Direct engagement of the PI3K pathway by mutant KIT dominates oncogenic signaling in gastrointestinal stromal tumor.

Gastrointestinal stromal tumors (GISTs) predominantly harbor activating mutations in the receptor tyrosine kinase KIT. To genetically dissect in vivo the requirement of different signal transduction pathways emanating from KIT for tumorigenesis, the oncogenic mutation was combined with point mutations abrogating specific phosphorylation sites on KIT. Compared with single-mutant mice, double-mutant knock-in mice lacking the SRC family kinase-binding site on KIT (pY567) exhibited attenuated MAPK signaling and tumor growth.

Wnt/β-catenin Signaling Contributes to Tumor Malignancy and Is Targetable in Gastrointestinal Stromal Tumor.

Gastrointestinal stromal tumor (GIST) is the most common type of sarcoma and usually harbors either a or mutation. However, the molecular basis for tumor malignancy is not well defined. Although the Wnt/β-catenin signaling pathway is important in a variety of cancers, its role in GIST is uncertain.

PD-1/PD-L1 Blockade Enhances T-cell Activity and Antitumor Efficacy of Imatinib in Gastrointestinal Stromal Tumors.

Purpose: Tyrosine kinase inhibitors are effective in gastrointestinal stromal tumors (GISTs) but often are of transient benefit as resistance commonly develops. Immunotherapy, particularly blockade of the inhibitory receptor programmed death 1 (PD-1) or the ligand programmed death ligand 1 (PD-L1), has shown effectiveness in a variety of cancers. The functional effects of PD-1/PD-L1 blockade are unknown in GISTs.

A dynamic niche provides Kit ligand in a stage-specific manner to the earliest thymocyte progenitors.

Thymic T cell development is initiated from bone-marrow-derived multi potent thymus-seeding progenitors. During the early stages of thymocyte differentiation, progenitors become T cell restricted. However, the cellular environments supporting these critical initial stages of T cell development within the thymic cortex are not known.

Pharmacological Inhibition of KIT Activates MET Signaling in Gastrointestinal Stromal Tumors.

Gastrointestinal stromal tumors (GIST) are the most common adult sarcomas and the oncogenic driver is usually a KIT or PDGFRA mutation. Although GISTs are often initially sensitive to imatinib or other tyrosine kinase inhibitors, resistance generally develops, necessitating backup strategies for therapy. In this study, we determined that a subset of human GIST specimens that acquired imatinib resistance acquired expression of activated forms of the MET oncogene.

Combined inhibition of MAP kinase and KIT signaling synergistically destabilizes ETV1 and suppresses GIST tumor growth.

Unlabelled: Gastrointestinal stromal tumor (GIST), originating from the interstitial cells of Cajal (ICC), is characterized by frequent activating mutations of the KIT receptor tyrosine kinase. Despite the clinical success of imatinib, which targets KIT, most patients with advanced GIST develop resistance and eventually die of the disease. The ETS family transcription factor ETV1 is a master regulator of the ICC lineage.

Increased KIT inhibition enhances therapeutic efficacy in gastrointestinal stromal tumor.

Purpose: Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and a model of targeted molecular therapy. GIST depends on oncogenic KIT signaling and responds to the tyrosine kinase inhibitor imatinib. However, imatinib is rarely curative.

KIT oncogene inhibition drives intratumoral macrophage M2 polarization.

Tumor-associated macrophages (TAMs) are a major component of the cancer microenvironment. Modulation of TAMs is under intense investigation because they are thought to be nearly always of the M2 subtype, which supports tumor growth. Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and typically results from an activating mutation in the KIT oncogene.

KIT receptor gain-of-function in hematopoiesis enhances stem cell self-renewal and promotes progenitor cell expansion.

The KIT receptor tyrosine kinase has important roles in hematopoiesis. We have recently produced a mouse model for imatinib resistant gastrointestinal stromal tumor (GIST) carrying the Kit(V558Δ) and Kit(T669I) (human KIT(T670I) ) mutations found in imatinib-resistant GIST. The Kit(V558Δ;T669I/+) mice developed microcytic erythrocytosis with an increase in erythroid progenitor numbers, a phenotype previously seen only in mouse models of polycythemia vera with alterations in Epo or Jak2.

SDHA loss of function mutations in a subset of young adult wild-type gastrointestinal stromal tumors.

