RBM15, an RNA binding protein, determines cell-fate specification of many tissues including blood. We demonstrate that RBM15 is methylated by protein arginine methyltransferase 1 (PRMT1) at residue R578, leading to its degradation via ubiquitylation by an E3 ligase (CNOT4). Overexpression of PRMT1 in acute megakaryocytic leukemia cell lines blocks megakaryocyte terminal differentiation by downregulation of RBM15 protein level. Restoring RBM15 protein level rescues megakaryocyte terminal differentiation blocked by PRMT1 overexpression. At the molecular level, RBM15 binds to pre-messenger RNA intronic regions of genes important for megakaryopoiesis such as GATA1, RUNX1, TAL1 and c-MPL. Furthermore, preferential binding of RBM15 to specific intronic regions recruits the splicing factor SF3B1 to the same sites for alternative splicing. Therefore, PRMT1 regulates alternative RNA splicing via reducing RBM15 protein concentration. Targeting PRMT1 may be a curative therapy to restore megakaryocyte differentiation for acute megakaryocytic leukemia.

Metaphase cells have short spindles for efficient bi-orientation of chromosomes. The cohesin proteins hold sister chromatids together, creating Sister Chromatid Cohesion (SCC) that helps in the maintenance of short spindle lengths in metaphase. The budding yeast protein Chl1p, which has human homologs, is required for DNA damage repair, recombination, transcriptional silencing and aging. This protein is also needed to establish SCC between sister chromatids in S-phase.

Introduction: BRIP1 (BRCA1-interacting protein 1) is one of the major interacting partners of BRCA1, which plays an important role in repair by homologous recombination (HR). This gene is mutated in around 4% of cases of breast cancer; however, its mechanism of action is unclear. In this study, we presented the fundamental role of BRCA1 interactors BRIP1 and RAD50 in the development of differential severity in triple-negative breast cancer (TNBC) among various affected individuals. Methods: We have analyzed the expression of DNA repair-related genes in different BC cells using Real-time PCR and western blotting analysis and assessed changes in stemness property and proliferation through Immunophenotyping. We have performed cell cycle analysis to see the defect in checkpoints and also immunofluorescence assay to confirm the accumulation of gamma-H2AX and BRCA1 foci and subsequent incidence. We have performed a severity analysis using TCGA data sets for comparing the expression in MDA-MB-468 MDA-MB-231 and MCF7 cell line. Results: We showed that in some TNBC cell lines such as MDA-MB-231, the functioning of both BRCA1/TP53 is compromised. Furthermore, the sensing of DNA damage is affected. Due to less damage-sensing capability and low availability of BRCA1 at the damage sites, the repair by HR becomes inefficient, leading to more damage. Accumulation of damage sends a signal for over activation of NHEJ repair pathways. Over expressed NHEJ molecules with compromised HR and checkpoint conditions lead to higher proliferation and error-prone repair, which increases the mutation rate and corresponding tumour severity. The in-silico analysis of the TCGA datasets with gene expression in the deceased population showed a significant correlation of BRCA1 expression with overall survival (OS) in TNBCs (0.0272). The association of BRCA1 with OS became stronger with the addition of BRIP1 expression (0.000876**). Conclusion: The severity phenotypes were more in cells having compromised BRCA1-BRIP1 functioning. Since the OS is directly proportional to the extent of severity, the data analysis hints at the role of BRIP1 in controlling the severity of TNBC.

The budding yeast protein Chl1p is a nuclear protein required for sister-chromatid cohesion, transcriptional silencing, rDNA recombination, ageing and plays an instrumental role in chromatin remodeling. This helicase is known to preserve genome integrity and spindle length in S-phase. Here we show additional roles of Chl1p at G1/S phase of the cell cycle following DNA damage.

Thrombopoietin (Thpo) signaling through the c-Mpl receptor promotes either quiescence or proliferation of hematopoietic stem cells (HSCs) in a concentration-dependent manner; however, in vivo Thpo serum levels are responsive to platelet mass rather than HSC demands, suggesting additional regulation exists. Ott1 (Rbm15), a spliceosomal component originally identified as a fusion partner in t(1;22)-associated acute megakaryocytic leukemia, is also essential for maintaining HSC quiescence under stress. Ott1 controls the alternative splicing of a dominant negative isoform, Mpl-TR, capable of inhibiting HSC engraftment and attenuating Thpo signaling. Ott1, which associates with Hdac3 and the histone methyltransferase, Setd1b, binds to both c-Mpl RNA and chromatin and regulates H4 acetylation and H3K4me3 marks. Histone deacetylase or histone methyltransferase inhibition also increases Mpl-TR levels, suggesting that Ott1 uses an underlying epigenetic mechanism to control alternative splicing of c-Mpl. Manipulation of Ott1-dependent alternative splicing may therefore provide a novel pharmacologic avenue for regulating HSC quiescence and proliferation in response to Thpo.