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B Rossi

Publications and source records attributed to B Rossi.

At least 19 recordsLinked to original sources
PubMed1992

N-linked oligosaccharide chains of the insulin receptor beta subunit are essential for transmembrane signaling.

Insulin receptor (IR) is a glycoprotein possessing N-linked oligosaccharide side chains on both alpha and beta subunits. The present study focuses for the first time on the potential contribution of N-linked oligosaccharides of the beta subunit in the processing, structure, and function of the insulin receptor. To investigate this point, a receptor mutant (IR beta N1234) was obtained by stable transfection into Chinese hamster ovary cells of an IR cDNA modified by site-directed mutagenesis on the four potential N-glycosylation sites (Asn-X-Ser/Thr) of the beta subunit. The mutated receptor presents an alpha subunit of 135 kDa, indistinguishable from the wild type alpha subunit, but the beta subunit has a reduced molecular mass (80 kDa instead of 95 kDa) most likely due to the absence of N-glycosylation. Metabolic labeling experiments indicate a normal processing and maturation of this mutated receptor which is normally expressed at the surface of the cells as demonstrated by indirect immunofluorescence. The affinity of the mutant for insulin (Kd = 0.12 nM) is similar to that of the wild type receptor (Kd = 0.12 nM). However, a major defect of the mutated IR tyrosine kinase was assessed both in vitro and in vivo by (i) the absence of insulin-stimulated phosphorylation of the poly(Glu-Tyr) substrate in vitro; (ii) the reduction of the insulin maximal stimulation of the mutated IR autophosphorylation in vitro (2-fold stimulation for the mutant receptor as compared to a 7-fold stimulation for the wild type); and (iii) a more complex alteration of the mutated receptor tyrosine autophosphorylation in vivo (3-fold increase of the basal phosphorylation and a 4-fold simulation of this phosphorylation as compared to the wild type receptor, the phosphorylation of which is stimulated 14-fold by insulin). The physiological consequences of this defect were tested on three classical insulin cellular actions; in Chinese hamster ovary IR beta N1234, glucose transport, glycogen synthesis, and DNA synthesis were all unable to be stimulated by insulin indicating the absence of insulin transduction through this mutated receptor. These data provide the first direct evidence for a critical role of oligosaccharide side chains of the beta subunit in the molecular events responsible for the IR enzymatic activation and signal transduction.

Amino Acid Sequence↗
PubMed1992

Characterization and purification of a guanidinobenzoatase: a possible marker of human renal carcinoma.

Guanidinobenzoatases are cell surface-associated proteinases supposed to be involved in cancer metastasis, cell migration, and tissue remodeling. The main features of the guanidinobenzoatase associated with human renal carcinoma plasma membrane are weak membrane association, continuous cleavage of p-nitrophenyl-p'-guanidinobenzoate conversely to the site titration effect of this compound when used with trypsin, and a peculiar sensitivity to serine protease inhibitors, compatible with a poorly active form. Plasma membrane preparation followed by agmatine-trisacryl affinity chromatography allows the purification of guanidinobenzoatase to homogeneity with an apparent enrichment factor of 450. Purified guanidinobenzoatase appears as a single polypeptide chain of M(r) 80,000, likely stabilized by intrachain disulfides bonds. The properties of purified guanidinobenzoatase indicate that it is an original enzyme in spite of some similarities with plasminogen activators. Indeed, in addition to differences in substrate and inhibitor specificity, guanidinobenzoatase is not recognized by specific monoclonal antibodies directed against plasminogen activators or their single-chain precursors. Thus, human renal carcinoma guanidinobenzoatase appears to be an original enzyme whose activity is undetectable in the nontumoral tissue of origin. In this respect, use of purified guanidinobenzoatase would allow us to obtain specific tools to give new insights in cancer cell metastasis.

Adenocarcinoma↗
PubMed1992

Jurkat T cells express a functional neutral endopeptidase activity (CALLA) involved in T cell activation.

