Early myeloid cells expressing c-KIT isoforms differ in signal transduction, survival and chemotactic responses to Stem Cell Factor

Single-cell gene and isoform expression analysis reveals signatures of ageing in haematopoietic stem and progenitor cells

Single-cell approaches have revealed that the haematopoietic hierarchy is a continuum of differentiation, from stem cell to committed progenitor, marked by changes in gene expression. However, many of these approaches neglect isoform-level information and thus do not capture the extent of alternative splicing within the system. Here, we present an integrated short- and long-read single-cell RNA-seq analysis of haematopoietic stem and progenitor cells. We demonstrate that over half of genes detected in standard short-read single-cell analyses are expressed as multiple, often functionally distinct, isoforms, including many transcription factors and key cytokine receptors. We observe global and HSC-specific changes in gene expression with ageing but limited impact of ageing on isoform usage. Integrating single-cell and cell-type-specific isoform landscape in haematopoiesis thus provides a new reference for comprehensive molecular profiling of heterogeneous tissues, as well as novel insights into transcriptional complexity, cell-type-specific splicing events and consequences of ageing.

Differential mast cell phenotypes in benign versus cancer tissues and prostate cancer oncologic outcomes

We reported previously that high numbers of mast cells in benign (extra-tumoral) regions of the prostate are associated with worse outcomes after radical prostatectomy including biochemical recurrence and the development of metastases. Herein, with a cohort of 384 men, we performed mast cell subtyping and report that higher minimum number of the tryptase-only (MC_T ) subset of extra-tumoral mast cells is associated with increased risk of biochemical recurrence (comparing highest to lowest tertiles: HR 2.32, 95% CI 1.37-3.93; P-trend = 0.002), metastases (HR 3.62, 95% CI 1.75-7.47; P-trend 0.001), and death from prostate cancer (HR 2.87, 95% CI 1.19-6.95; P-trend = 0.02). Preliminary RNA sequencing and comparison of benign versus cancer tissue mast cells revealed differential expression of additional site-specific genes. We further demonstrate that the genes CXCR4 and TFE3 are more highly expressed in tumor-infiltrating mast cells as well as other tumor-infiltrating immune cells and in tumor cells, respectively, and represent an altered tumor microenvironment. KIT variants were also differentially expressed in benign versus cancer tissue mast cells, with KIT variant 1 (GNNK⁺ ) mast cells identified as more prevalent in extra-tumoral regions of the prostate. Finally, using an established mouse model, we found that mast cells do not infiltrate Hi-Myc tumors, providing a model to specifically examine the role of extra-tumoral mast cells in tumorigenesis. Hi-Myc mice crossed to mast cell knockout (Wsh) mice and aged to 1 year revealed a higher degree of pre-invasive lesions and invasive cancer in wild-type mice versus heterozygous and knockout mice. This suggests a dosage effect where higher numbers of extra-tumoral mast cells resulted in higher cancer invasion. Overall, our studies provide further evidence for a role of extra-tumoral mast cells in driving adverse prostate cancer outcomes. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Two Receptors, Two Isoforms, Two Cancers: Comprehensive Analysis of KIT and TrkA Expression in Neuroblastoma and Acute Myeloid Leukemia

Pediatric cancers represent a wide variety of different tumors, though they have unique features that distinguish them from adult cancers. Receptor tyrosine kinases KIT and TrkA functions in AML and NB, respectively, are well-characterized. Though expression of these receptors is found in both tumors, little is known about KIT function in NB and TrkA in AML. By combining gene enrichment analysis with multidimensional scaling we showed that pediatric AMLs with t(8;21) or inv16 and high KIT expression levels stand out from other AML subtypes as they share prominent transcriptomic features exclusively with KIT-overexpressing NBs. We showed that AML cell lines had a predominant expression of an alternative TrkAIII isoform, which reportedly has oncogenic features, while NB cell lines had dominating TrkAI-II isoforms. NB cells, on the other hand, had an abnormal ratio of KIT isoforms as opposed to AML cells. Both SCF and NGF exerted protective action against doxorubicin and cytarabine for t(8;21) AML and NB cells. We identified several gene sets both unique and common for pediatric AML and NB, and this expression is associated with KIT or TrkA levels. NMU, DUSP4, RET, SUSD5, NOS1, and GABRA5 genes are differentially expressed in NBs with high KIT expression and are associated with poor survival in NB. We identified HOXA10, BAG3, and MARCKS genes that are connected with TrkA expression and are marker genes of poor outcome in AML. We also report that SLC18A2, PLXNC1, and MRPL33 gene expression is associated with TrkA or KIT expression levels in both AML and NB, and these genes have a prognostic value for both cancers. Thus, we have provided a comprehensive characterization of TrkA and KIT expression along with the oncogenic signatures of these genes across two pediatric tumors.

