C-kit receptors in childhood malignant lymphoblastic cells

Interplay between transcription regulators RUNX1 and FUBP1 activates an enhancer of the oncogene c-KIT and amplifies cell proliferation

Runt-related transcription factor 1 (RUNX1) is a well-known master regulator of hematopoietic lineages but its mechanisms of action are still not fully understood. Here, we found that RUNX1 localizes on active chromatin together with Far Upstream Binding Protein 1 (FUBP1) in human B-cell precursor lymphoblasts, and that both factors interact in the same transcriptional regulatory complex. RUNX1 and FUBP1 chromatin localization identified c-KIT as a common target gene. We characterized two regulatory regions, at +700 bp and +30 kb within the first intron of c-KIT, bound by both RUNX1 and FUBP1, and that present active histone marks. Based on these regions, we proposed a novel FUBP1 FUSE-like DNA-binding sequence on the +30 kb enhancer. We demonstrated that FUBP1 and RUNX1 cooperate for the regulation of the expression of the oncogene c-KIT. Notably, upregulation of c-KIT expression by FUBP1 and RUNX1 promotes cell proliferation and renders cells more resistant to the c-KIT inhibitor imatinib mesylate, a common therapeutic drug. These results reveal a new mechanism of action of RUNX1 that implicates FUBP1, as a facilitator, to trigger transcriptional regulation of c-KIT and to regulate cell proliferation. Deregulation of this regulatory mechanism may explain some oncogenic function of RUNX1 and FUBP1.

Evaluation of tyrosine-kinase receptor c-kit mutations, mRNA and protein expression in canine lymphoma: might c-kit represent a therapeutic target?

c-kit plays an important role in proliferation, survival and differentiation of hematopoietic progenitor cells. In human hematopoietic malignancies, c-kit is mostly expressed by progenitor cell neoplasms and seldom by mature cell neoplasms. Aim of this study was to evaluate c-kit expression in canine lymphoma. Twenty-five B-cell lymphomas and 21 T-cell lymphomas were enrolled in the study. c-kit mRNA and protein expression was measured in lymph node fine needle aspirates by quantitative real-time RT-PCR, flow cytometry and immunocytochemistry, while the occurrence of KIT mutations on exons 8-11 and 17 was investigated by direct cDNA sequencing. KIT mRNA was amplifiable but below the limit of quantification in 76% of B-cell lymphomas and 33% of T-cell lymphomas. Remaining samples showed a very low expression of KIT, except for some high grade (HG) T-cell lymphomas where a comparatively higher mRNA amount was observed. Transcriptional data were confirmed at the protein level. No gain-of-function mutations were observed. Among canine lymphomas, T-cell lymphoma typically shows an aggressive biological behavior, partly being attributable to the lack of efficacious treatment options, and the evidence of c-kit expression in HG T-cell lymphomas might represent the rationale for its routinely diagnostic evaluation and the use of tyrosine kinase inhibitors in future clinical trials.

The utility of immunohistochemistry for the identification of hematopoietic and lymphoid cells in normal tissues and interpretation of proliferative and inflammatory lesions of mice and rats

Expression of antigens in cells and tissues can be readily studied immunohistochemically with the use of antibodies. A panel of antibodies to cell-specific markers can be used to diagnose lesions, including tumors, in the hematopoietic and lymphoid systems. This review discusses the use of readily available antibodies and procedures to identify antigens expressed in normal tissues and in proliferative and inflammatory lesions in formalin-fixed, paraffin-embedded (FFPE) murine specimens.

KIT (CD117): a review on expression in normal and neoplastic tissues, and mutations and their clinicopathologic correlation

CD117 (KIT) is a type III receptor tyrosine kinase operating in cell signal transduction in several cell types. Normally KIT is activated (phosphorylated) by binding of its ligand, the stem cell factor. This leads to a phosphorylation cascade ultimately activating various transcription factors in different cell types. Such activation regulates apoptosis, cell differentiation, proliferation, chemotaxis, and cell adhesion. KIT-dependent cell types include mast cells, some hematopoietic stem cells, germ cells, melanocytes, and Cajal cells of the gastrointestinal tract, and neoplasms of these cells are examples of KIT-positive tumors. Other KIT-positive normal cells include epithelial cells in skin adnexa, breast, and subsets of cerebellar neurons. KIT positivity has been variably reported in sarcomas such as angiosarcoma, Ewing sarcoma, synovial sarcoma, leiomyosarcoma, and MFH; results of the last three are controversial. The variations in published data may result from incomplete specificity of some polyclonal antibodies, possibly contributed by too high dilutions. Also, KIT is expressed in pulmonary and other small cell carcinomas, adenoid cystic carcinoma, renal chromophobe carcinoma, thymic, and some ovarian and few breast carcinomas. A good KIT antibody reacts with known KIT positive cells, and smooth muscle cells and fibroblasts are negative. KIT deficiency due to hereditary nonsense/missense mutations leads to disruption of KIT-dependent functions such as erythropoiesis, skin pigmentation, fertility, and gastrointestinal motility. Conversely, pathologic activation of KIT through gain-of-function mutations leads to neoplasia of KIT-dependent and KIT-positive cell types at least in three different systems: mast cells/myeloid cells--mastocytosis/acute myeloid leukemia, germ cells--seminoma, and Cajal cells--gastrointestinal stromal tumors (GISTs). KIT tyrosine kinase inhibitors such as imatinib mesylate are the generally accepted treatment of metastatic GISTs, and their availability has prompted an active search for other treatment targets among KIT-positive tumors such as myeloid leukemias and small cell carcinoma of the lung, with variable and often nonconvincing results.