Background: A subset of KIT/PDGFRA wild-type gastrointestinal stromal tumors (WT GIST) have been associated with alteration of the succinate dehydrogenase (SDH) complex II function. A recent report identified four non-syndromic, KIT/PDGFRA WT GIST harboring compound heterozygous or homozygous mutations in SDHA encoding the main subunit of the SDH complex II.

Methods: Next generation sequencing was applied on five pediatric and one young adult WT GIST, by whole exome capture and SOLiD 3-plus system sequencing.

Imatinib resistance and microcytic erythrocytosis in a KitV558Δ;T669I/+ gatekeeper-mutant mouse model of gastrointestinal stromal tumor.

Most gastrointestinal stromal tumors (GISTs) harbor a gain-of-function mutation in the Kit receptor. GIST patients treated with the tyrosine kinase inhibitor imatinib frequently develop imatinib resistance as a result of second-site Kit mutations. To investigate the consequences of second-site Kit mutations on GIST development and imatinib sensitivity, we engineered a mouse model carrying in the endogenous Kit locus both the Kit(V558Δ) mutation found in a familial case of GIST and the Kit(T669I) (human KIT(T670I)) "gatekeeper" mutation found in imatinib-resistant GIST patients.

The expression of the glucocorticoid receptor in human erythroblasts is uniquely regulated by KIT ligand: implications for stress erythropoiesis.

Studies in mice indicated that activation of the erythroid stress pathway requires the presence of both soluble KIT ligand (KITL) and the glucocorticoid receptor (GR). To clarify the relative role of KITL and GR in stress erythropoiesis in humans, the biological activities of soluble full length- (fl-, 26-190 aa), carboxy-terminus truncated (tr-, 26-162 aa) human (hKITL) and murine (mKITL) KITL in cultures of cord blood (CB) mononuclear cells (MNCs) and CD34(pos) cells that mimic either steady state (growth factors alone) or stress (growth factors plus dexamethasone [DXM]) erythropoeisis were investigated. In steady state cultures, the KITLs investigated were equally potent in sustaining growth of hematopoietic colonies and expansion of megakaryocytes (MK) and erythroid precursors (EBs).

CD133 and CD44 are universally overexpressed in GIST and do not represent cancer stem cell markers.

Although imatinib mesylate has been a major breakthrough in the treatment of advanced gastrointestinal stromal tumors (GIST), complete responses are rare and most patients eventually develop resistance to the drug. Thus, the possibility of an imatinib-insensitive cell subpopulation within GIST tumors, harboring stem cell characteristics, may be responsible for the clinical failures. However, the existence of a cancer stem cell component in GIST has not been yet established.

Imatinib potentiates antitumor T cell responses in gastrointestinal stromal tumor through the inhibition of Ido.

Imatinib mesylate targets mutated KIT oncoproteins in gastrointestinal stromal tumor (GIST) and produces a clinical response in 80% of patients. The mechanism is believed to depend predominantly on the inhibition of KIT-driven signals for tumor-cell survival and proliferation. Using a mouse model of spontaneous GIST, we found that the immune system contributes substantially to the antitumor effects of imatinib.

Visualization of the interstitial cells of cajal (ICC) network in mice.

The interstitial cells of Cajal (ICC) are mesenchymal derived "pacemaker cells" of the gastrointestinal (GI) tract that generate spontaneous slow waves required for peristalsis and mediate neuronal input from the enteric nervous system 1. Different subtypes of ICC form distinct networks in the muscularis of the GI tract (2,3). Loss or injury to these networks is associated with a number of motility disorders(4).

Imatinib upregulates compensatory integrin signaling in a mouse model of gastrointestinal stromal tumor and is more effective when combined with dasatinib.

Activating mutations in the Kit receptor tyrosine kinase are associated with gastrointestinal stromal tumor (GIST). Imatinib inhibits Kit and is front-line therapy for GIST. However, imatinib most often elicits a partial response or stable disease, and most GIST patients who initially respond to imatinib eventually acquire resistance.

Kit ligand cytoplasmic domain is essential for basolateral sorting in vivo and has roles in spermatogenesis and hematopoiesis.

Juxtamembrane signaling via the membrane growth factor KitL is critical for Kit mediated functions. KitL has a conserved cytoplasmic domain and has been shown to possess a monomeric leucine-dependent basolateral targeting signal. To investigate the consequences in vivo of impaired basolateral KitL targeting in polarized epithelial cells, we have mutated this critical leucine to alanine using a knock-in strategy.

