Minor introns impact on hematopoietic malignancies

In the intricate orchestration of the central dogma, pre-mRNA splicing plays a crucial role in the post-transcriptional process that transforms DNA into mature mRNA. Widely acknowledged as a pivotal RNA processing step, it significantly influences gene expression and alters the functionality of gene product proteins. Although U2-dependent spliceosomes efficiently manage the removal of over 99% of introns, a distinct subset of essential genes undergo splicing with a different intron type, denoted as minor introns, using U12-dependent spliceosomes. Mutations in spliceosome component genes are now recognized as prevalent genetic abnormalities in cancer patients, especially those with hematologic malignancies. Despite the relative rarity of minor introns, genes containing them are evolutionarily conserved and play crucial roles in functions such as the RAS-MAPK pathway. Disruptions in U12-type minor intron splicing caused by mutations in snRNA or its regulatory components significantly contribute to cancer progression. Notably, recurrent mutations associated with myelodysplastic syndrome (MDS) in the minor spliceosome component ZRSR2 underscore its significance. Examination of ZRSR2-mutated MDS cells has revealed that only a subset of minor spliceosome-dependent genes, such as LZTR1, consistently exhibit missplicing. Recent technological advancements have uncovered insights into minor introns, raising inquiries beyond current understanding. This review comprehensively explores the importance of minor intron regulation, the molecular implications of minor (U12-type) spliceosomal mutations and cis-regulatory regions, and the evolutionary progress of studies on minor, aiming to provide a sophisticated understanding of their intricate role in cancer biology.

SETBP1 is dispensable for normal and malignant hematopoiesis

SETBP1 is a potential epigenetic regulator whose hotspot mutations preventing proteasomal degradation are recurrently detected in myeloid malignancies with poor prognosis. It is believed that the mutant SETBP1 exerts amplified effects of wild-type SETBP1 rather than neomorphic functions. This indicates that dysregulated quantitative control of SETBP1 would result in the transformation of hematopoietic cells. However, little is known about the roles of endogenous SETBP1 in malignant and normal hematopoiesis. Thus, we integrated the analyses of primary AML and healthy samples, cancer cell lines, and a newly generated murine model, Vav1-iCre;Setbp1fl/fl. Despite the expression in long-term hematopoietic stem cells, SETBP1 depletion in normal hematopoiesis minimally alters self-renewal, differentiation, or reconstitution in vivo. Indeed, its loss does not profoundly alter transcription or chromatin accessibilities. Furthermore, although AML with high SETBP1 mRNA is associated with genetic and clinical characteristics for dismal outcomes, SETBP1 is dispensable for the development or maintenance of AML. Contrary to the evidence that SETBP1 mutations are restricted to myeloid malignancies, dependency on SETBP1 mRNA expression is not observed in AML. These unexpected results shed light on the unrecognized idea that a physiologically nonessential gene can act as an oncogene when the machinery of protein degradation is damaged.

[Hematological malignancies driven by aberrant splicing]

The process of RNA splicing plays a pivotal role in gene expression and genetic information modification by converting pre-mRNA into mature mRNA. Dysregulation of this process has been associated with aberrant gene expression and function, leading to hematopoietic malignancies. Through recent clinical and mouse model analyses, insights have been gained into the mechanisms underlying splicing factor mutations that aid in myelodysplastic syndrome and acute myeloid leukemia. These mutations affect genes that modulate diverse cellular processes, including chromatin regulation, transcription factors, proliferation signaling, and inflammation pathway. The relationship between aberrant splicing and cancer remains unclear despite progress in understanding the functional consequences of splicing factor mutations. This review focuses on the mechanisms of disease development because of splicing factor mutations and their potential mechanism-based therapeutic applications.

Detailed short-term follow-up high-resolution CT series of differentiation syndrome

A 57-year-old man with acute promyelocytic leukaemia (APML) received induction therapy including all-trans-retinoic acid (ATRA). At day 15, he developed dyspnoea, haemoptysis and hypoxia. Thorax CT demonstrated diffuse ground-glass opacity and consolidation predominantly in dorsal regions, which may reflect increased vascular permeability. He was diagnosed with differentiation syndrome. After dexamethasone was administered and chemotherapy suspended, his symptoms improved and abnormal lesions mostly disappeared on follow-up CT examinations. We report a short-term high-resolution CT series of differentiation syndrome.

[Immunohistochemical evaluation of BCL-2 expression in acute myeloid leukemia, myeloid sarcoma, and blastic plasmacytoid dendritic cell neoplasm]

Venetoclax, a selective BCL-2 inhibitor, is prescribed clinically for acute myeloid leukemia (AML) treatment. However, it is unclear if known chromosomal or genetic abnormalities associated with AML also influence BCL-2 expression. Few studies have examined BCL-2 expression in AML-related precursor neoplasms such as primary myeloid sarcoma (MS) and blastic plasmacytoid dendritic cell neoplasm (BPDCN). In this study, we examined BCL-2 expression using immunohistochemistry in 7 patients with AML, who also carried genetic and chromosomal abnormalities typical to AML including t (8;21), t (15;17), FLT3-ITD mutation, and complex karyotype, along with 1 patient with primary MS and 3 patients with BPDCN. As a result, expression of BCL-2 was observed in all patients with AML and 1 patient with primary MS. In the patients with BPDCN, BCL-2 was highly expressed in all regions with evidence of tumor cell infiltration, such as skin, bone marrow, and lymph node. These results could be used as evidence in the support of administering venetoclax to adverse-risk patients with AML, MS, or BPDCN.