Link between the EZH2 noncanonical pathway and microtubule organization center polarization during early T lymphopoiesis

Structure and function of the lysine methyltransferase SETD2 in cancer: From histones to cytoskeleton

SETD2 is known to be the unique histone methyltransferase responsible for the trimethylation of the lysine 36 of histone H3 thus generating H3K36me3. This epigenetic mark is critical for transcriptional activation and elongation, DNA repair, mRNA splicing, and DNA methylation. Recurrent SETD2-inactivating mutations and altered H3K36me3 levels are found in cancer at high frequency and numerous studies indicate that SETD2 acts as a tumor suppressor. Recently, SETD2 was further shown to methylate non-histone proteins particularly the cytoskeletal proteins tubulin and actin with subsequent impacts on cytoskeleton structure, mitosis and cell migration. Herein, we provide a review of the role of SETD2 in different cancers with special emphasis on the structural basis of the functions of this key lysine methyltransferase. Moreover, beyond the role of this enzyme in epigenetics and H3K36me3-dependent processes, we highlight the putative role of "non-epigenetic/H3K36me3" functions of SETD2 in cancer, particularly those involving the cytoskeleton.

Chronic Hypergravity Induces a Modification of Histone H3 Lysine 27 Trimethylation at TCRβ Locus in Murine Thymocytes

Gravity changes are major stressors encountered during spaceflight that affect the immune system. We previously evidenced that hypergravity exposure during gestation affects the TCRβ repertoire of newborn pups. To identify the mechanisms underlying this observation, we studied post-translational histone modifications. We first showed that among the four studied post-translational histone H3 modifications, only lysine 27 trimethylation (H3K27me3) is downregulated in the thymus of mice exposed to 2× g for 21 days. We then asked whether the TCRβ locus chromatin structure is altered by hypergravity exposure. ChIP studies performed on four Vβ segments of the murine double-negative SCIET27 thymic cell line, which corresponds to the last maturation stage before V(D)J recombination, revealed increases in H3K27me3 after 2× g exposure. Finally, we evaluated the implication for the EZH2 methyltransferase in the regulation of the H3K27me3 level at these Vβ segments by treating SCIET27 cells with the GSK126-specific inhibitor. These experiments showed that the downregulation of H3K27me3 contributes to the regulation of the Vβ germline transcript expression that precedes V(D)J recombination. These data show that modifications of H3K27me3 at the TCRβ locus likely contribute to an explanation of why the TCR repertoire is affected by gravity changes and imply, for the first time, EZH2 in the regulation of the TCRβ locus chromatin structure.