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T Kurosaki

Publications and source records attributed to T Kurosaki.

At least 19 recordsLinked to original sources
PubMed2001

BLNK mediates Syk-dependent Btk activation.

Btk is a critical molecule in B cell antigen receptor (BCR)-coupled signaling, and its activity is regulated by Lyn and Syk. Although the molecular mechanism of Lyn-dependent Btk activation has been investigated, that of Syk-dependent Btk activation has remained unidentified. We have demonstrated that BLNK mediates Syk-dependent Btk activation. In a reconstitution cell system, coexpression of BLNK allows Syk to phosphorylate Btk on its tyrosine 551, leading to the enhancement of Btk activity. This phosphorylation depends on the interaction of Btk and BLNK by means of the Btk-Src homology 2 domain. The existence of such an activation mechanism is supported by the observation that the BCR-induced Btk phosphorylation and activation are significantly reduced in BLNK-deficient B cells as well as in Syk-deficient B cells. Although previous observations have identified the function of BLNK as the linker that integrates the action of Btk and Syk into downstream effectors such as phospholipase Cgamma2, our present study indicates another function of BLNK that connects the activity of Syk to that of Btk.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Negative control of store-operated Ca2+ influx by B cell receptor cross-linking.

An increase in the intracellular Ca(2+) concentration by B cell receptor (BCR) cross-linking plays important roles in the regulation of B cell functions. [Ca(2+)](i) is regulated by Ca(2+) release from the Ca(2+) store as well as store-operated Ca(2+) influx (SOC). Protein tyrosine kinases downstream of BCR cross-linking were shown to regulate the mechanism for Ca(2+) release. However, it remains elusive whether BCR cross-linking regulates SOC or not. In this study, we examined the effect of BCR cross-linking on thapsigargin-induced SOC in the DT40 B cells. We found that the SOC-mediated increase in intracellular Ca(2+) concentration was inhibited by BCR cross-linking. Using a membrane-potential-sensitive dye, we found that BCR cross-linking induced depolarization, which is expected to decrease the driving force of Ca(2+) influx and SOC channel conductance. When membrane potential was held constant by the transmembrane K(+) concentration gradient in the presence of valinomycin, the BCR-mediated inhibition of SOC was still observed. Thus, the BCR-mediated inhibition of SOC involves both depolarization-dependent and depolarization-independent mechanisms of SOC inhibition. The depolarization-independent inhibition of the SOC was abolished in Lyn-deficient, but not in Bruton's tyrosine kinase-, Syk- or SHIP (Src homology 2 domain containing phosphatidylinositol 5'-phosphatase)-deficient cells, indicating that Lyn is involved in the inhibition. These results show novel pathways of BCR-mediated SOC regulations.

Animals↗
PubMed2001

Independent association of angiogenesis index with outcome in prostate cancer.

New molecular factors have been characterized that are associated with the prognosis of prostate carcinoma patients, including p53 status and angiogenesis. We reported recently that mutant p53 (mp53) was associated with decreased expression of an endogenous inhibitor of angiogenesis, thrombospondin-1 (TSP-1), and increased microvessel density in melanoma and breast cancer. In this study, we performed a similar analysis on primary prostate carcinoma to determine whether these factors were associated with each other or patient outcomes. Paraffin-embedded specimens of 98 cases of primary prostate carcinoma were obtained and examined to confirm tissue diagnosis and Gleason scores. Carcinoma-specific levels of p53, TSP-1, and tumor angiogenesis were determined using semiquantitative immunohistochemistry (IHC) methods. Acquisition of mp53 was significantly associated with decreased TSP-1 (P = 0.002) and increased angiogenesis (P < 0.0001). An angiogenesis index integrating mp53, TSP-1, and angiogenesis (CD31) scores was found to be an independent predictor of survival in univariate and multivariate analyses that included Gleason score, clinical stage, and patient age. Further validation of the angiogenesis index in prostate carcinoma may provide a new tool to stratify patient risk.

Adenocarcinoma↗
PubMed2000

Asian patients with gastric carcinoma in the United States exhibit unique clinical features and superior overall and cancer specific survival rates.