We have characterized a T lymphocyte endopeptidase activity that hydrolyses succinyl-alanine-alanine-phenylalanine-paranitroanilide (Suc-Ala-Ala-Phe-pNa). Hydrolysis of this substrate by intact Jurkat T cells was markedly enhanced when exogenous aminopeptidase N was added to the incubation medium. It thus appears that the release of paranitroaniline from Suc-Ala-Ala-Phe-pNA results from the combination of two distinct enzymatic activities: (i) an endopeptidase activity that cleaves the substrate at the alanyl bond and (ii) an aminopeptidase activity that ultimately cleaves the phenylalanyl bond. This cleavage was further confirmed by HPLC analysis. Specific endopeptidase 24.11 inhibitors were shown to inhibit the endopeptidase activity. These features are reminiscent of the characteristics of neutral endopeptidase (NEP, also known as endopeptidase 24.11, CALLA or CD10). Anti-CD10 monoclonal antibodies (mAbs) recognized the CD10+ B cell line Raji, but not Jurkat cells as assessed by FACS analysis. This is probably due to a lack of sensitivity of this method, the level of NEP activity in Jurkat T cells being 3-5% of that measured in B cell lines. Anti-CD10 mAbs immunoprecipitated endopeptidase 24.11 activities in both Jurkat T cells and Raji B cells, demonstrating that T lymphocytes express a CALLA-related endopeptidase. We also demonstrate that T and B cell endopeptidases have the same molecular weight, that T cells express less functional CALLA mRNA than B cells and that there are at least two shorter transcripts (1.8 and 0.8 kb) in both T and B cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Ocular myopathy without ophthalmoplegia can be a form of mitochondrial myopathy.

To characterize muscle pathology in 3 cases affected by ocular myopathy with eyelid ptosis and upper facial weakness, but without ophthalmoplegia, light microscopy and ultrastructural study were performed on levator palpebrae, orbicularis oculi and deltoid muscle biopsies. While levator palpebrae proved uninformative because of the massive fibrous degeneration of muscle, orbicularis oculi biopsies showed histochemical and ultrastructural alterations indicating a mitochondrial involvement, resembling that reported in ocular mitochondrial myopathies (OMM). On the other hand very mild aspecific findings were observed in deltoid. We suggest that these cases with ocular myopathy and without ophthalmoplegia should be considered a partial or initial form of OMM.

Adult↗
PubMed1992

Variability of the expression of muscle mitochondrial damage in ocular mitochondrial myopathy.

In this study we comparatively analysed deltoid histochemistry, biochemistry and mitochondrial DNA (mtDNA) in two groups of ten sporadic ocular mitochondrial myopathies (OMM), respectively with and without ragged red fibres (RRF). (1) All but one RRF--patients presented the mild form of OMM with blepharoptosis but without ophthalmoplegia; (2) the occurrence of cytochrome c oxidase deficient (COX-) fibres was significantly higher in the RRF+ group, but four RRF- cases also showed COX- fibres; (3) no difference was observed in biochemical findings between the groups; (4) two RRF- patients without COX- fibres showed mtDNA heteroplasmy; (5) in two RRF- patients without deltoid mtDNA deletion, biopsy of an eyelid muscle showed significant mitochondrial alterations. These results suggest that the expression of a mitochondrial defect can vary and that the absence of RRF in a skeletal muscle biopsy does not necessarily rule out the diagnosis of OMM, if other data support that.

Adolescent↗
PubMed1992

Clinical and electrophysiological reports in a case of early onset myotonia congenita (Thomsen's disease) successfully treated with mexiletine.

A sporadic event of myotonia congenita in a infant admitted to the Paediatric Clinic for frequent crises of apnoea, cyanosis, vomiting and difficult feeding is reported. EMG analysis was consistent with the dominant variety of myotonia congenita. Mexiletine therapy showed excellent results in reducing myotonic activity. It is worthwhile stressing that early symptoms may go unnoticed or may be misinterpreted and that information on the genetic form of the disease can be obtained also from the EMG analysis through a repetitive stimulation test.

