Tyr Phosphatase-Mediated P-ERK Inhibition Suppresses Senescence in EIA + v-raf Transformed Cells,Which, Paradoxically,Are Apoptosis-Protected in a MEK-Dependent Manner

Activation of the Ras-Raf-extracellular signal-regulated kinase (ERK) pathway causes not only proliferation and suppression of apoptosis but also the antioncogenic response of senescence. How these contrasting effects are reconciled to achieve cell transformation and cancer formation is poorly understood. In a system of two-step carcinogenesis (dedifferentiated PC EIA, transformed PC EIA-polyoma-middle T [PC EIA + Py] and PC EIA-v-raf [PC EIA + raf] cells], v-raf cooperated with EIA by virtue of a strong prosurvival effect, not elicited by Py-middle T, evident toward serum-deprivation-and H₂O₂-induced apoptosis. Apoptosis was detected by DNA fragmentation and annexin V staining. The prosurvival function of v-raf was, in part, mitogen-activated protein kinase/ERK kinase (MEK)-dependent, as shown by pharmacological MEK inhibition. The MEK-dependent antiapoptotic effect of v-raf was exerted despite a lower level of P-ERK1/2 in EIA + raf cells with respect to EIA + Py/EIA cells, which was dependent on a high tyrosine phosphatase activity, as shown by orthovanadate blockade. An ERK1/2 tyrosine phosphatase was likely involved. The high tyrosine phosphatase activity was instrumental to the complete suppression of senescence, detected by β-galactosidase activity, because tyrosine phosphatase blockade induced senescence in EIA + raf but not in EIA + Py cells. High tyrosine phosphatase activity and evasion from senescence were confirmed in an anaplastic thyroid cancer cell line. Therefore, besides EIA, EIA + raf cells suppress senescence through a new mechanism, namely, phosphatase-mediated P-ERK1/2 inhibition, but, paradoxically, retain the oncogenic effects of the Raf-ERK pathway. We propose that the survival effect of Raf is not a function of absolute P-ERK1/2 levels at a given time but is rather dynamically dependent on greater variations after an apoptotic stimulus.     

Randomized phase III clinical trial evaluating weekly cisplatin for advanced epithelial ovarian cancer

This randomized, open label, phase III clinical trial (1988-1992) compared the efficacy and safety of a dose-dense regimen of single-agent cisplatin with a standard 3-weekly schedule in first-line chemotherapy for advanced epithelial ovarian cancer. Two hundred eighty-five patients were randomly assigned to the experimental dose-dense arm (cisplatin 50 mg/m(2) weekly × nine cycles) or to the control (standard treatment) arm (cisplatin 75 mg/m(2), administered on day 1 every 21 days × six cycles). The primary outcome was progression-free survival (PFS). Secondary outcomes were overall survival (OS), overall response to chemotherapy, and toxicity. Toxicity and response to treatment were compared with the χ(2) test using trend or exact correction. PFS and OS were estimated by Kaplan-Meier analyses and treatment hazard ratios (HRs) with the Cox proportional hazards model. All statistical tests were two-sided. After a median follow-up of 16.8 years, no differences were observed between the two treatments in PFS (experimental arm: 17.2 months; control arm: 18.1 months; HR = 1.08, 95% confidence interval [CI] = 0.83 to 1.40; P = .57) and in OS (experimental arm: 35 months; control arm: 32 months; HR = 0.97, 95% CI = 0.75 to 1.26; P = .97). Thus, increasing dose intensity of cisplatin does not improve PFS or OS compared with standard chemotherapy.     

The Cu,Zn superoxide dismutase in neuroblastoma SK-N-BE cells is exported by a microvesicles dependent pathway

The antioxidant enzyme Cu,Zn superoxide dismutase has so far been considered costitutively expressed and exclusively localized into cytosol. In this paper we investigated Cu,Zn superoxide dismutase export in neuroblastoma SK-N-BE cells by flow cytometry analysis, confocal immunofluorescence analysis and enzyme-linked immunosorbed assay. Immunofluorescence analysis shows that the enzyme is exported by microvesicular granules; moreover the treatment of cells with brefeldin A and with 2-deoxy-D-glucose and sodium azide strongly decreases the amount of CuZn superoxide dismutase detected in the medium. Therefore the involvement of ATP-dependent mechanisms, likely including BFA-sensitive intracytoplasmic vesicles in Cu,Zn SOD export from SK-N-BE cells, has to be hypothesized. Microvesicular-mediated Cu,Zn SOD export in neurons could represent a relevant phenomenon able to influence cell excitability that is affected by reactive oxygen species.     

v-ras and protein kinase C dedifferentiate thyroid cells by down-regulating nuclear cAMP-dependent protein kinase A.