BACKGROUND: The 5-year survival rate from gastric carcinoma, stratified by stage, is markedly greater in the Far East than in the United States. This survival rate advantage may reflect differences in diagnostic criteria, more complete staging, more radical surgery, or less aggressive tumor biology. METHODS: A historic cohort of consecutive cases of gastric carcinoma reported to the population-based California Cancer Registries of Orange, San Diego and Imperial Counties from 1984 to 1996 was studied. Factors associated with Asian race were profiled using logistic regression. Multivariate survival analyses were performed using a Cox proportional hazard model. RESULTS: Two thousand four hundred sixteen patients (64%) were non-Latino white; 690 (18%) were Latino; 94 (2.5%) were black; 541 (14%) were of Asian descent: Korean (22%), Vietnamese (20%), Japanese (20%), Chinese (14%), and Filipino (12%). Asian patients were more likely to have localized (lymph node negative) disease (odds ratio [OR], 1.61; 95% confidence interval [CI], 1.23-2.10), less likely to have tumors of the gastroesophageal junction (OR, 0.22; 95% CI, 0.15-0.31,), and less likely to be older than 50 years (OR, 0.58; 95% CI, 0.43-0.77). Asian patients with gastric carcinoma were twice as likely as non-Latino whites to be alive at 5 years (20.9% vs. 10.2%; P < 0.0001). Multivariate analyses indicated that whites had an increased risk of dying from all causes (relative risk [RR], 1.34; 95% CI, 1.16-1.55; P < 0.01) and of dying from cancer in comparison to Asian patients (RR, 1.26; 95% CI, 1.07-1.48; P < 0.05). CONCLUSIONS: Asians who received a diagnosis of gastric carcinoma in the United States have less advanced disease than non-Asians. The increased proportion of localized disease and improved survival rates of patients of Asian descent in the United States is consistent with less aggressive tumor biology.

Adult↗
PubMed2000

Functional complementation of BLNK by SLP-76 and LAT linker proteins.

Recent studies have demonstrated a requirement for the SLP-76 (SH2 domain-containing leukocyte protein of 76 kDa) and LAT (linker for activation of T cells) adaptor/linker proteins in T cell antigen receptor activation and T cell development as well as the BLNK (B cell linker) linker protein in B cell antigen receptor (BCR) signal transduction and B cell development. Whereas the SLP-76 and LAT adaptor proteins are expressed in T, natural killer, and myeloid cells and platelets, BLNK is preferentially expressed in B cells and monocytes. Although BLNK is structurally homologous to SLP-76, BLNK interacts with a variety of downstream signaling proteins that interact directly with both SLP-76 and LAT. Here, we demonstrate that neither SLP-76 nor LAT alone is sufficient to restore the signaling deficits observed in BLNK-deficient B cells. Conversely, the coexpression of SLP-76 and LAT together restored BCR-inducible calcium responses as well as activation of all three families of mitogen-activated protein kinases. Together, these data suggest functional complementation of SLP-76 and LAT in T cell antigen receptor function with BLNK in BCR function.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Involvement of LAT, Gads, and Grb2 in compartmentation of SLP-76 to the plasma membrane.

B cell linker protein (BLNK) and Src homology 2 domain-containing leukocyte protein of 76 kD (SLP-76) are adaptor proteins required for B cell receptor (BCR) and T cell receptor function, respectively. Here, we show that expression of SLP-76 cannot reconstitute BCR function in Zap-70(+)BLNK(-) B cells. This could be attributable to inability of SLP-76 to be recruited into glycolipid-enriched microdomains (GEMs) after antigen receptor cross-linking. Supporting this idea, the BCR function was restored when a membrane-associated SLP-76 chimera was enforcedly localized to GEMs. Moreover, we demonstrate that addition of both linker for activation of T cells (LAT) and Grb2-related adaptor downstream of Shc (Gads) to SLP-76 allow SLP-76 to be recruited into GEMs, whereby the BCR function is reconstituted. The Gads function was able to be replaced by overexpression of Grb2. In contrast to SLP-76, BLNK did not require Grb2 families for its recruitment to GEMs. Hence, these data suggest a functional overlap between BLNK and SLP-76, while emphasizing the difference in requirement for additional adaptor molecules in their targeting to GEMs.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Cutting edge: essential role of phospholipase C-gamma 2 in B cell development and function.

