Szatmari, I. | Search bioRxiv

bioRxiv2023

KDM4-dependent DNA breaks at active promoters facilitate +1 nucleosome eviction

When the effect of various posttranslational histone tail modifications (PTMs) on nucleosome stability was compared in an in situ assay involving agarose-embedded nuclei, the promoter proximal H3K4me3, H3K27ac and H4K8ac positive nucleosomes exhibited relative sensitivity to intercalators as compared to bulk H3-GFP or nucleosomes carrying any of the following marks: H3K27me1, H3K27me2, H3K27me3, H3K9me1, H3K9me2, H3K9me3, H3K36me3, H3K4me0, H3K4me1, H3K4me2, H3K9ac, and H3K14ac. Nickase or DNase I treatment of the nuclei, or bleomycin treatment of live cells, did not affect the stability of nucleosomes carrying H3K4me3 or H3K27ac, while those of the second group were all destabilized upon treatment with intercalators. These observations support the possibility that the promoter proximal marks specify dynamic nucleosomes accomodating relaxed DNA sequences due to DNA breaks generated in vivo. In line with this interpretation, endogeneous, 3OH nicks were mapped within the nucleosome free region of promoters controlling genes active in human mononuclear cells, a conclusion supported by superresolution colocalization studies. The +1 nucleosomes were stabilized and the incidence of nicks was decreased at the promoters upon KDM4a,b,c KO induction (Pedersen et al, EMBO J, 2016) in mouse embryonic stem cells (mES). While etoposide did not further destabilize +1 nucleosomes in control mES, their stabilized state in the KO state was reversed by the drug. A significant fraction of the DNA breaks comprises TOP2-generated nicks according to the results of molecular combing experiments. The chromatin regions harboring nicks are topologicaly separated from the domains containing superhelical chromatin. These observations lend support for a model where the role of DNA strand discontinuities in transcriptional regulation and in higher-order chromatin organization are integrated.

genetics↗

bioRxiv2022

Transglutaminase 2 associated with PI3K and PTEN in a putative membrane-bound signalosome platform blunts cell death

Atypically expressed transglutaminase 2 (TG2) has been identified as a poor prognostic factor in a variety of cancers. In this study, we evaluated the contribution of TG2 to the prolonged cell survival of differentiated acute promyelocytic leukaemia (APL) cells in response to the standard treatment with combined retinoic acid (ATRA) and arsenic trioxide (ATO). We report that one advantage of ATRA + ATO treatment compared to ATRA alone diminishes the amount of activated and non-activated CD11b/CD18 and CD11c/CD18 cell surface integrin receptors. These changes suppress ATRA-induced TG2 docking on the cytosolic part of CD18 {beta}2-integrin subunits and reduce cell survival. In addition, TG2 overexpresses and hyperactivates the phosphatidylinositol-3-kinase (PI3K), phospho-AKT S473, and phospho-mTOR S2481 signalling axis. mTORC2 acts as a functional switch between cell survival and death by promoting the full activation of AKT. We show that TG2 presumably triggers the formation of a signalosome platform, hyperactivates downstream mTORC2-AKT signalling, which in turn phosphorylates and inhibits the activity of FOXO3, a key pro-apoptotic transcription factor. In contrast, the absence of TG2 restores basic phospho-mTOR S2481, phospho-AKT S473, PI3K, and PTEN expression and activity, thereby sensitising APL cells to ATO-induced cell death. We conclude, that atypically expressed TG2 may serve as a hub, facilitating signal transduction via signalosome formation by the CD18 subunit with both PI3K hyperactivation and PTEN inactivation through the PI3K PTEN cycle in ATRA-treated APL cells.

cancer biology↗