Summary The eradication of Helicobacter pylori often leads to platelet recovery in patients with chronic idiopathic thrombocytopenic purpura (cITP). Although this clinical observation suggests the involvement of H. pylori, little is known about the pathogenesis of cITP. We initially examined the effect of H. pylori eradication on platelet counts in 20 adult Japanese cITP patients. Then, using platelet eluates as the probe in immunoblot analyses, we examined the role of molecular mimicry in the pathogenesis of cITP. Helicobacter pylori infection was detected in 75% (15 of 20) of cITP patients. Eradication was achieved in 13 (87%) of the H. pylori‐positive patients, seven (54%) of which showed increased platelet counts within the 4 months following treatment. Completely responsive patients also showed significant declines in platelet‐associated immunoglobulin G (PAIgG) levels. Platelet eluates from 12 (nine H. pylori‐positive and three H. pylori‐negative) patients recognized H. pylori cytotoxin‐associated gene A (CagA) protein, and in three completely responsive patients, levels of anti‐CagA antibody in platelet eluates declined after eradication therapy. Cross‐reactivity between PAIgG and H. pylori CagA protein suggests that molecular mimicry by CagA plays a key role in the pathogenesis of a subset of cITP patients.

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MEK kinase 1 (MEKK1) has been shown to contribute to the regulation of cell migration, whereas focal adhesion kinase (FAK) is a major player involved in both cell migration and integrin signaling. Here we show that MEKK1 and FAK are co-immunoprecipitated from mouse fibroblasts. Moreover, the association between MEKK1 and FAK appears to be physiologically relevant, as it is enhanced by treatment with epidermal growth factor (EGF). Targeting FAK to the membrane also enhanced its association with MEKK1, indicating that MEKK1 is localized to a membrane-related subcellular domain, perhaps focal adhesions. Interestingly, the expression of insulin receptor substrate-1 (IRS-1) was diminished in MEKK1-deficient fibroblasts, which is similar to an earlier finding in FAK-deficient fibroblasts. Insulin-like growth factor 1 (IGF-1)-induced ERK activation was diminished in MEKK1-deficient cells, but MEKK11 is a 196-kDa serine-threonine kinase activated in response to a variety of stimuli, including EGF, lysophosphatidic acid, osmotic stress, and microtubule toxins (1, 2). Upon activation, MEKK1 participates in the regulation of the JNK and ERK pathways and is involved in the activation of . In addition, MEKK1 senses microtubule integrity, protects cells from committing to apoptosis, and contributes to the migration of fibroblasts and epithelial cells. The phenotype of the MEKK1-null mouse includes an eyelid closure defect that is also seen in mice lacking the EGF receptor and TGF-␣ (6). This suggests the possibility that MEKK1 is required for EGF receptor control of cell migration. Consistent with that idea, overexpression of MEKK1 induces the formation of a large lamellipodia-like structure in epithelial cells (6). Still, the mechanism by which MEKK1 influences cell motility remains unclear.FAK is protein tyrosine kinase found at sites of adhesion (7). It is activated by integrin-mediated adhesion and serves as a signaling protein within cytoskeleton-associated networks (7). The Src-family protein tyrosine kinases p130 Cas, Shc, and Grb2 act in concert with FAK to transduce integrin-generated signals to the ERK/JNK MAP kinase cascades (7). Experiments using FAK-deficient cells have established that FAK is essential for integrin-stimulated cell migration and important for linking activation of the PDGF and EGF receptors to the cellular machinery that promotes directed cell migration (8). The fact that MEKK1 is enriched in membranes and colocalizes with ␣-actinin along actin stress fibers at focal adhesions (9, 10) prompted us to investigate the possibility that MEKK1 is associated with FAK.Insulin and IGF-1 exert diverse biological effects by binding to and activating their cognate tyrosine kinase receptors. IRS-1 is a major substrate for the insulin and IGF-1 receptors, which rapidly phosphorylate it on multiple tyrosine residues upon ligand binding. Recently, it was reported that targeted disruption of FAK eliminates IRS-1 expression in MEFs and that interactions between cells and the extracellular matrix regulate the tran...

BCR-ABL oncogene, the molecular hallmark of chronic myelogenous leukemia, arises in a primitive hematopoietic stem cell that has the capacity for both differentiation and self-renewal. Its product, Bcr-Abl protein, has been shown to activate signal transducers and activators of transcription 3 (STAT3) and to promote self-renewal in embryonic stem (ES) cells, even in the absence of leukemia inhibitory factor (LIF). MEK kinase 1 (MEKK1) is a 196-kDa mitogen-activated protein kinase (MAPK) kinase kinase involved in Bcr-Abl signal transduction. To investigate the role of MEKK1 in Bcr-Abl-induced transformation of stem cells, p210 Bcr-Abl was stably transfected into wildtype (WT p210 ) and MEKK1À/À (MEKK1À/À p210 ) ES cells. Bcr-Abl enhanced MEKK1 expression in ES transfectants, as it does in other Bcr-Abl-transformed cells. In the absence of LIF, WT p210 cells showed constitutive STAT3 activation and formed rounded, compact colonies having strong alkaline phosphatase activity, a characteristic phenotype of undifferentiated ES cells. MEKK1À/À p210 cells, by contrast, showed less STAT3 activity than WT p210 cells and formed large, flattened colonies having weak alkaline phosphatase activity, a phenotype of differentiated ES cells. These results indicate that MEKK1 plays a key role in Bcr-Ablinduced STAT3 activation and in ES cells' capacity for LIF-independent self-renewal, and may thus be involved in Bcr-Abl-mediated leukemogenesis in stem cells.

Myeloproliferative neoplasms (MPNs) constitute a group of phenotypically diverse chronic myeloid malignancies, characterized by clonal hematopoiesis and excessive production of terminally differentiated myeloid blood cells. The MPNs include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), most of which are characterized by a somatic point mutation, V617F, in the janus kinase 2 (JAK2) gene. This mutation was recently shown to occur more frequently in a specific JAK2 haplotype, JAK2 46/1, in North American and European MPN patients. Little is known, however, about JAK2 haplotypes in Japanese MPN patients. Therefore, we examined 108 Japanese patients with MPN, including 19 with PV, 61 with ET, 10 with PMF, and 17 with unclassifiable MPN, as well as 104 control individuals for the JAK2 rs10974944(C/G) single nucleotide polymorphism, in which the G allele indicates the 46/1 haplotype. We found that the JAK2 46/1 haplotype was significantly more frequent in patients with V617F-positive MPN than in controls (odds ratio [OR], 3.6; 95 % confidence interval [CI], 2.2-5.8, p < 0.001), and in PV patients than in controls (OR, 6.3; 95 % CI, 3.0-29.4, p < 0.001). In conclusion, we demonstrated that the JAK2 46/1 haplotype is associated with JAK2 V617F-positive MPNs in Japanese patients.