Cross-linking of the B cell Ag receptor (BCR) induces the tyrosine phosphorylation of multiple cellular substrates, including phospholipase C (PLC)-gamma 2, which is involved in the activation of the phosphatidylinositol pathway. To assess the importance of PLC-gamma 2 in murine lymphopoiesis, the PLC-gamma 2 gene was inducibly ablated by using IFN-regulated Cre recombinase. Mice with a neonatally induced loss of PLC-gamma 2 function displayed reduced numbers of mature conventional B cells and peritoneal B1 cells and defective responses in vitro to BCR stimulation and in vivo to immunization with thymus-independent type II Ags. In contrast, T cell development and TCR-mediated proliferation were normal. Taken together, PLC-gamma 2 is a critical component of BCR signaling pathways and is required to promote B cell development.

Animals↗
PubMed2000

B cell antigen receptor-induced activation of Akt promotes B cell survival and is dependent on Syk kinase.

Signaling through the B cell Ag receptor (BCR) is a key determinant in the regulation of B cell physiology. Depending on additional factors, such as microenvironment and developmental stage, ligation of the BCR can trigger B lymphocyte activation, proliferation, or apoptosis. The regulatory mechanisms determining B cell apoptosis and survival are not known. Using the chicken B lymphoma cell line DT40 as a model system, we investigated the role of the serine/threonine kinase Akt in B cell activation. While parental DT40 cells undergo apoptosis in response to BCR cross-linking, cells overexpressing Akt show a greatly diminished apoptotic response. By contrast, limiting the activation of Akt, either by inhibiting phosphatidylinositol 3-kinase or by ectopic expression of the phospholipid phosphatase MMAC1, results in a significant increase in the percentage of apoptotic cells after BCR cross-linking. Using various DT40 knockout cell lines, we further demonstrate that the tyrosine kinase Syk is required for Akt activation and that Lyn tyrosine kinase inhibits Akt activation. Taken together, the data demonstrate that Akt plays an important role in B cell survival and that Akt is activated in a Syk-dependent pathway.

Animals↗
PubMed2000

Cbl suppresses B cell receptor-mediated phospholipase C (PLC)-gamma2 activation by regulating B cell linker protein-PLC-gamma2 binding.

Accumulating evidence indicates that the Cbl protein plays a negative role in immune receptor signaling; however, the mode of Cbl action in B cell receptor (BCR) signaling still remains unclear. DT40 B cells deficient in Cbl showed enhanced BCR-mediated phospholipase C (PLC)-gamma2 activation, thereby leading to increased apoptosis. A possible explanation for the involvement of Cbl in PLC-gamma2 activation was provided by findings that Cbl interacts via its Src homology 2 (SH2) domain with B cell linker protein (BLNK) after BCR ligation. BLNK is a critical adaptor molecule for PLC-gamma2 tyrosine phosphorylation through its binding to the PLC-gamma2 SH2 domains. As a consequence of the interaction between Cbl and BLNK, the BCR-induced recruitment of PLC-gamma2 to BLNK and the subsequent PLC-gamma2 tyrosine phosphorylation were inhibited. Thus, our data suggest that Cbl negatively regulates the PLC-gamma2 pathway by inhibiting the association of PLC-gamma2 with BLNK.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Involvement of Shc and Cbl-PI 3-kinase in Lyn-dependent proliferative signaling pathways for G-CSF.

Granulocyte colony-stimulating factor (G-CSF) is the major hematopoietic factor which controls the production and differentiation of granulocytes. The G-CSF receptor (G-CSFR) belongs to the superfamily of the cytokine receptors, which transduce signals via the activation of cytosolic protein tyrosine kinases (PTK). To determine the role of specific PTK in G-CSF signaling we expressed the human G-CSFR in cell lines derived from DT40 B cells, which lack either the Src-related Lyn or Syk. Wild-type (wt) and syk-deficient cells underwent increased DNA synthesis in response to G-CSF; lyn-deficient cells did not. The purpose of these studies is to identify Lyn's downstream effectors in mediating DNA synthesis. While G-CSF stimulated Ras activity in all cell lines, G-CSF failed to induce the tyrosine phosphorylation of Shc in lyn-deficient cells. G-CSF induced a statistically significant activation of Erk1/Erk2 Kinase or p90Rsk only in the wt cells. G-CSF induced the tyrosine phosphorylation of Cbl and increased activity of PI 3-kinase in wild-type and syk-deficient, but non in lyn-deficient, cells. Inhibition of Shc by over-expression of its SH2 or PTB domains or PI 3-kinase by either treatment with wortmannin or expression of the CblY731F mutant decreased G-CSF-induced DNA synthesis. Thus, the Lyn, Cbl-PI 3-kinase, and Shc/non-Ras-dependent pathways correlate with the ability of cells to respond to G-CSF with increased DNA synthesis.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Functional dissection of BCR signaling pathways.