Ras proteins are membrane-associated transducers of eternal stimuli to unknown intracellular targets. The constitutively activated v-ras oncogene induces dedifferentiation in thyroid cells. v-Ras appears to act by stimulating protein kinase C (PKC), which inhibits the nuclear migration of the catalytic subunit of the cAMP-dependent protein kinase A (PKA). Nuclear tissue-specific and housekeeping trans-acting factors that are dependent on phosphorylation by PKA are thus inactivated. Exclusion of the PKA subunit from the nucleus could represent a general mechanism for the pleiotropic effects of Ras and PKC on cellular growth and differentiation.     

Aminopeptidases in the gonads of male and female rats

OBJECTIVE: To assess the relative importance of soluble (Sol) and membrane-bound (M-B) components of aminopeptidase (AP) activities in local functions of male and female gonads. DESIGN: Observational study. SETTING: University research. ANIMAL(S): Adult male and female Sprague-Dawley rats in the proestrous phase of the estrous cycle. INTERVENTION(S): Samples from the right testis and the whole right ovary were dissected after perfusion with saline. The Sol and M-B fractions were obtained from these samples. MAIN OUTCOME MEASURE(S): Fluorometric measurement of Sol and M-B AP activities using arylamide derivatives as substrates. RESULT(S): Highly significant differences between male and female gonads were observed. Sol AP activities showed a significant predominance in testes, whereas M-B AP activities were significantly higher in ovaries. CONCLUSION(S): There was a discrepancy in the distribution of Sol and M-B AP activities between male and female gonads, which may imply a direct participation of sex steroids in AP activities. These results may reflect the relative importance of these enzymes in the testis and ovary and should be taken into account in evaluating the functional role of peptides locally produced in gonads.     

HLA-DM, HLA-DO and tapasin: functional similarities and differences.

In both the MHC class II and class I pathways of antigen presentation, accessory molecules influence formation of MHC-peptide complexes. In the MHC class II pathway, DM functions in the loading and editing of peptides; recent work demonstrated that it is acting not only in late endosomal compartments but also in recycling compartments and on the surface of B cells and immature dendritic cells. DM activity is modulated by another accessory molecule, DO, but this modulation is mainly operative in B cells, where it may lead to preferential activation of B cells producing high-affinity antibodies. In the MHC class I pathway of antigen presentation, recent in vivo experiments with knockout mice confirmed the role of tapasin in antigen presentation and indicate that it acts as a peptide editor and as a chaperone for TAP and the MHC class I heavy chain. In the class I loading complex, calreticulin and the thiol-dependent oxidoreductase ER60/ERp57 appear to support the function of tapasin in an as-yet-unknown fashion. The picture emerges that DM and tapasin have analogous functions in shaping the peptide repertoire presented by the respective MHC class II and class I molecules.     

Downmodulation of antigen presentation by H2-O in B cell lines and primary B lymphocytes

Peptide loading onto MHC class II molecules takes place in endosomal compartments along the endocytic pathway. There, loading is facilitated by the catalytic function of the accessory molecule H2-M, which helps to exchange the invariant chain-derived CLIP peptide in the groove of class II molecules for antigenic peptide. H2-O is another accessory molecule specific to the class II pathway, which is found tightly associated with H2-M and selectively expressed in B cells. Using stable H2-O ribozyme-antisense transfectants, H2-O overexpressing murine B cell lines, and H2-O-transgenic mice, we investigated the effects of H2-O on antigen presentation. The results show that presentation of a variety of exogenous protein antigens to a panel of T cell hybridomas depended on the levels of H2-O in the antigen-presenting B cells. Thus, increased H2-O expression downmodulated, whereas reduced H2-O levels, enhanced presentation. Presentation of endogenous antigen was also diminished by H2-O. Despite the pronounced effects on antigen presentation, the mass spectrometric profiles of peptides eluted from Ab molecules were very similar in cells expressing different H2-O levels. The intracellular location of H2-O inhibitory activity was investigated with the drug chloroquine, which prevents acidification of the endocytic pathway. The observations indicate that H2-O predominantly inhibits antigen presentation in early endosomal compartments. Thus, H2-O appears to skew peptide loading to late endosomal/lysosomal compartments. This may favor presentation of antigens taken up by the B cell receptor.     

Impaired immune responses and altered peptide repertoire in tapasin-deficient mice

Tapasin is a component of the major histocompatibility complex (MHC) class I antigen-loading complex. Here we show that mice with a disrupted tapasin gene display reduced MHC class I expression. Cytotoxic T cell (CTL) responses to viruses are impaired, and dendritic cells of tapasin-deficient mice do not cross-present protein antigen via the MHC class I pathway, indicating a defect in antigen processing. Natural killer (NK) cells from tapasin-deficient mice have an altered repertoire and are self-tolerant. In addition, the repertoire of class I-bound peptides is altered towards less stably binding ones. Thus tapasin plays a role in CTL and NK immune responses and in optimal peptide selection.