CD117 expression in diffuse large B-cell lymphomas: fact or fiction?

CD117 (KIT) is expressed in a variety of hematopoietic neoplasms but there are a paucity of data regarding its expression in diffuse large B-cell lymphomas (DLBCL). The purpose of the present paper was to describe the authors' experience of two CD117+ DLBCL (one of follicle center-cell origin and one nasal Epstein-Barr virus (EBV)- plasmablastic lymphoma associated with lytic bone lesions), as determined by tissue immunohistochemistry and flow cytometry. The CD117 expression in DLBCL was further evaluated using tissue microarrays and seven additional plasmablastic lymphomas, using two commercially available anti-CD117 antibodies (Ab-1, Oncogene and A4502, DakoCytomation). Membranous +/- cytoplasmic staining was seen with Ab-1 in 24/65 (37%) DLBCL, including 21/56 microarray DLBCL, two index cases, and 1/7 additional plasmablastic lymphomas, with persistent staining in 13% of microarray DLBCL despite preincubation with KIT peptide. However, A4502 had only membranous staining of the index cases and one additional EBV- plasmablastic lymphoma with medullary disease. The present study suggests that (i) CD117 expression can be detected sporadically in DLBCL of follicle center-cell origin and a subset of plasmablastic lymphomas; (ii) staining for CD117 might help in identifying EBV- plasmablastic lymphomas associated with bone marrow involvement; and (iii) CD117 antibodies should be carefully validated prior to use, because non-specific staining, as observed with Ab-1, could lead to false-positive results.

c-Kit triggers dual phosphorylations, which couple activation and degradation of the essential melanocyte factor Mi

Microphthalmia (Mi) is a bHLHZip transcription factor that is essential for melanocyte development and postnatal function. It is thought to regulate both differentiated features of melanocytes such as pigmentation as well as proliferation/survival, based on phenotypes of mutant mouse alleles. Mi activity is controlled by at least two signaling pathways. Melanocyte-stimulating hormone (MSH) promotes transcription of the Mi gene through cAMP elevation, resulting in sustained Mi up-regulation over many hours. c-Kit signaling up-regulates Mi function through MAP kinase phosphorylation of Mi, thereby recruiting the p300 transcriptional coactivator. The current study reveals that c-Kit signaling triggers two phosphorylation events on Mi, which up-regulate transactivation potential yet simultaneously target Mi for ubiquitin-dependent proteolysis. The specific activation/degradation signals derive from MAPK/ERK targeting of serine 73, whereas serine 409 serves as a substrate for p90 Rsk-1. An unphosphorylatable double mutant at these two residues is at once profoundly stable and transcriptionally inert. These c-Kit-induced phosphorylations couple transactivation to proteasome-mediated degradation. c-Kit signaling thus triggers short-lived Mi activation and net Mi degradation, in contrast to the profoundly increased Mi expression after MSH signaling, potentially explaining the functional diversity of this transcription factor in regulating proliferation, survival, and differentiation in melanocytes.

The c-kit receptor and its ligand stem cell factor in childhood malignant lymphoid precursors

The c-kit receptor (CD117) and its ligand stem cell factor (SCF) play an important role in the development, differentiation, and survival of normal and malignant hematopoietic cells. The aim of this work is to review the cellular distribution of this receptor and the effect of SCF on the hematopoietic system, particularly among lymphoid lineage, either in normal or malignant cell progenitors. We examined reports and results in the field and articles or abstracts published in journals covered by MEDLINE. Additionally, we evaluated CD117 expression on fresh blast cells of 376 newly diagnosed cases of childhood acute lymphoblastic leukemia (ALL) that were referred to centers affiliated with the Italian Association for Pediatric Hematology and Oncology (AIEOP). In view of our data, approximately 11% of ALL are CD117 positive. In particular, this receptor can be expressed in 10% and 11.5% of T-lineage and B-lineage ALL, respectively. Its expression is associated with an intermediate/mature phenotype in T-lineage ALL, whereas in B-lineage ALL, the majority of the positive cases are classified as early B ALL. The effect of SCF on malignant hematopoiesis and its potential clinical uses are reviewed.

Practical applications of immunohistochemistry in hematolymphoid neoplasms

Immunohistochemistry plays a key role in the diagnosis and classification of hematolymphoid neoplasms. New cell and lineage markers are constantly being discovered and added to the existing long list of antibodies. In this review article we provide general information and new applications of the commonly used hematolymphoid markers. We also discuss the features and applications of some newly discovered markers, such as ALK, fascin, granzyme/perforin, and tryptase. There is no universal "panel" for the diagnosis of hematolymphoid neoplasms. However, in this review article, we provide suggested panels for a given hematolymphoid neoplasm that is based on our experience and that reported in the literature.