Electromyography↗
PubMed1992

Peripheral neuropathy in mixed cryoglobulinemia: clinical and electrophysiologic investigations.

Peripheral neuropathy has been described in different rheumatic diseases such as rheumatoid arthritis, systemic lupus erythematosus and systemic vasculitis, but usually in limited numbers of patients. Nerve injury is more frequently reported in mixed cryoglobulinemia. In earlier studies generally performed in small series of patients, prevalence of peripheral neuropathy varied widely. We evaluated prevalence of peripheral neuropathy in 33 unselected patients with mixed cryoglobulinemia (25 women, 8 men, aged from 45-71 years). Neurologic involvement was detected using a complete clinical and electrophysiologic assessment, including sensory motor conduction velocities, F wave and H reflex. Neurologic examination revealed a neuropathy in 48% of subjects, while electrophysiologic variables were altered in 82%; a percentage similar to that of subjective symptoms (91%). Among electrophysiologic investigations, F wave was altered in 22/33 subjects (67%); therefore, this variable seems to be the most reliable for the detection of neurologic involvement. Cryocrit levels were significantly higher in patients with peripheral neuropathy: abnormal examination (p less than 0.01), sensory motor conduction (p less than 0.04), and F wave alterations (p less than 0.008). In addition, hemorheological abnormalities seem to contribute to the pathogenesis of nerve injury. Our results indicate that peripheral neuropathy, to a variable degree, is present in the majority of patients with mixed cryoglobulinemia, and a complete clinical and electrophysiologic investigation can be useful for an early and correct diagnosis.

Aged↗
PubMed1979

[Personal clinical and neurophysiological experience in the surgically treated carpal tunnel syndrome].

In 18 cases of carpal tunnel syndrome treated by surgical decompression of the median nerve, a neurophysiological control was performed before and after surgery. In all cases improvement or disappearance of the pain was observed; improvement in motor function was less constant. Control of the median nerve conduction showed that in all cases with preoperative distal latency less than 6 msec. there was a normalization of the nerve conduction after only 3 months. In cases of distal latency over 6 msec, and especially in those with complete motor conduction block, the latency remain within patological limits even 15 months after surgery. This may be explained either by a slower conduction of the regenerated fibres or by a persistent myelinic and axonal damage of the nerve.

Adult↗
PubMed1979

Blink reflexes in posterior fossa lesions.

Blink reflexes obtained by electrical stimulation of the supraorbital nerve and electromyographic recording of the orbicularis oculi muscle proved useful as a preliminary method in diagnosis of lesions of the brainstem and the fifth and seventh cranial nerves, and in differentiating intrinsic lesions of the brainstem from extrinsic ones. It was noted that R1 and R2 reflexes were different in the two types of lesions.

Adolescent↗
PubMed1979

Blink reflexes in severe traumatic coma.

Blink reflexes were studied in 21 patients in coma after severe head injury. Our observations suggest that blink reflexes are a simple, objective, neurophysiological test to evaluate brainstem function. Correlations between these reflexes and the anatomoclinical stanges of coma and the Glasgow coma scale have been established. Presence of the early R1 component shows the integrity of at least a part of the pontine structures. The appearance of the late R2 component is correlated with a better chance of recovery from coma.

Acute Disease↗
PubMed1979

Body perception in athletes and non-athletes.

20 male athletes and 20 control subjects were required to make estimates of the length of their body dimensions and of external comparison objects. Athletes were more accurate in judging body dimensions than comparison objects while the reverse pattern was demonstrated by non-athletes. The results are discussed on the basis of the possible influence of sports activities on body perception.

Adolescent↗
PubMed1977

[Muscular malformation of the wrist in an initial carpal tunnel syndrome. Clinical case].