Prognostic Value of Her2/neu Expression in Gastrointestinal Stromal Tumors: Immunohistochemical Study

BACKGROUND

Gastrointestinal stromal tumor (GIST) is a relatively rare type of neoplasms. In Egypt, it represents 2.5% of gastrointestinal tumors and 0.3% of all malignancies. Most of the GISTs develop in the stomach.

AIM

To reveal the significance of Her2/neu immunohistochemical expression in GIST and its correlation with other histopathologic parameters and tumor relapse after regular follow-up.

PATIENTS AND METHODS

This study is a retrospective and prospective cohort. It included 32 patients with GISTs, who were resectable with no distant metastasis. Immunohistochemical staining by Her2/neu was performed after complete surgical resection of the tumors with preservation of the pseudocapsule.

RESULTS

In total, 53.1% of cases were men and 46.9% women. Tumors were classified into low-risk (25%), intermediate-risk (21.9%), and high-risk groups (53.1%). Her2/neu expression was negative in 56.3% of GISTs and positive in 43.7%. Its expression was significantly correlated with risk grade (P = .04), tumor size (P = .001), mitotic count (P = .00), and increased risk of relapse (P = .00). Furthermore, tumor relapse was significantly correlated with the tumor mitotic counts (P = .00). Using kappa agreement test, it showed that 4 mitotic counts/50 high-power fields (HPF) was the cutoff value with which the tumor might be associated more with relapse, with 83% sensitivity, 70% specificity, and P value of .003.

CONCLUSIONS

Her2/neu might be used as an independent prognostic marker for tumor recurrence after complete resection of GIST, and the cutoff value of mitotic count that might predict tumor relapse is 4/50 HPF. However, more clinical studies with greater number of cases with fluorescent in situ hybridization integration are recommended.

Hypoxia and MITF regulate KIT oncogenic properties in melanocytes

KIT mutations are frequent in acral, mucosal and chronic sun-damage (CSD) melanoma, but little is known about the mechanisms driving the transformation of KIT-mutated melanocytes into melanoma cells. We showed that exposition of melanocytes harboring the (L576P)KIT mutation to a hypoxic environment induced their transformation into malignant cells. Transformed (L576P)KIT melanocytes showed downregulation of MITF expression characteristic of melanoma initiating cells (MICs). In agreement, these cells were able to form spheres in neural crest cell medium and low-adherence conditions, also a characteristic of MICs. Downregulation of MITF by RNA interference induced transformation of KIT-mutated melanocytes in normoxia and acquisition of a MIC phenotype by these cells. Hence, low level of MITF cooperates with oncogenic KIT to transform melanocytes. Activation of the cAMP pathway in transformed (L576P)KIT melanocytes stimulated MITF expression, and reduced cellular proliferation and sphere formation. These findings highlight the essential role of MITF in revealing the oncogenic activity of KIT in melanocytes and suggest that the cAMP pathway is a therapeutic target in KIT-mutated melanoma.

KIT GNNK splice variants: expression in systemic mastocytosis and influence on the activating potential of the D816V mutation in mast cells

Stem cell factor-dependent KIT activation is an essential process for mast cell homeostasis. The two major splice variants of KIT differ by the presence or absence of four amino acids (GNNK) at the juxta-membrane region of the extracellular domain. We hypothesized that the expression pattern of these variants differs in systemic mastocytosis and that transcripts containing the KIT D816V mutation segregate preferentially to one GNNK variant. A quantitative real-time PCR assay to assess GNNK(-) and GNNK(+) transcripts from bone marrow mononuclear cells was developed. The GNNK(-)/GNNK(+) copy number ratio showed a trend toward a positive correlation with the percentage of neoplastic mast cell involvement, and KIT D816V containing transcripts displayed a significantly elevated GNNK(-)/GNNK(+) copy number ratio. Relative expression of only the GNNK(-) variant correlated with increasing percentage of neoplastic mast cell involvement. A mast cell transfection system revealed that the GNNK(-) isoform of wild type KIT was associated with increased granule formation, histamine content, and growth. When accompanying the KIT D816V mutation, the GNNK(-) isoform enhanced cytokine-free metabolism and moderately reduced sensitivity to the tyrosine kinase inhibitor, PKC412. These data suggest that neoplastic mast cells favor a GNNK(-) variant predominance, which in turn enhances the activating potential of the KIT D816V mutation and thus could influence therapeutic sensitivity in systemic mastocytosis.

