S. Komiya

A new protein containing an SH2 domain that inhibits JAK kinases

The proliferation and differentiation of cells of many lineages are regulated by secreted proteins known as cytokines. Cytokines exert their biological effect through binding to cell-surface receptors that are associated with one or more members of the JAK family of cytoplasmic tyrosine kinases. Cytokine-induced receptor dimerization leads to the activation of JAKs, rapid tyrosine-phosphorylation of the cytoplasmic domains, and subsequent recruitment of various signalling proteins, including members of the STAT family of transcription factors, to the receptor complex. Using the yeast two-hybrid system, we have now isolated a new SH2-domain-containing protein, JAB, which is a JAK-binding protein that interacts with the Jak2 tyrosine-kinase JH1 domain. JAB is structurally related to CIS, a cytokine-inducible SH2 protein,. Interaction of JAB with Jak1, Jak2 or Jak3 markedly reduces their tyrosine-kinase activity and suppresses the tyrosine-phosphorylation and activation of STATs. JAB and CIS appear to function as negative regulators in the JAK signalling pathway.

Cloning and characterization of APS, an adaptor molecule containing PH and SH2 domains that is tyrosine phosphorylated upon B-cell receptor stimulation

Stimulation of B lymphocytes through their antigen receptor (BCR) results in rapid increases in tyrosine phosphorylation of a number of proteins, which leads to a cascade of biochemical changes that initiates B cell proliferation and differentiation or growth inhibition. A novel cDNA, designed APS, encoding an adaptor protein with a Pleckstrin homology (PH) domain, Src homology 2 (SH2) domain, and a tyrosine phosphorylation site was cloned from a B cell cDNA library using a yeast two hybrid system. APS is structurally similar to SH2-B, an SH2 protein that potentially binds to the immunoreceptor tyrosine-based activation motif (ITAM) as well as Lnk which is postulated to be a signal transducer that links T-cell receptor to phospholipase Cγ, Grb2 and phosphatidylinositol 3-kinase. APS expressed only in human Burkitts lymphoma cells among cell lines we examined and tyrosine phosphorylated in response to BCR stimulation. APS bound to Shc irrespective of stimulation and bound to Grb2 after stimulation, suggesting that it plays a role in linkage from BCR to Shc/Grb2 pathway. These results indicate that APS, SH2-B and Lnk form a new adaptor family that links immune receptors to signaling pathways involved in tyrosine-phosphorylation.

APS, an adaptor protein containing Pleckstrin homology (PH) and Src homology-2 (SH2) domains inhibits the JAK-STAT pathway in collaboration with c-Cbl

We cloned a novel adaptor protein, APS (adaptor molecule containing Pleckstrin homology (PH) and Src Homology-2 (SH2) domains), which was tyrosine phosphorylated in response to c-kit or B cell receptor stimulation. Here, we report that APS was tyrosine phosphorylated by Janus kinase-2 (JAK2) at its C-terminal tyrosine residue and interacted with c-Cbl. Forced expression of APS in an erythropoietin (EPO)-dependent hematopoietic cell line resulted in reduced activation of STAT5 but not cell proliferation in response to EPO. APS bound to the phosphorylated tyrosine residue, Y343 of the erythropoietin receptor cytoplasmic domain. Co-expression of APS and c-Cbl, but not expression of either alone inhibited EPO-dependent STAT5 activation in 293 cells. This required the C-terminal phosphorylation site, as well as PH and SH2 domains of APS. Therefore, one of the major functions of APS is in recruitment of c-Cbl into the receptor/JAK complex, thereby inhibiting JAK signaling activity.

Cementation in the treatment of giant cell tumor of bone

SummaryThis study was designed to review the clinical experience of cementation in the treatment of giant cell tumor of bone and to clarify its biologic basis. Eleven patients treated by this technique had results rated excellent. No recurrences of the tumor were found. Serious complications, including infection, late fracture, or secondary osteoarthrosis, did not occur. The possibility of immediate fixation and stabilization of large defects is the most valuable point of this method. Local recurrence seems to be easily detectable by magnetic resonance imaging. A cell line of mononuclear cells from giant cell tumor of bone was examined for its response to hyperthermic exposure. Hyperthermic treatment was carried out at temperature of 60° for 10 min and in other conditions. The numbers of cells surviving after heat treatment were counted, and flow cytometry was used to analyze the positive rate of surface antigens of the cells and the pattern of DNA distribution at the different temperatures. The heat treatment caused a fair number of the cells to fall into S-phase, and the tetraploid value was very low. The higher the temperature and the longer the time, the fewer cells survived and the less the expression of the monocytic phenotype. No cells survived after heating at 60° for 10 min. Cementation seemed to have a hyperthermic effect to the cells of giant cell tumor of bone.

