HBO1-MLL interaction promotes AF4/ENL/P-TEFb-mediated leukemogenesis

白血病を引き起こすタンパク質間相互作用の発見. 京都大学プレスリリース. 2021-08-31.Leukemic oncoproteins cause uncontrolled self-renewal of hematopoietic progenitors by aberrant gene activation, eventually causing leukemia. However, the molecular mechanism underlying aberrant gene activation remains elusive. Here, we showed that leukemic MLL fusion proteins associate with the HBO1 histone acetyltransferase (HAT) complex through their trithorax homology domain 2 (THD2) in various human cell lines. MLL proteins associated with the HBO1 complex through multiple contacts mediated mainly by the ING4/5 and PHF16 subunits in a chromatin-bound context where histone H3 lysine 4 tri-methylation marks were present. Of the many MLL fusions, MLL-ELL particularly depended on the THD2-mediated association with the HBO1 complex for leukemic transformation. The C-terminal portion of ELL provided a binding platform for multiple factors including AF4, EAF1, and p53. MLL-ELL activated gene expression in murine hematopoietic progenitors by loading an AF4/ENL/P-TEFb (AEP) complex onto the target promoters wherein the HBO1 complex promoted the association with AEP complex over EAF1 and p53. Moreover, the NUP98-HBO1 fusion protein exerted its oncogenic properties via interaction with MLL but not its intrinsic HAT activity. Thus, the interaction between the HBO1 complex and MLL is an important nexus in leukemic transformation, which may serve as a therapeutic target for drug development

Haploinsufficiency of SAMD9L, an Endosome Fusion Facilitator, Causes Myeloid Malignancies in Mice Mimicking Human Diseases with Monosomy 7

SummaryMonosomy 7 and interstitial deletion of 7q (−7/7q−) are well-recognized nonrandom chromosomal abnormalities frequently found among patients with myelodysplastic syndromes (MDSs) and myeloid leukemias. We previously identified candidate myeloid tumor suppressor genes (SAMD9, SAMD9-like = SAMD9L, and Miki) in the 7q21.3 subband. We established SAMD9L-deficient mice and found that SAMD9L+/− mice as well as SAMD9L−/− mice develop myeloid diseases resembling human diseases associated with −7/7q−. SAMD9L-deficient hematopoietic stem cells showed enhanced colony formation potential and in vivo reconstitution ability. SAMD9L localizes in early endosomes. SAMD9L-deficient cells showed delays in homotypic endosome fusion, resulting in persistence of ligand-bound cytokine receptors. These findings suggest that haploinsufficiency of SAMD9L and/or SAMD9 gene(s) contributes to myeloid transformation

Antidepressant Response and Stress Resilience Are Promoted by CART Peptides in GABAergic Neurons of the Anterior Cingulate Cortex

[Background] A key challenge in the understanding and treatment of depression is identifying cell types and molecular mechanisms that mediate behavioral responses to antidepressant drugs. Because treatment responses in clinical depression are heterogeneous, it is crucial to examine treatment responders and nonresponders in preclinical studies. [Methods] We used the large variance in behavioral responses to long-term treatment with multiple classes of antidepressant drugs in different inbred mouse strains and classified the mice into responders and nonresponders based on their response in the forced swim test. Medial prefrontal cortex tissues were subjected to RNA sequencing to identify molecules that are consistently associated across antidepressant responders. We developed and used virus-mediated gene transfer to induce the gene of interest in specific cell types and performed forced swim, sucrose preference, social interaction, and open field tests to investigate antidepressant-like and anxiety-like behaviors. [Results] Cartpt expression was consistently upregulated in responders to four types of antidepressants but not in nonresponders in different mice strains. Responder mice given a single dose of ketamine, a fast-acting non–monoamine-based antidepressant, exhibited high CART peptide expression. CART peptide overexpression in the GABAergic (gamma-aminobutyric acidergic) neurons of the anterior cingulate cortex led to antidepressant-like behavior and drove chronic stress resiliency independently of mouse genetic background. [Conclusions] These data demonstrate that activation of CART peptide signaling in GABAergic neurons of the anterior cingulate cortex is a common molecular mechanism across antidepressant responders and that this pathway also drives stress resilience

Cytokines direct the regulation of Bim and p27^KIP1 mRNA stability by Heat shock cognate protein 70

Previous gene-targeting studies indicated that Bim, a BIB-only death activator, and p27^KIP1, a cydin-dependent kinase inhibitor, regulate total cell number in the body. Cytokines contribute to this process primarily by negatively regulating the steady-state levels of Bim and p27 mRNAs. Here we present a novel mechanism for cytokine-mediated post-transcriptional regulation of Bim and p27 mRNA levels via the activity of Heat shock cognate protein 70 (Hsc70), which enhances the stability of specific mRNAs by binding to AU-rich elements (AREs) in their 3' -untranslated regions. The RNA-binding potential of Hsc70 is regulated by co-chaperones, including Bag-4 (also SODD), CHIP, Hip and Hsp40. Cytokines that down-regulate Bim and p27 operate via Ras-activated signaling pathways, which in turn control the expression or function of these co-chaperones. Thus, exposure of cells to cytokines ultimately leads to the destabilization of Bim and p27 mRNAs and the promotion of cell division and survival. This unanticipated role for a chaperone/co-chaperone complex in the control of mRNA stability appears to be critical for hematopoiesis and leukemogenesis

MLL fusion proteins link transcriptional coactivators to previously active CpG-rich promoters.

Mixed-lineage leukemia (MLL) maintains the expression of cellular memory genes during development, while leukemic MLL fusion proteins aberrantly maintain expression of hematopoietic stem cell program genes such as HOXA9 to cause leukemia. However, the molecular mechanism of gene activation is unclear. Here we show that only two functional modules are necessary and sufficient for target recognition: those that bind to non-methylated CpGs and di-/tri-methylated histone H3 lysine 36 (H3K36me2/3). An artificial protein composed of the two targeting modules and an interaction domain for AF4-family coactivators can functionally substitute for MLL fusion proteins. Because H3K36me2/3 markers are indicative of active transcription, MLL fusion proteins target previously active CpG-rich genes and activate transcription by recruiting coactivators thereto. Our results indicate that such chromatin context-dependent gene activation is the fundamental mechanism by which MLL fusion proteins maintain the expression of the cellular memory/hematopoietic stem cell program genes