Enid Yi Ni Lam

DNA methyltransferase 1 (DNMT1) is essential for mammalian development and is frequently dysregulated in cancer. While its recruitment to hemimethylated DNA by UHRF1 is well established, its broader chromatin occupancy and regulation remain unclear. We show that DNMT1 is enriched at unmethylated CpG islands of actively transcribed genes largely by its CXXC domain. Upon selective catalytic inhibition, DNMT1 redistributes to partially methylated, inaccessible regions in a UHRF1-dependent and RFTS-dependent manner. Although coding gene expression is largely unchanged, sustained DNMT1 inhibition and subsequent global DNA hypomethylation trigger reactivation of endogenous viral elements, including an uncharacterized class of double-stranded RNA mega-intergenic transcripts (mintRNAs) driving a cell-intrinsic viral mimicry response. We identify RNF4 as a major regulator of DNMT1 catalytic function that, beyond its canonical role in DNA–protein crosslink resolution, controls the levels of SUMOylated DNMT1, establishing SUMOylation as a rheostat that regulates DNMT1 activity to maintain DNA methylation and safeguard against viral mimicry.

DOT1L and Menin are essential cofactors for the oncogenic activity of MLL fusion proteins (MLL-FPs) in leukaemia. However, the mechanisms underpinning the therapeutic effects of their inhibitors remain unclear. Here we identify a critical role for the non-canonical Polycomb repressive complex 1.1 (PRC1.1) in mediating the cellular responses to DOT1L and Menin inhibitors. Menin inhibition induces PRC1.1-dependent deposition of H2AK119ub to silence a subset of MLL-FP targets, whereas DOT1L inhibition results in a genome-wide increase in H2AK119ub. We show that enhanced PRC1.1 activity arises specifically from the progressive loss of DOT1L-mediated H3K79 methylation, independent of MLL-FP displacement or transcriptional repression. This regulatory crosstalk is conserved across cell types and is driven by direct biochemical antagonism between H3K79 methylation and PRC1 activity. Together, our findings establish DOT1L as a component of transcriptional memory co-opted in leukaemia and suggest it serves as the missing link balancing the opposing forces of the MLL–Polycomb axis.

CD8 ⁺ T cells are an important weapon in the therapeutic armamentarium against cancer. While CD8 ⁺ CD103 ⁺ T cells with a tissue-resident memory T (T _RM ) cell phenotype are associated with favorable prognoses, the tumor microenvironment also contains dysfunctional exhausted T (T _EX ) cells that exhibit a variety of T _RM -like features. Here we deconvolute T _RM and T _EX cells across human cancers, ascribing markers and gene signatures that distinguish these populations and enable their functional distinction. Although T _RM cells have superior functionality and are associated with long-term survival post-tumor resection, they are not associated with responsiveness to immune checkpoint blockade. Tumor-associated T _EX and T _RM cells are clonally distinct, with the latter comprising tumor-independent bystanders and tumor-specific cells segregated from cognate antigen. Intratumoral T _RM cells can be forced toward an exhausted fate when chronic antigen stimulation occurs, indicating that the presence or absence of continuous antigen exposure within the microenvironment is the key distinction between tumor-associated T _EX and T _RM populations. These results highlight unique functions for T _RM and T _EX cells in tumor control, underscoring the need for distinct strategies to harness these populations for cancer therapies.

Co-culture assays + human PBMC data

PDL1 expression + STM3006 pharmacokinetic studies