Prognostic factors in giant cell tumor of bone a modified histological grading system useful as a guide to prognosis

SummaryAn analysis of 26 patients with giant cell tumor of bone was carried out to determine the clinical and pathological factors affecting the prognosis of the tumor, with a follow-up program of more than 3 years. The physical characteristics of the pathological features were measured objectively using an image analyzer. A significant correlation between the therapeutic procedures and recurrence of the tumor was found, but no pathological variables were significantly correlated. Excision or resection en bloc should be performed for the initial treatment of the tumor. Local recurrence could not be predicted on the basis of histological grading. Stromal cell atypia was significantly correlated with metastasis, but multinucleated giant cells bore no correlation to either recurrence or metastasis. The use of a modified histological grading system based not on variations of the stroma and giant cells but only on the atypia of mononuclear stromal cells, either malignant or classical, is recommended for the clinical assessment of the tumor.

Histamine-stimulated production of matrix metalloproteinase 1 by human rheumatoid synovial fibroblasts is mediated by histamine H1-receptors

The purpose of this study was to investigate the role of histamine in human rheumatoid synovial fibroblasts in the production of factors responsible for tissue remodelling and cartilage breakdown in rheumatoid arthritis. We examined the effects of histamine of tritiated thymidine incorporation, production of matrix metalloproteinase-1 (MMP-1), histamine H1-receptor expression, phosphoinositide metabolism and intracellular calcium ion concentration ([Ca2+]i) in human rheumatoid synovial fibroblasts. Tritiated thymidine incorporation studies demonstrated that histamine markedly stimulated the proliferation of rheumatoid synovial fibroblasts. Immunofluorescence and Northern blot analyses revealed that proMMP-1 production was also stimulated by histamine. The levels of inositol phosphates and [Ca2+]i in the cells were elevated in response to histamine, indicating that the cells expressed histamine H1-receptors; and Northern blot analysis indicated that these H1-receptors were up-regulated by histamine. In in situ hybridization, large amounts of histamine H1-receptor mRNA were also detected in rheumatoid synovial tissue. These results suggest that the interaction between H1-receptor expression in rheumatoid synovial fibroblasts and histamine secretion by mast cells and macrophages in the affected sites is an important event responsible for tissue remodelling and joint destruction in rheumatoid arthritis.

Bone tumors in the pelvis presenting growth during pregnancy

Abstract Among 56 cases of a giant cell tumor of bone (GCT) and 52 cases of chondrosarcoma (CSA) in our series, four patients were discovered to have a tumor in the pelvic bone that grew in size during pregnancy. These four rare cases are described here. They include three cases of a GCT in the sacrum and one case of a CSA in the innominate bone. The dextran-coated charcoal assay and immunohistochemical techniques demonstrated the independence of these tumors from hormonal regulation despite the growth stimulated during pregnancy. It was concluded that the delay in detection of these tumors in the pelvis was just related to the opportunity afforded for unexpected growth during pregnancy. Surgical management was difficult due to the delay in tumor detection. The initial complaints such as pain, discomfort, or numbness around the pelvis were misinterpreted as symptoms of pregnancy. It should be kept in mind that during pregnancy, any pain or numbness in the pelvic region could be the direct result of a tumor in the pelvic bone.

Development of a solitary bone cyst--a report of a case suggesting its pathogenesis.

The origin and natural course of solitary bone cysts (SBC) still remain controversial. Knowledge of the process of cyst formation and enlargement would be helpful for investigating its pathogenesis. Only two papers have described a radiodense nidus of the diaphysis as a precursor. Their cases were unique in that the initial lesions were in the diaphysis and that the cysts did not abut onto the epiphyseal line. This study reports a case in a patient with a tiny erosive lesion in the endosteal surface of the humeral metaphysis, which developed expansively into a typical large cyst over 6 years. Serial roentgenograms taken every year demonstrated the process of cyst enlargement. This is the first longitudinal study of a case with SBC documented from its onset.

p21 and Parathyroid Hormone-Related Peptide in the Growth Plate

Abstract. It is essential for terminal chondrocytes to die before the conversion of calcified cartilage to bone. We have previously demonstrated that apoptosis occurred in the terminal hypertrophic chondrocyte of the growth plate. However, the essential mechanism by which the differentiation of chondrocytes is regulated has not yet been characterized. The purpose of this study was to investigate the mechanism for regulating chondrocyte differentiation. We focused on PTHrP and p21 which regulated the differentiation of chondrocytes and investigated how these factors interacted with each other in chondrocyte differentiation in the growth plate. PTHrP was strongly positive on immunostaining at the interface between the proliferating and the upper zone of the hypertrophic chondrocytes, whereas p21 was negative. On the other hand, p21 was positive in the lower zone of hypertrophic chondrocytes. Furthermore, PTHrP up-regulated the cell proliferation and down-regulated the expression of the p21 messengers in SW-1353 chondrosarcoma cells. These findings indicated that PTHrP might be a negative regulator for p21 in the differentiation of chondrocytes.