The PIM kinase family consists of 3 proto-oncogenic proteins: PIM1, PIM2 and PIM3, expressed in numerous malignancies, including DLBCL. PIM kinases regulate crucial processes, such as proliferation, apoptosis, metabolism, or migration, therefore their inhibition is of great interest as a potential therapeutic strategy. Although recent studies have shed new light on the biological role of PIMs in lymphoid cancers, the details and mechanisms of PIM's oncogenic effects and the consequences of their inhibition in DLBCL remain insufficiently understood. Earlier studies have demonstrated a potential epigenetic role of PIM through histone H3S10 phosphorylation, however, described only at a single locus. The broad genomic role of PIM in modulating transcription in lymphoma cells remains unclear.
We confirmed the effect of PIM inhibition on histone modifications using small molecule inhibitors as well as genetic silencing of PIM kinases in DLBCL cell lines. PIM kinase inhibition changed the global amounts of histone modifications (including histone H4 pan-acetylation), accompanied by lower phosphorylation of RNA polymerase II, suggesting an involvement of PIMs in the RNA polymerase II pause release/elongation phase of transcription.
Local histone acetylation changes in the enhancer (H3K27ac) and promoter (H3K9ac) regions in response to treatment with the pan-PIM inhibitor were also identified, coupled with gene expression profiling in DLBCL cell lines. PIM inhibition decreased the expression of genes controlled by super-enhancers (SE), i.e. wide regulatory regions responsible for the high level of expression of the most important genes for the cell, including oncogenes. The integrated results of epigenomic and transcriptomic analyses explain the changes in expression of genes associated with many pathways, including transcription, inflammatory response, apoptosis, epigenetic mechanisms or DNA damage. The induction of the latter was further experimentally confirmed by the examination of DNA breaks using γH2AX, the activating phosphorylation of CHK2 or comet assays following PIM inhibition.
The conducted studies document an epigenetic function of PIM kinases, and suggest that inhibition of PIM activity leads to alterations in the DLBCL epigenetic landscape and associated changes in transcription. They also indicate that PIM inhibitors can be a therapeutic option in DLBCL.
Study supported aby Foundation For Polish Science TEAM Grant # POIR.04.04.00-00-5C84/17 and Polish National Science Centre Grant # 2018/29/B/NZ5/01471.
Disclosures
Pawlak:ORIC Pharmaceuticals: Current Employment, Honoraria. Chapuy:BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Honoraria; Regeneron: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sobi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; KML: Honoraria; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; ADC: Consultancy, Membership on an entity's Board of Directors or advisory committees; Ars tempi: Honoraria; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Honoraria, Research Funding; Sandoz: Honoraria; Ono: Honoraria. Juszczyński:RYVU Therapeutics: Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees.
