Interleukin (IL)-

IL-17 and its receptor are founding members of a novel family of inflammatory cytokines. IL-17 plays a pathogenic role in rheumatoid arthritis (RA)–associated bone destruction. However, IL-17 is also an important regulator of host defense through granulopoiesis and neutrophil trafficking. Therefore, the role of IL-17 in pathogen-initiated bone loss was not obvious. The most common form of infection-induced bone destruction occurs in periodontal disease (PD). In addition to causing significant morbidity, PD is a risk factor for atherosclerotic heart disease and chronic obstructive pulmonary disease (COPD). Similar to RA, bone destruction in PD is caused by the immune response. However, neutrophils provide critical antimicrobial defense against periodontal organisms. Since IL-17 is bone destructive in RA but a key regulator of neutrophils, we examined its role in inflammatory bone loss induced by the oral pathogen Porphyromonas gingivalis in IL-17RA–deficient mice. These mice showed enhanced periodontal bone destruction, suggesting a bone-protective role for IL-17, reminiscent of a neutrophil deficiency. Although IL-17RA–deficient neutrophils functioned normally ex vivo, IL-17RA knock-out (IL-17RAKO) mice exhibited reduced serum chemokine levels and concomitantly reduced neutrophil migration to bone. Consistently, CXCR2KO mice were highly susceptible to alveolar bone loss; interestingly, these mice also suggested a role for chemokines in maintaining normal bone homeostasis. These results indicate a nonredundant role for IL-17 in mediating host defense via neutrophil mobilization.

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. The transcriptional profile of 13 nodules from 8 pediatric patients was compared with 8 adult wild-type (WT) GISTs, including 3 young adults. The drug sensitivity of second-generation kinase inhibitors was tested in murine Ba/F3 cells expressing human WT KIT, as well as in short-term culture of explants of WT GIST cells. Results: A KIT/PDGFRA WT genotype was identified in all 12 female patients, whereas two of five males had either a KIT exon 11 or PDGFRA exon 18 mutation. KIT downstream targets were consistently activated. Pediatric GISTs showed a distinct transcriptional signature, with overexpression of BAALC, PLAG1, IGF1R, FGF4, and NELL1. In vitro studies showed that nilotinib, sunitinib, dasatinib, and sorafenib are more effective than imatinib against WT KIT. Conclusions: Rare cases of pediatric GIST may occur in male patients and harbor activating KIT/PDGFRA mutations. Pediatric GISTs show distinct transcriptional signature, suggesting a different biology than WT GIST in adults. In vitro drug screening showed that second-generation kinase inhibitors may provide greater clinical benefit in pediatric GIST.Gastrointestinal stromal tumors (GIST), the most common mesenchymal tumors of the gastrointestinal tract, typically occur in adults over the age of 40 years. GISTs in the pediatric age group are rare and account for 1% to 2% of all GIST cases (1, 2). Pediatric GISTs are preferentially located in the stomach as multiple nodules and histologically have either an epithelioid or a mixed spindle and epithelioid morphology (1, 2). Of interest is that unlike in adults, the majority of GISTs in pediatric patients follow an indolent course, in spite of the high rate of metastasis to the peritoneal cavity and liver. Furthermore, metastasis to locoregional lymph nodes is common in pediatric GIST patients and rare in adults (2). Also, in contrast with adult GISTs, tumors in the pediatric age group often lack activating mutations in KIT or PDGFRA. In spite of the wild-type (WT) genotype, KIT oncoprotein is consistently overexpressed in these tumors. Certain clinicopathologic features, such as female predisposition, multifocal gastric location, and WT genotype suggest a relationship with Carney's triad.Although imatinib mesylate achieves a clinical response in >80% of adult patients with metastatic or advanced GIST, the efficacy of selective kinase inhibition in pediatric GIST population has not b...

