaluate the impact of hnRNP K overexpression in the development, progression, and response to therapy in DLBCL.
Clinical implications of hnRNP K overexpression were examined through RNA profiling and immunohistochemistry on samples from patients with diffuse large B-cell lymphoma (DLBCL) who did not harbor MYC alterations. Transgenic mice that overexpresses hnRNP K specifically in B cells were generated to directly examine the role of hnRNP K overexpression in an in vivo setting. The molecular consequences of hnRNP K overexpression were determined through proteomics, formaldehyde-RNA-immunoprecipitation sequencing, and biochemical assays. Therapeutic response to BET-bromodomain inhibition in the context of hnRNP K overexpression was evaluated in vitro and in vivo. The development of hnRNP K-specific inhibitors were identified through an in vitro fluorescence-based screen that disrupts hnRNP K's interactions with its RNA targets. Validation of small molecule inhibitors are currently being validated through cell-based and in vivo assays.
hnRNP K is overexpressed in DLBCL patients without MYC genomic alterations. This overexpression correlates with dismal overall- (p < 0.001) and performance-free survival (p < 0.001), an inability to achieve complete remission (p = 0.0023), IPI Score >2 (0.044) and tumor size ≥5 cm (p = 0.043). Overexpression of hnRNP K in transgenic mice resulted in the development of lymphomas and reduced survival (p < 0.001). Clinical samples, mouse models, global screening assays, and biochemical studies revealed that hnRNP K's oncogenic potential stems from its ability to post-transcriptionally and translationally regulate the expression of oncogenic transcripts (e.g.; MYC). Consequently, Hnrnpk overexpression renders cells sensitive to BET-bromodomain-inhibition in in vitro and transplantation models, which represents a strategy for mitigating hnRNP K-mediated c-Myc activation in patients. Further studies, using fluorescence-anisotropy assays, identified small molecules that specifically disrupt these hnRNP K•MYC interactions. The efficacy of these compounds are now being characterized in vivo.
These findings indicate that increased hnRNP K levels drive c-Myc expression in the absence of MYC translocations or amplifications and that this interaction may be therapeutically targeted.