The Unfolded Protein Response Is a Major Driver of LCN2 Expression in BCR-ABL- and JAK2V617F-Positive MPN

SRSF2 plays an unexpected role as reader of m5C on mRNA, linking epitranscriptomics to cancer

A common mRNA modification is 5-methylcytosine (m5C), whose role in gene-transcript processing and cancer remains unclear. Here, we identify serine/arginine-rich splicing factor 2 (SRSF2) as a reader of m5C and impaired SRSF2 m5C binding as a potential contributor to leukemogenesis. Structurally, we identify residues involved in m5C recognition and the impact of the prevalent leukemia-associated mutation SRSF2P95H. We show that SRSF2 binding and m5C colocalize within transcripts. Furthermore, knocking down the m5C writer NSUN2 decreases mRNA m5C, reduces SRSF2 binding, and alters RNA splicing. We also show that the SRSF2P95H mutation impairs the ability of the protein to read m5C-marked mRNA, notably reducing its binding to key leukemia-related transcripts in leukemic cells. In leukemia patients, low NSUN2 expression leads to mRNA m5C hypomethylation and, combined with SRSF2P95H, predicts poor outcomes. Altogether, we highlight an unrecognized mechanistic link between epitranscriptomics and a key oncogenesis driver.

Inflammation and bone marrow fibrosis: novel immunotherapeutic targets

PURPOSE OF REVIEW

Myelofibrosis (MF) is primarily driven by constitutive activation of the Janus kinase/signal transducer of activators of transcription (JAK/STAT) pathway. While JAK inhibitors have shown to alleviate disease symptoms, their disease-modifying effects in MF are limited. The only curative treatment remains allogeneic stem cell transplantation, which can be applied to a minority of patients. As a result, there is a need to explore novel targets in MF to facilitate appropriate drug development and therapeutic pathways.

RECENT FINDINGS

Recent research has focused on identifying novel signals that contribute to the abnormal cross-talk between hematopoietic and stromal cells, which promotes MF and disease progression. Inflammation and immune dysregulation have emerged as key drivers of both the initiation and progression of MF. A growing number of actionable targets has been identified, including cytokines, transcription factors, signalling networks and cell surface-associated molecules. These targets exhibit dysfunctions in malignant and nonmalignant hematopoietic cells, but also in nonhematopoietic cells of the bone marrow. The study of these inflammation-related molecules, in preclinical models and MF patient's samples, is providing novel therapeutic targets.

SUMMARY

The identification of immunotherapeutic targets is expanding the therapeutic landscape of MF. This review provides a summary of the most recent advancements in the study of immunotherapeutic targets in MF.

Transcriptomic comparison of bone marrow CD34 + cells and peripheral blood neutrophils from ET patients with JAK2 or CALR mutations

BACKGROUND

Essential thrombocythemia (ET) is one of the most common types of Ph-negative myeloproliferative neoplasms, an infrequent group of blood cancers that arise from a CD34 + hematopoietic stem cell (HSC) in the bone marrow (BM) primarily due to driver mutations in JAK2, CALR or MPL. These aberrations result in an overproduction of mature myeloid cells in peripheral blood (PB). To date, no targeted therapies have been approved for ET patients, so the study of the molecular mechanisms behind the disease and the identification of new therapeutic targets may be of interest. For this reason, in this study, we have compared the transcriptomic profile of undifferentiated CD34 + cells and mature myeloid cells from ET patients (CALR and JAK2-mutated) and healthy donors deposited in publicly available databases. The study of the similarities and differences between these samples might help to better understand the molecular mechanisms behind the disease according to the degree of maturation of the malignant clone and the type of mutation and ultimately help identify new therapeutic targets for these patients.

RESULTS

The results show that most of the altered hallmarks in neutrophils were also found in CD34 + cells. However, only a few genes showed a similar aberrant expression pattern in both types of cells. We have identified a signature of six genes common to patients with CALR and JAK2 mutations (BPI, CRISP3, LTF, MMP8, and PTGS1 upregulated, and PBXIP1 downregulated), a different signature of seven genes for patients with CALR mutations (BMP6, CEACAM8, ITK, LCN2, and PRG2 upregulated, and MAN1A1 and MME downregulated) and a signature of 13 genes for patients with JAK2 mutations (ARG1, CAST, CD177, CLEC5A, DAPP1, EPS15, IL18RAP, OLFM4, OLR1, RIOK3, SELP, and THBS1 upregulated, and IGHM downregulated).

CONCLUSIONS

Our results highlight transcriptomic similarities and differences in ET patients according to the degree of maturation of the malignant clone and the type of mutation. The genes and processes altered in both CD34 + cells and mature neutrophils may reveal altered sustained processes that could be studied as future therapeutic targets for ET patients.