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. It is our hypothesis following the melanoma model that mutations in BRAF or NRAS may play a role in wild-type GIST pathogenesis. Alterations in RAS/MEK/ERK pathway may also be involved in development of imatinib resistance in GIST, particularly in tumors lacking secondary KIT or PDGFRA mutations. Imatinib-naive wild-type GISTs from 61 patients, including 15 children and 28 imatinib-resistant tumors without secondary KIT mutations were analyzed. Screening for hot spots mutations in BRAF (exons 11 and 15) and NRAS (exons 2 and 3) was performed. A BRAF exon 15 V600E was identified in 3 of 61 GIST patients, who shared similar clinical features, being 49- to 55-years-old females and having their tumors located in the small bowel. The tumors were strongly KIT immunoreactive and had a high risk of malignancy. An identical V600E BRAF mutation was also identified in one of 28 imatinib resistant GIST lacking a defined mechanism of drug resistance. In conclusion, we identified a primary BRAF V600E mutations in 7% of adult GIST patients, lacking KIT/PDGFRA mutations. The BRAF-mutated GISTs show predilection for small bowel location and high risk of malignancy. A secondary V600E BRAF mutation could represent an alternative mechanism of imatinib resistance. Kinase inhibitors targeting BRAF may be effective therapeutic options in this molecular GIST subset.

Activating mutations in either BRAF or NRAS are seen in a significant number of malignant melanomas, but their incidence appears to be dependent to ultraviolet light exposure. Thus, BRAF mutations have the highest incidence in non-chronic sun damaged (CSD), and are uncommon in acral, mucosal and CSD melanomas. More recently, activating KIT mutations have been described in rare cases of metastatic melanoma, without further reference to their clinical phenotypes. This finding is intriguing since KIT expression is downregulated in most melanomas progressing to more aggressive lesions. In this study, we investigated a group of anal melanomas for the presence of BRAF, NRAS, KIT and PDGFRA mutations. A heterozygous KIT exon 11 L576P substitution was identified in 3 of 20 cases tested. The 3 KIT mutation-carrying tumors were strongly immunopositive for KIT protein. No KIT mutations were identified in tumors with less than 41 KIT immunostaining. NRAS mutation was identified in one tumor. No BRAF or PDGFRA mutations were identified in either KIT positive or negative anal melanomas. In vitro drug testing of stable transformant Ba/F3 KIT L576P mutant cells showed sensitivity for dasatinib (previously known as BMS-354825), a dual SRC/ABL kinase inhibitor, and imatinib. However, compared to an imatinib-sensitive KIT mutant, dasatinib was potent at lower doses than imatinib in the KIT L576P mutant. These results suggest that a subset of anal melanomas show activating KIT mutations, which are susceptible for therapy with specific kinase inhibitors. ' 2007 Wiley-Liss, Inc.Key words: melanoma; anal; mucosal; KIT; NRAS; BRAF mutations The KIT receptor tyrosine kinase plays a critical role in the normal development and function of the melanocytes during embryonic stage and in the postnatal organism.1,2 Loss-of-function mutations in KIT and its ligand result in white spotting phenotype in mice and humans. [3][4][5] In contrast, activating KIT mutations have been implicated in the pathogenesis of certain human malignancies, such as gastrointestinal stromal tumors, seminomas, mastocytomas, but were not reported until recently in patients with malignant melanoma. Furthermore, KIT expression, typically found in normal melanocytes, benign nevi and in situ melanoma, appears to be downregulated in invasive and metastatic melanomas.6 This progressive decrease in KIT immunopositivity is associated with increasing dermal invasiveness of the tumor. One hypothesis is that KIT signaling may be important in regulating cell differentiation and tissue morphogenesis, and therefore loss of its expression may be a required step in the course of tumor progression. 7 In this context, isolated reports of activating KIT mutations in melanoma patients, 8,9 are intriguing and suggest an alternative mechanism, in which constitutive activation of KIT through oncogenic mutations positively regulate mitogenesis and induces neoplastic transformation.The genetic alterations identified in melanomas at different sites and with different levels of sun exposure indi...