Mechanisms of sunitinib resistance in gastrointestinal stromal tumors harboring KITAY502-3ins mutation: an in vitro mutagenesis screen for drug resistance.

Purpose: Although tyrosine kinase inhibitors have improved survival in advanced gastrointestinal stromal tumor (GIST), complete response is rare and most patients eventually fail the first-line treatment with imatinib. Sunitinib malate is the only approved second-line therapy for patients with imatinib-resistant or imatinib-intolerant GIST. The clinical benefit of sunitinib is genotype-dependent in regards to both primary and secondary mutations, with GIST patients harboring the KIT(AY502-3ins) exon 9 mutation being the most sensitive.

Kit signaling via PI3K promotes ovarian follicle maturation but is dispensable for primordial follicle activation.

In mammals, primordial follicles are generated early in life and remain dormant for prolonged intervals. Their growth resumes via a process known as primordial follicle activation. Recent genetic studies have demonstrated that phosphoinositide 3-kinase (PI3K) is the essential signaling pathway controlling this process throughout life, acting via Akt to regulate nucleocytoplasmic shuttling of Foxo3, which functions as a downstream molecular switch.

A KIT juxtamembrane PY567 -directed pathway provides nonredundant signals for erythroid progenitor cell development and stress erythropoiesis.

Objective: KITL/KIT can elicit diverse sets of signals within lymphoid, myeloid, mast, and erythroid lineages, and exert distinct effects on growth, survival, migration, adhesion, and secretory responses. Presently, we have applied a PY-mutant allele knockin approach to specifically assess possible roles for KIT-PY567 and KIT-PY719 sites, and coupled pathways, during erythropoiesis.

Materials And Methods: Mouse models used to investigate this problem include those harboring knocked-in KIT(Y567F/Y567F), KIT(Y569F/Y569F), KIT(Y719F,Y719F), and KIT(Y567F/Y567F:Y569F/Y569F) alleles.

Changes in the structure and function of ICC networks in ICC hyperplasia and gastrointestinal stromal tumors.

Background & Aims: Gastrointestinal stromal tumors (GISTs) express the receptor tyrosine kinase c-kit. Approximately 90% of GISTs have gain-of-function mutations in the Kit gene, which leads to its constitutive activation and drives malignant behavior of GISTs. Interstitial cells of Cajal (ICC) express c-kit; however, it is unknown whether uncontrolled hyperplasia of ICC is responsible for GISTs.

Novel V600E BRAF mutations in imatinib-naive and imatinib-resistant gastrointestinal stromal tumors.

BRAF and NRAS are commonly mutated in cancer and represent the most frequent genetic events in malignant melanoma. More recently, a subset of melanomas was shown to overexpress KIT and harbor KIT mutations. Although most gastrointestinal stromal tumors (GISTs) exhibit activating mutations in either KIT or PDGFRA, about 10% of the cases lack mutations in these genes.

Molecular characterization of pediatric gastrointestinal stromal tumors.

Purpose: Pediatric gastrointestinal stromal tumors (GIST) are rare and occur preferentially in females as multifocal gastric tumors, typically lacking mutations in KIT and PDGFRA. As KIT oncoprotein is consistently overexpressed in pediatric GIST, we sought to investigate the activation of KIT downstream targets and alterations of KIT/PDGFRA gene copy number, mine novel therapeutic targets by gene expression, and test tyrosine kinase receptor activation by proteomic profiling.

Experimental Design: Seventeen pediatric GISTs were investigated for KIT/PDGFRA genotype and biochemical activation of KIT downstream targets.

Tumor mitotic rate, size, and location independently predict recurrence after resection of primary gastrointestinal stromal tumor (GIST).

Background: Gastrointestinal stromal tumor (GIST) is the most frequent sarcoma of the intestinal tract and often shows constitutive activation of either the KIT or PDGFRA receptor tyrosine kinases because of gain-of-function mutation. Although the efficacy of tyrosine kinase inhibitors in metastatic GIST depends on tumor mutation status, there have been conflicting reports on the prognostic importance of KIT mutation in primary GIST.

Methods: A total of 127 patients were studied who presented to our institution from 1983 to 2002 with localized primary GIST and underwent complete gross surgical resection of disease.