Lipocalin 2 inhibits actin glutathionylation to promote invasion and migration

Invasive and metastatic tumor cells show an increase in migration and invasion, making the processes contributing to these phenotypes potential therapeutic targets. Lipocalin 2 (LCN2; also known as neutrophil gelatinase-associated lipocalin) is a putative therapeutic target in multiple tumor types and promotes invasion and migration, although the mechanisms underlying these phenotypes are unclear. The data in this report demonstrate that LCN2 promotes actin polymerization, invasion, and migration by inhibiting actin glutathionylation. LCN2 inhibits actin glutathionylation by decreasing the levels of reactive oxygen species (ROS) and by reducing intracellular iron levels. Inhibiting LCN2 function leads to increased actin glutathionylation, decreased migration, and decreased invasion. These results suggest that LCN2 is a potential therapeutic target in invasive tumors.

Endoplasmic reticulum stress in airway hyperresponsiveness

Airway hyperresponsiveness(AHR) is a major clinical phenomenon in lung diseases (asthma, COPD and pulmonary fibrosis) and not only a high-risk factor for perioperative airway spasm leading to hypoxaemia, haemodynamic instability and even "silent lung", but also a potential risk for increased mortality from underlying diseases (e.g. asthma, COPD). Airway reactivity is closely linked to airway inflammation, remodelling and increased mucus secretion, and endoplasmic reticulum stress is an important mechanism for the development of these pathologies. This review, therefore, focuses on the effects of endoplasmic reticulum stress on the immune cells involved in airway hyperreactivity (epithelial cells, dendritic cells, eosinophils and neutrophils) in inflammation and mucus & sputum secretion; and on the differentiation and remodelling of airway smooth muscle cells and epithelial cells. The aim is to clarify the mechanisms associated with endoplasmic reticulum stress in airway hyperresponsiveness and to find new ideas and methods for the prevention of airway hyperresponsiveness in the perioperative period.

Resident Self-Tissue of Proinflammatory Cytokines Rather than Their Systemic Levels Correlates with Development of Myelofibrosis in Gata1low Mice

Serum levels of inflammatory cytokines are currently investigated as prognosis markers in myelofibrosis, the most severe Philadelphia-negative myeloproliferative neoplasm. We tested this hypothesis in the Gata1low model of myelofibrosis. Gata1low mice, and age-matched wild-type littermates, were analyzed before and after disease onset. We assessed cytokine serum levels by Luminex-bead-assay and ELISA, frequency and cytokine content of stromal cells by flow cytometry, and immunohistochemistry and bone marrow (BM) localization of GFP-tagged hematopoietic stem cells (HSC) by confocal microscopy. Differences in serum levels of 32 inflammatory-cytokines between prefibrotic and fibrotic Gata1low mice and their wild-type littermates were modest. However, BM from fibrotic Gata1low mice contained higher levels of lipocalin-2, CXCL1, and TGF-β1 than wild-type BM. Although frequencies of endothelial cells, mesenchymal cells, osteoblasts, and megakaryocytes were higher than normal in Gata1low BM, the cells which expressed these cytokines the most were malignant megakaryocytes. This increased bioavailability of proinflammatory cytokines was associated with altered HSC localization: Gata1low HSC were localized in the femur diaphysis in areas surrounded by microvessels, neo-bones, and megakaryocytes, while wild-type HSC were localized in the femur epiphysis around adipocytes. In conclusion, bioavailability of inflammatory cytokines in BM, rather than blood levels, possibly by reshaping the HSC niche, correlates with myelofibrosis in Gata1low mice.

Carfilzomib Enhances the Suppressive Effect of Ruxolitinib in Myelofibrosis

As the first FDA-approved tyrosine kinase inhibitor for treatment of patients with myelofibrosis (MF), ruxolitinib improves clinical symptoms but does not lead to eradication of the disease or significant reduction of the mutated allele burden. The resistance of MF clones against the suppressive action of ruxolitinib may be due to intrinsic or extrinsic mechanisms leading to activity of additional pro-survival genes or signalling pathways that function independently of JAK2/STAT5. To identify alternative therapeutic targets, we applied a pooled-shRNA library targeting ~5000 genes to a JAK2^V617F-positive cell line under a variety of conditions, including absence or presence of ruxolitinib and in the presence of a bone marrow microenvironment-like culture medium. We identified several proteasomal gene family members as essential to HEL cell survival. The importance of these genes was validated in MF cells using the proteasomal inhibitor carfilzomib, which also enhanced lethality in combination with ruxolitinib. We also showed that proteasome gene expression is reduced by ruxolitinib in MF CD34⁺ cells and that additional targeting of proteasomal activity by carfilzomib enhances the inhibitory action of ruxolitinib in vitro. Hence, this study suggests a potential role for proteasome inhibitors in combination with ruxolitinib for management of MF patients.