Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks.

The interaction of the tumor necrosis factor receptor (TNFR) family member CD27 on naive CD8+ T (Tn) cells with homotrimeric CD70 on antigen-presenting cells (APCs) is necessary for T cell memory fate determination. Here, we examined CD27 signaling during Tn cell activation and differentiation. In conjunction with T cell receptor (TCR) stimulation, ligation of CD27 by a synthetic trimeric CD70 ligand triggered CD27 internalization and degradation, suggesting active regulation of this signaling axis. Internalized CD27 recruited the signaling adaptor TRAF2 and the phosphatase SHP-1, thereby modulating TCR and CD28 signals. CD27-mediated modulation of TCR signals promoted transcription factor circuits that induced memory rather than effector associated gene programs, which are induced by CD28 costimulation. CD27-costimulated chimeric antigen receptor (CAR)-engineered T cells exhibited improved tumor control compared with CD28-costimulated CAR-T cells. Thus, CD27 signaling during Tn cell activation promotes memory properties with relevance to T cell immunotherapy.

G1 length dictates heterochromatin landscape.

Stem cells have lower facultative heterochromatin as defined by trimethylation of histone H3 lysine 27 (H3K27me3) compared to differentiated cells, however, the underlying mechanism for this observation has been unknown. Because H3K27me3 levels are diluted two-fold in every round of replication and then restored through the rest of the cycle, we reasoned that the cell cycle length could determine the time available for setting total H3K27me3 levels. Here, we demonstrate that a fast cell cycle sets low levels of H3K27me3 in serum-grown murine embryonic stem cells (mESCs). Extending the G1 phase leads to an increase in global H3K27me3 in mESCs due to the formation of de novo Polycomb domains, and the length of the G1/S block correlates with the extent of gain in H3K27me3, arguing that levels of the modification depend on the time available between successive rounds of replication. Similarly, accelerating the cell cycle in HEK293 cells decreases H3K27me3 levels. Finally, we applied this principle in tumor cells that, due to the dominant negative effect of the sub-stoichiometric H3K27M mutant, have reduced H3K27me3. Here, extending G1 using Palbociclib increased H3K27me3 levels, pointing to an unexpected means to rescue the effect of oncohistones. Our results suggest cell cycle length as a universal mechanism to modulate heterochromatin formation and, thus, cellular identity.

KMT2A oncoproteins induce epigenetic resistance to targeted therapies.

Chromosomal translocations involving the Lysine-Methyl-Tansferase-2A ( KMT2A ) locus generate potent oncogenes that cause highly aggressive acute leukemias 1 . KMT2A and the most frequent translocation partners encode proteins that interact with DNA to regulate developmental gene expression 2 . KMT2A-oncogenic fusion proteins (oncoproteins) contribute to the epigenetic mechanisms that allow KMT2A -rearranged leukemias to evade targeted therapies. By profiling the oncoprotein-target sites of 34 KMT2A -rearranged leukemia samples, we find that the genomic enrichment of oncoprotein binding is highly variable between samples. At high levels of expression, the oncoproteins preferentially activate either the lymphoid or myeloid lineage program depending on the fusion partner. These fusion-partner-dependent binding sites correspond to the frequencies of each mutation in acute lymphoid leukemia versus acute myeloid leukemia. By profiling a sample that underwent a lymphoid-to-myeloid lineage switching event in response to lymphoid-directed treatment, we find the global oncoprotein levels are reduced and the oncoprotein-target gene network changes. At lower levels of expression, the oncoprotein shifts to a non-canonical regulatory program that favors the myeloid lineage, and in a subset of resistant patients, the Menin inhibitor Revumenib induces a similar response. The dynamic shifts in KMT2A oncoproteins we describe likely contribute to epigenetic resistance of KMT2A -rearranged leukemias to targeted therapies.