Histone H3.3 Lys27Met mutant (H3.3K27M)

The Histone H3.3 Lys27Met mutant (H3.3K27M) is a somatic, gain-of-function mutation affecting the H3F3A gene encoding the histone variant H3.3, resulting in a lysine to methionine substitution at residue 27 on the histone tail[1][5][7]. This mutation is a molecular hallmark and oncogenic driver of pediatric diffuse intrinsic pontine glioma (DIPG) and related diffuse midline gliomas, occurring in 60–75% of such cases[1][7]. The K27M mutation disrupts normal chromatin regulation by acting as a dominant negative inhibitor of the Polycomb Repressive Complex 2 (PRC2), which normally mediates tri-methylation of H3K27, crucial for transcriptional repression and maintaining cell identity[5][6]. The mutation induces a global decrease in H3K27 trimethylation (H3K27me3) and causes epigenetic reprogramming, with shifts in gene expression that promote oncogenic pathways central to glioma biology and cell proliferation[3][5]. H3.3K27M is not an enzyme, receptor, or transporter, but an oncohistone mutation that fundamentally alters the epigenetic landscape, making it an indirect but essential therapeutic target in these tumors[1][5][7]. Therapeutic targeting focuses largely on modulating the downstream effects of the mutation on chromatin structure and gene expression (e.g., EZH2/PRC2 inhibitors, immunotherapies, and epigenetic modifiers). Testing for the H3.3K27M mutation by genetic or immunohistochemical methods is a standard biomarker approach for diagnosis and patient stratification[5]. There are no therapies directly inhibiting the H3.3K27M protein in clinical practice; challenges include tumor heterogeneity, the essential function of histone H3.3 in normal cells, and the blood-brain barrier in pediatric brainstem tumors[5].

Other names

H3K27MH3F3A K27M mutantHistone H3.3 K27MOncohistone H3.3K27MLys27Met histone H3.3 mutant

Inhibition of PRC2/EZH2 to modulate methylation impaired by H3.3K27M; Immune therapies to direct immune response against mutant peptide; Epigenetic reprogramming