The low-molecular-weight phosphotyrosine phosphatase is a negative regulator of FcgammaRIIA-mediated cell activation

Activation of human platelets by cross-linking of the low-affinity receptor for immunoglobulin G (FcgammaRIIA) is initiated by Src kinase-mediated phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) within the receptor, but the identity of the enzyme responsible for its dephosphorylation and inactivation is unknown. Here we report that the 18-kDa low-molecular-weight phosphotyrosine phosphatase (LMW-PTP) is expressed in human platelets and undergoes subcellular redistribution upon FcgammaRIIA cross-linking. In vitro, LMW-PTP was found to efficiently dephosphorylate activated FcgammaRIIA and LAT, but not Syk or phospholipase Cgamma2. In the megakaryocytic cell line DAMI, antibody-induced phosphorylation of FcgammaRIIA was rapid and transient. The late dephosphorylation of FcgammaRIIA was dramatically delayed upon reduction of LMW-PTP expression by siRNA. Strikingly, overexpression of LMW-PTP resulted in the inhibition of antibody-induced phosphorylation of FcgammaRIIA, and caused a more rapid dephosphorylation. In addition, overexpression of LMW-PTP inhibited activation of Syk downstream of FcgammaRIIA and reduced intracellular Ca(2+) mobilization. These results demonstrate that LMW-PTP is responsible for FcgammaRIIA dephosphorylation, and is implicated in the down-regulation of cell activation mediated by this ITAM-bearing immunoreceptor.     

Primary nodal marginal zone B-cell lymphoma: clinical features and prognostic assessment of a rare disease

This study defined the clinical features and assessed the prognosis of 47 patients (17 males, 30 females, median age 63 years) with primary nodal marginal zone B-cell lymphoma. Forty-five per cent had stage IV disease. Hepatitis C virus serology was positive in 24%. According to the Follicular Lymphoma International Prognostic Index (FLIPI), 33% were classified as low-risk, 34% as intermediate-risk, and 33% as high-risk. The 5-year overall survival (OS) was 69%. In univariate analysis worse OS was associated with: FLIPI (P = 0.02), age > 60 years (P = 0.05) and raised lactate dehydrogenase (P = 0.05). In multivariate analysis, only FLIPI predicted a worse OS (P = 0.02).     

Potential histologic and molecular predictors of response to temsirolimus in patients with advanced renal cell carcinoma

PURPOSE: Similar to other molecularly targeted agents, temsirolimus, an inhibitor of mammalian target of rapamycin, has shown promising activity in advanced renal cell carcinoma. However, only a subset of patients appears to derive significant tumor responses. In an effort to identify potential predictors of response to temsirolimus, tumor samples from a subset of patients within a randomized phase II trial of temsirolimus in advanced renal cell carcinoma were studied. PATIENTS AND METHODS: Paraffin-embedded tissue sections from patients who had received temsirolimus were immunostained with antibodies to carbonic anhydrase IX, phospho-S6, phospho-Akt (pAkt), and phosphotase and tensin homologue. Expression levels were correlated with objective response (partial response [PR], minor response [MR]) and clinical benefit (PR, MR, SD>or=4 cycles) to temsirolimus. In addition, von Hippel-Lindau (VHL) mutational analysis was performed and correlated with response. RESULTS: Tissue specimens were obtained from 20 patients who were evaluable for both tumor response and staining for phospho-S6 and carbonic anhydrase IX. In addition, 19 specimens were evaluable for pAkt, and 18 for phosphotase and tensin homologue. VHL mutational analysis was performed on 16 samples. Five patients achieved an objective response (1 PR/4 MRs) to temsirolimus. There was a positive association of phospho-S6 expression (P=.02) and a trend toward positive expression of pAkt (P=.07) with response to temsirolimus. No patient without high expression of either phospho-S6 or pAkt experienced an objective tumor response. There was no correlation of carbonic anhydrase IX and phosphotase and tensin homologue expression or VHL status with response to temsirolimus. CONCLUSION: These results suggest that phospho-S6 and pAkt expression are promising predictive biomarkers for response to temsirolimus that are worthy of further exploration for use in patient selection models for mammalian target of rapamycin inhibitors.     

Gefitinib and bicalutamide show synergistic effects in primary cultures of prostate cancer derived from androgen-dependent naive patients

We previously demonstrated that the inhibition of the epidermal growth factor receptor (EGFR) signalling affects the endocrine therapy responses of prostate cancer (PCa) cells and that bicalutamide (BCLT) is able to reinforce PI3K activity through mechanisms involving PTEN decrement and EGFR and Her2 activities. The aim of this study was to evaluate if the hormonal therapy with BCLT can affect the EGFR-targeted therapy using primary cultures obtained from 22 human PCa tissues harvested after radical prostatectomy (RP) in patients who received (n=10) BCLT and those that did not (n=12) as neoadjuvant hormone therapy (NHT). We demonstrated that cultures derived from PCa tissues harvested after NHT presented significantly higher EGFR and Her2 levels compared to cultures derived from control patients. However, cultures derived from patients with NHT were less sensitive to gefitinib when compared to cultures derived from control patients. Conversely, BCLT effectiveness did not seem to be different in the two groups and was partially additive with gefitinib in the NHT group and additive/synergistic in the control group. Cultures (8/22) were negative for the expression of the PTEN gene and we observed no differences in the two groups. Thus the different IC50 values observed for gefitinib and the partial additivity in the combination treatment with gefitinib and BCLT is influenced by EGFR/Her2 ratio because it was shown that EGFR inhibition was lower when Her2 is overexpressed. Taken together, our results indicate that anti-EGFR targeted therapies and a possible combination therapy involving gefitinib and BCLT should be performed early in naive patients when Her2 is not overexpressed and before the anti-androgenic hormone therapy induces such an undesirable effect.