A carpal canal syndrome in a young female subject was found at the operating table to be due to a wrist muscle abnormality. An extra muscle leaving the styloid process of the radius in the direction of the transverse ligament of the carpus, and an abnormal distal development of the muscular belly of the superficial flexor of the third finger, had led to compression on the median nerve corresponding to the carpal canal. Check on motor and sensitive conduction of the median nerve revealed nerve damage at wrist level. Removal of the extra muscle and section of the transverse ligament of the carpus resolved the painful symptomatology. Control of nervous conduction two months after operation confirmed the improvement.

Adult↗
PubMed1976

(Na+, K+)-activated adenosinetriphosphatase of axonal membranes, cooperativity and control. Steady-state analysis.

1. The ATP sites. Homotropic interactions between ATP sites have been studied in a very large range of Na+ and K+ concentrations. The ( Na+, K+)-activated ATPase displays Michaelis-Menten kinetics for ATP under standard concentration conditions of Na+ (100 mM) and K+ (10 mM). The steady-state kinetics behavior changes at very low concentrations of K+ where negative cooperativity is observed. The existence of a high affinity and a low affinity site for ATP was clearly demonstrated from the study of the ATP stimulated hydrolysis of p-nitrophenylphosphate in the presence of Na+ and K+. The ratio of apparent affinities of high and low affinity sites for ATP is 86 at pH 7.5. 2. The Na+ sites. The binding of Na+ to its specific stimulatory sites (internal sites) is characterized by positive cooperativity with a Hill coefficient n(H(Na+))=2.0. Homotropic interactions between Na+ sites are unaffected by variations of the K+ concentration. 3. The K+ sites. (a) Binding of K+ to the (external) stimulatory site of the ATPase has been analyzed by following the (Na+, K+)-ATPase activity as well as the p-nitrophenylphosphatase activity in the presence of Na+ and K+ (with or without ATP). Binding is characterized by a Hill coefficient of 1.0 and a K(0.5(K+))=0.1 to 0.8 mM. The absence of positive or negative cooperativity persists between 5 mM and 100 mM Na+. (b) The analysis of the p-nitrophenylphosphatase or of the 2, 4 dinitrophenylphosphatase activity in the presence of K+ alone indicates the existence of low affinity sites for K+ with positive homotropic interactions. The characteristics of stimulation in that case are, K(0.5)=5 mM, n(H)=1.9. The properties of this family of site(s) are the following: firstly, saturation of the low affinity site(s) by K+ prevents ATP binding to its high affinity internal site. Secondly, saturation of the low affinity sites for K+ prevents binding of Na+ to its internal sites. Thirdly, this family of sites disappears in the presence of ATP, p-nitrophenylphosphate or of both substrates, when Na+ binds to its internal sites. Na+ binding to its specific stimulatory sites provokes the formation of the high affinity type of site for K+. 4. Mg2+ stimulation of the (Na+, K+)-ATPase is characterized by a Hill coefficient n(H(Mg2+))=1.0 and a K(0.5(Mg2+))=1 mM stimulation is essentially a V effect. Heterotropic effects between binding of Mg2+ and substrate to their respective sites are small. Heterotropic interactions between the Ms2+, Na+ and K+ sites are also small. 5. The fluidity of membrane lipids also controls the (Na+, K+)-ATPase activity. Phase transitions or separations in the membrane hardly affect recognition properties of substrates, Na+, K+ and Mg2+ for their respective sites on both sides of the membrane. Only the rate of the catalytic transformation is affected.

Acetylcholinesterase↗
PubMed1976

[Familial myotonic syndrome with hyposthenia corrected with exercise (author's transl)].

In some cases of myotonic syndromes a paresis after rest has been described corrected by exercise. This syndrome is reported in two brothers. In myotonic patients repetitive stimulation of a nerve causes a transitory decrease of the muscle action potential. Probably the paresis corrected by exercise only represents the clinical evidence of the electrophysiological phenomenon mentioned above. This seems to be a common occurrence and therefore does not represent a new nosologic entity.

Adult↗