Signal transduction by the BCR is critical for progression through developmental checkpoints as well as for immune responses. Recent results obtained in mice deficient either in an adaptor molecule, BLNK (alternatively named SLP-65 or BASH), or in phosphatidylinositol 3-kinase have revealed similar - though not identical - phenotypes to those of Btk(-/-) mice, suggesting a functional link between BLNK, Btk and phosphatidylinositol 3-kinase.

Adaptor Proteins, Signal Transducing↗
PubMed2000

BCAP: the tyrosine kinase substrate that connects B cell receptor to phosphoinositide 3-kinase activation.

Tyrosine phosphorylation of adaptor proteins permits the B cell antigen receptor (BCR)-associated protein tyrosine kinases to regulate downstream effector molecules. Here, we report the identification of a novel B cell adaptor for phosphoinositide 3-kinase (PI3K), termed BCAP. Tyrosine phosphorylation of BCAP is mediated by Syk and Btk, thereby providing binding site(s) for the p85 subunit of PI3K. Disruption of the BCAP gene in the DT40 B cell line inhibits BCR-mediated phosphatidylinositol 3,4,5-trisphosphate generation, leading to impaired Akt response. Moreover, recruitment of PI3K to glycolipid-enriched microdomains (GEMs) is significantly attenuated in the absence of BCAP. Hence, these data suggest that BCAP bridges BCR-associated kinases to the PI3K pathway by regulating PI3K localization.

Adaptor Proteins, Signal Transducing↗
PubMed2000

HPK1 is activated by lymphocyte antigen receptors and negatively regulates AP-1.

The serine/threonine kinase HPK1 is a member of the germinal center kinase (GCK) family that has been implicated in the regulation of MAP kinase pathways. Here, we demonstrate the involvement of HPK1 in antigen receptor signaling. Engagement of the TCR or the BCR resulted in a marked induction of HPK1 catalytic activity. Subsequent analysis revealed that Src and Syk/ZAP-70 tyrosine kinases and the adaptor proteins LAT, SLP-76, BLNK, Grb2, and Grap are involved in HPK1 activation. Overexpression of HPK1 inhibited TCR activation of AP-1 and ERK2, whereas the kinase-inactive mutant of HPK1 potentiated these responses. Neither form of HPK1 affected PMA or v-Ras activation of AP-1 and ERK2. Thus, HPK1 is a negative regulator of the TCR-induced AP-1 response pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Regulation of the phospholipase C-gamma2 pathway in B cells.

In B lymphocytes, a signaling complex that contributes to cell fate decisions is the B-cell antigen receptor (BCR), with different extents of receptor engagement leading to such outcomes as cell death, survival, or proliferation. Here, based upon the available genetic and biochemical data of the BCR signal components, we discuss several mechanisms by which BCR signals are propagated and modified, with specific emphasis on the phospholipase C (PLC)-gamma2-calcium pathway Gene-targeting experiments in DT40 chicken B cells highlighted the importance of the intracellular protein tyrosine kinases Syk and Btk in PLC-gamma2 activation. Until recently, the molecular mechanism underlying the double requirement for Syk and Btk in PLC-gamma2 activation remained unclear, but new data suggest that an adapter molecule, B-cell linker protein (alternatively named SLP-65 or BASH), phosphorylated by Syk, provides docking sites for Btk SH2 domain as well as PLC-gamma2 SH2 domains, thus bringing Btk into close proximity with PLC-gamma2. The activated Btk then phosphorylates PLC-gamma2, leading to its activation. The activated PLC-gamma2 converts phosphatidylinositol 4,5-bisphosphate into the second messenger inositol 1,4,5-trisphosphate (IP3), which in turn binds to IP3 receptors located on the endoplasmic reticulum (ER). Binding of IP3 to the IP3 receptors is essential for triggering a calcium release from the ER and subsequent entry of extracellular calcium. Balancing these activation signals in the PLC-gamma2-calcium pathway are the inhibitory receptors expressed on B cells, FcyRII and paired immunoglobin-like receptor (PIR)-B. Although both FcyRII and PIR-B inhibits the BCR-mediated [Ca2+]i increase, the inhibitory mechanisms of these receptors are distinct. The FcyRII-mediated inhibitory signal is dependent on lipid phosphatase SHIP, whereas the PIR-B requires redundant functions of protein phosphatases SHP-1 and SHP-2. Thus, PIR-B and FcgammaRII inhibit calcium signals by utilizing two distinct signaling molecules, thereby contributing to setting threshold levels for activation signals as well as terminating activation responses.