Extracellular assembly and activation principles of oncogenic class III receptor tyrosine kinases

Intracellular signalling cascades initiated by class III receptor tyrosine kinases (RTK-IIIs) and their cytokine ligands contribute to haematopoiesis and mesenchymal tissue development. They are also implicated in a wide range of inflammatory disorders and cancers. Recent snapshots of RTK-III ectodomains in complex with cognate cytokines have revealed timely insights into the structural determinants of RTK-III activation, evolution and pathology. Importantly, candidate 'driver' and 'passenger' mutations that have been identified in RTK-IIIs can now be collectively mapped for the first time to structural scaffolds of the corresponding RTK-III ectodomains. Such insights will generate a renewed interest in dissecting the mechanistic effects of such mutations and their therapeutic relevance.

c-Kit is required for growth and survival of the cells of origin of Brca1-mutation-associated breast cancer

BRCA1 mutation-associated breast cancer originates in oestrogen receptor-alpha-negative (ER(-)) progenitors in the mammary luminal epithelium. These cells also express high levels of the Kit gene and a recent study demonstrated a correlation between Brca1 loss and Kit over-expression in the mammary epithelium. However, the functional significance of c-Kit expression in the mammary gland is unknown. To address this, c-Kit(-) and c-Kit(+) mammary epithelial subsets were isolated by flow cytometry, characterised for expression of lineage-specific cell markers and functionally analysed by in vitro colony forming and in vivo transplantation assays. The results confirm that the majority of luminal ER(-) progenitors are c-Kit(+), but also that most stem cells and the differentiated cell populations are c-Kit(-). A subset of c-Kit(+) cells with high proliferative potential was found in the luminal ER(+) population, however, suggesting the existence of a distinct luminal ER(+) progenitor cell type. Analysis of mouse Brca1 mammary tumours demonstrated that they expressed Kit and its downstream effector Lyn at levels comparable to the most strongly c-Kit(+) luminal ER(-) progenitors. Consistent with c-Kit being a progenitor cell marker, in vitro three-dimensional differentiation of c-Kit(+) cells resulted in a loss of c-Kit expression, whereas c-Kit over-expression prevented normal differentiation in vivo. Furthermore, c-Kit was a functional marker of proliferative potential, as c-Kit inhibition by short hairpin knockdown prevented normal epithelial growth and caused cells to undergo apoptosis. Therefore, c-Kit defines distinct progenitor populations in the mammary epithelium and is critical for mammary progenitor survival and proliferation. Importantly, c-Kit is only the second mammary epithelial stem/progenitor marker to be shown to have a functional role in the mammary epithelium and the first marker to be shown to be required for progenitor cell function. The c-Kit signalling network has potential as a target for therapy and/or prevention in BRCA1-associated breast cancer.

Molecular and functional characterization of kita and kitla of the goldfish (Carassius auratus L.)

Kit ligand and its type III tyrosine kinase receptor Kit promotes the survival, proliferation and differentiation of progenitor cells involved in mammalian myelopoiesis. In this study we report on the molecular and functional characterization of kit receptor A (kita) and kit ligand A (kitla) from the goldfish. Both kita and kitla were ubiquitously expressed in goldfish tissues, with higher mRNA levels observed in the kidney and spleen, the major hematopoietic organs of fish. Furthermore, both kita and kitla expressions decreased in a time-dependent manner in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, and the highest expressions of both the receptor and ligand were observed in sorted progenitor cell populations. Activation of mature macrophage cultures increased both kita and kitla expressions. Kit ligand A induced chemotactic response, proliferation and survival of PKM cells in a dose-dependent manner, but did not induce differentiation of early PKM cells. These results are consistent with the role of kita and kitla during myelopoiesis of higher vertebrates and suggest a conserved mechanism of macrophage development throughout vertebrates.