c-Abl is normally regulated by an autoinhibitory mechanism, the disruption of which leads to chronic myelogenous leukemia. The details of this mechanism have been elusive because c-Abl lacks a phosphotyrosine residue that triggers the assembly of the autoinhibited form of the closely related Src kinases by internally engaging the SH2 domain. Crystal structures of c-Abl show that the N-terminal myristoyl modification of c-Abl 1b binds to the kinase domain and induces conformational changes that allow the SH2 and SH3 domains to dock onto it. Autoinhibited c-Abl forms an assembly that is strikingly similar to that of inactive Src kinases but with specific differences that explain the differential ability of the drug STI-571/Gleevec/imatinib (STI-571) to inhibit the catalytic activity of Abl, but not that of c-Src.

Persistently activated or tyrosine-phosphorylated STAT3 (pSTAT3) is found in 50% of lung adenocarcinomas. pSTAT3 is found in primary adenocarcinomas and cell lines harboring somatic-activating mutations in the tyrosine kinase domain of EGFR. Treatment of cell lines with either an EGFR inhibitor or an src kinase inhibitor had no effect on pSTAT3 levels, whereas a pan-JAK inhibitor (P6) blocked activation of STAT3 and inhibited tumorigenesis. Cell lines expressing these persistently activated mutant EGFRs also produced high IL-6 levels, and blockade of the IL-6/gp130/JAK pathway led to a decrease in pSTAT3 levels. In addition, reduction of IL-6 levels by RNA interference led to a decrease in tumorigenesis. Introduction of persistently activated EGFR into immortalized breast epithelial cells led to tumorigenesis, IL-6 expression, and STAT3 activation, all of which could be inhibited with P6 or gp130 blockade. Furthermore, inhibition of EGFR activity in multiple cell lines partially blocked transcription of IL-6 and concurrently decreased production and release of IL-6. Finally, immunohistochemical analysis revealed a positive correlation between pSTAT3 and IL-6 positivity in primary lung adenocarcinomas. Therefore, mutant EGFR could activate the gp130/JAK/STAT3 pathway by means of IL-6 upregulation in primary human lung adenocarcinomas, making this pathway a potential target for cancer treatment.

The Poxviridae family members vaccinia and variola virus enter mammalian cells, replicate outside the nucleus and produce virions that travel to the cell surface along microtubules, fuse with the plasma membrane and egress from infected cells toward apposing cells on actin-filled membranous protrusions. We show that cell-associated enveloped virions (CEV) use Abl- and Src-family tyrosine kinases for actin motility, and that these kinases act in a redundant fashion, perhaps permitting motility in a greater range of cell types. Additionally, release of CEV from the cell requires Abl- but not Src-family tyrosine kinases, and is blocked by STI-571 (Gleevec), an Abl-family kinase inhibitor used to treat chronic myelogenous leukemia in humans. Finally, we show that STI-571 reduces viral dissemination by five orders of magnitude and promotes survival in infected mice, suggesting possible use for this drug in treating smallpox or complications associated with vaccination. This therapeutic approach may prove generally efficacious in treating microbial infections that rely on host tyrosine kinases, and, because the drug targets host but not viral molecules, this strategy is much less likely to engender resistance compared to conventional antimicrobial therapies.

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...

Amyloid-␤ (A␤) peptides, consisting mainly of 40 and 42 aa (A␤40 and A␤42, respectively), are metabolites of the amyloid precursor protein and are believed to be major pathological determinants of Alzheimer's disease. The proteolytic cleavages that form the A␤ N and C termini are catalyzed by ␤-secretase and ␥-secretase, respectively. Here we demonstrate that ␥-secretase generation of A␤ in an N2a cell-free system is ATP dependent. In addition, the Abl kinase inhibitor imatinib mesylate (Gleevec, or STI571), which targets the ATP-binding site of Abl and several other tyrosine kinases, potently reduces A␤ production in the N2a cell-free system and in intact N2a cells. Both STI571 and a related compound, inhibitor 2, also reduce A␤ production in rat primary neuronal cultures and in vivo in guinea pig brain. STI571 does not inhibit the ␥-secretase-catalyzed S3 cleavage of Notch-1. Furthermore, production of A␤ and its inhibition by STI571 were demonstrated to occur to similar extents in both Abl ؊/؊ and WT mouse fibroblasts, indicating that the effect of STI571 on A␤ production does not involve Abl kinase. The efficacy of STI571 in reducing A␤ without affecting Notch-1 cleavage may prove useful as a basis for developing novel therapies for Alzheimer's disease.