Animals↗
PubMed2000

[A trial of amantadine for the treatment of influenza A infection in children].

We administered amantadine to 52 children for therapy and 3 children for prophylaxis of influenza A infection from January to March 1998. Among the 23 children in the therapy group with proven influenza A/H3N2 infection, 15 patients (60%) allayed fever within 3 days but 9 (40%) had persistent fever for more than 4 days after administration of amantadine. Seven of these nine patients (40%) received amantadine within 2 days after the onset of fever. Two of these nine had secondary bacterial infections. One child had insomnia as side effect. We concluded that administration of amantadine for therapy is safe and effective, if given to patients without secondary bacterial infections in the first 48 hours of the illness.

Adolescent↗
PubMed2000

Cancer risk estimates for family members of a population-based family registry for breast and ovarian cancer.

Population-based breast and ovarian cancer family registries can facilitate studies to evaluate genetic and environmental factors in the etiology of these malignancies. The purpose of this study is to describe what is, as far as we know, the first population-based breast and ovarian cancer family registry and to estimate breast and ovarian cancer risk in relatives of breast and ovarian cancer probands. Population-based consecutive incident cases of breast and ovarian cancer were invited to participate in the University of California, Irvine breast and ovarian family registry. In this study, we report data on 1567 breast cancer and 328 ovarian cancer probands. The operational components of this family registry include enrollment of probands, family history interviewing, confidentiality, pathology, verification and review, biospecimen bank, statistical/genetic analysis, and special studies on positional cloning of known genes. All of the components are tracked through the University of California, Irvine Genetic Research Information System. In non-Hispanic-white breast cancer probands, relative risk (RR) of breast cancer in mothers and sisters is significantly elevated [RR = 1.7 and 95% confidence interval (CI) = 1.4-2.0 and RR = 2.8 and 95% CI = 2.3-3.3, respectively]. In families of ovarian cancer probands, mothers are at increased risk of ovarian cancer (RR = 4.6; 95% CI, 2.1-8.7). RR of breast cancer in mothers of Hispanic breast cancer probands is significantly elevated (RR = 4.9; 95% CI, 2.6-8.5). No elevation of breast or ovarian cancer risk was observed among relatives of Asian probands. In general, there is a decrease in RR among mothers and sisters with increase in age of onset of probands. In second-degree relatives and first cousins, the breast cancer hazards ratios increase with increase in the number of affected first-degree relatives and decrease with increase in age at onset of the proband.

Adult↗
PubMed1999

Tyrosine phosphorylation of shc in response to B cell antigen receptor engagement depends on the SHIP inositol phosphatase.

Tyrosine phosphorylation of Shc in response to B cell Ag receptor (BCR) engagement creates binding sites for the Src homology 2 (SH2) domain of Grb2. This facilitates the recruitment of both Grb2. Sos complexes and Grb2. SHIP complexes to the plasma membrane where Sos can activate Ras and SH2 domain-containing inositol phosphatase (SHIP) can dephosphorylate phosphatidylinositol 3,4,5-trisphosphate. Given the importance of Shc phosphorylation, we investigated the mechanism by which the BCR stimulates this response. We found that both the SH2 domain and phosphotyrosine-binding (PTB) domain of Shc are important for BCR-induced tyrosine phosphorylation of Shc and the subsequent binding of Grb2 to Shc. The unexpected finding that the PTB domain of Shc is required for Shc phosphorylation was investigated further. Because the major ligand for the Shc PTB domain is SHIP, we asked whether the interaction of Shc with SHIP was required for BCR-induced tyrosine phosphorylation of Shc. Using SHIP-deficient DT40 cells, we show that SHIP is necessary for the BCR to induce significant levels of Shc tyrosine phosphorylation. BCR-induced tyrosine phosphorylation of Shc could be restored in the these cells by expressing wild-type SHIP but not by expressing a mutant form of SHIP that cannot bind to Shc. This suggests that BCR-induced tyrosine phosphorylation of Shc may depend on the binding of SHIP to the Shc PTB domain. Thus, we have described a novel role for SHIP in BCR signaling, promoting the tyrosine phosphorylation of Shc.

Adaptor Proteins, Signal Transducing↗