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Prostaglandin E2 (PGE 2 ) and 16,16-dimethyl-PGE 2 (dmPGE 2 ) are important regulators of hematopoietic stem and progenitor cell (HSPC) fate and offer potential to enhance stem cell therapies [C. Cutler et al. Blood 122 , 3074–3081(2013); W. Goessling et al. Cell Stem Cell 8 , 445–458 (2011); W. Goessling et al. Cell 136 , 1136–1147 (2009)]. Here, we report that PGE 2 -induced changes in chromatin at enhancer regions through histone-variant H2A.Z permit acute inflammatory gene induction to promote HSPC fate. We found that dmPGE 2 -inducible enhancers retain MNase-accessible, H2A.Z-variant nucleosomes permissive of CREB transcription factor (TF) binding. CREB binding to enhancer nucleosomes following dmPGE 2 stimulation is concomitant with deposition of histone acetyltransferases p300 and Tip60 on chromatin. Subsequent H2A.Z acetylation improves chromatin accessibility at stimuli-responsive enhancers. Our findings support a model where histone-variant nucleosomes retained within inducible enhancers facilitate TF binding. Histone-variant acetylation by TF-associated nucleosome remodelers creates the accessible nucleosome landscape required for immediate enhancer activation and gene induction. Our work provides a mechanism through which inflammatory mediators, such as dmPGE 2 , lead to acute transcriptional changes and modify HSPC behavior to improve stem cell transplantation.

Prostaglandin E2 (PGE2) and 16,16-dimethyl-PGE2 (dmPGE2) are important regulators of hematopoietic stem and progenitor cell (HSPC) fate and offer potential to enhance stem cell therapies1,2. The mechanism of gene regulation in response to dmPGE2 is poorly understood. Here, we show that dmPGE2 regulates inflammatory gene induction by modulating the chromatin architecture and activity of enhancer elements in human HSPCs. We identified the specific genomic reorganization at stimuli-responsive enhancers that permits rapid transcriptional activation. We found that dmPGE2-inducible enhancers retain MNase-accessible, H2A.Z-variant nucleosomes that are permissive to binding of the transcription factor CREB. CREB binding to enhancer nucleosomes is concomitant with deposition of the histone acetyltransferases p300 and Tip60 on chromatin. Subsequent H2A.Z acetylation improves chromatin accessibility at stimuli-responsive enhancers. Our findings support a model where histone variant nucleosomes retained within inducible enhancers facilitate transcription factor (TF) binding. Acetylation of histone variant nucleosomes by TF-associated nucleosome remodelers creates the accessible nucleosome landscape required for immediate enhancer activation and gene induction. Our work provides a mechanism by which inflammatory mediators such as dmPGE2 lead to acute transcriptional changes and alter HSPC behavior.

Background Immune checkpoint inhibitor (ICI) is an essential part of the treatment of various advanced cancers, but its use can be associated with a number of side effects, including hypercalcemia. The mechanism through which hypercalcemia arises is not well established. One proposed mechanism is through sarcoidosis-like reactions. Here we present an illustrative case. Clinical Case A 75-year-old female with past medical history notable for stage IV endometrial adenocarcinoma treated with surgery plus adjuvant chemotherapy, presently on pembrolizumab for 9 months, hypertension, and diabetes was admitted with generalized fatigue, difficulty ambulating, slow movements, and slow speech. Stroke was ruled out with negative neurologic imaging. Blood work revealed elevated calcium 13.8 mg/dL (8.6-10.4 mg/dL) and ionized calcium 1.64 mmol/L (1.09-1.29 mmol/L). Additional workup showed suppressed PTH 7 pg/mL (11-51 pg/mL), 25-OH vitamin D 19 ng/mL (20-50 ng/mL), elevated 1,25(OH)2 vitamin D of 114 pg/mL (19.9-79.3 pg/mL), elevated angiotensin converting enzyme (ACE) level 90 U/L (12-69 U/L), and normal PTHrP, suggestive of PTH-independent hypercalcemia mediated by 1,25(OH)2D as seen in sarcoidosis. Two months prior to admission and seven months after starting pembrolizumab, surveillance CT found improvement in tumor burden but new intrathoracic lymphadenopathy. Lymph node biopsy via bronchoscopy identified non-caseating granulomas suggestive of a sarcoidosis-like reaction. The patient's moderate hypercalcemia was treated with intravenous fluids, calcitonin, and zoledronic acid 4 mg with normalization of calcium levels. Glucocorticoid therapy was initially deferred to avoid counteracting the effect of pembrolizumab, however prednisone 10 mg daily was started 1 month after discharge when calcium rose again to 11.1 mg/dL. Prednisone was tapered off over 8 weeks as her calcium and 1,25(OH)2D levels normalized. She then restarted pembrolizumb, but after the third month she had recurrence of hypercalcemia (calcium 10.8 mg/dL) with elevated 1,25(OH)2D (89.5 pg/mL). She was again treated with prednisone 10 mg daily which was tapered off over 6 weeks with resolution of hypercalcemia. Her calcium levels remained normal off pembrolizumab. The temporal correlation in our case strongly suggests that ICI administration caused sarcoidosis-like granulomas and hypercalcemia. Conclusion Immune checkpoint inhibitors are known to occasionally cause hypercalcemia, although the mechanisms are not well established. In our case, moderate hypercalcemia was likely caused by ICI-induced sarcoid-like granulomas that responded promptly to glucocorticoids and interruption of ICI-therapy. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Monday, June 13, 2022 1:12 p.m. - 1:17 p.m.