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S Alemà

Publications and source records attributed to S Alemà.

At least 37 records · Page 2Linked to original sources
PubMed1991

Transcription of muscle-specific genes is repressed by reactivation of pp60v-src in postmitotic quail myotubes.

Quail myogenic cells infected with temperature sensitive (ts) mutants of Rous sarcoma virus (RSV) exhibit a temperature-dependent transformation and block of differentiation. When the cells are allowed to differentiate at the restrictive temperature (41 degrees C) and then shifted back to the permissive temperature (35 degrees C), a sharp reduction in the accumulation of muscle-specific mRNAs is observed, following reactivation of the transforming protein pp60v-src. A kinetic analysis of this down-regulation reveals that the reduction in the accumulation of muscle-specific transcripts occurs fairly rapidly within 6 to 20 h after the shift back, depending on the mRNA analyzed. Studies on transcription of endogenous muscle-specific genes and a transfected chloramphenicol acetyltransferase reporter gene under the control of muscle-specific promoters, at the different temperatures, suggest that the oncogene exerts its control mainly at the transcriptional level. On the contrary, transcription of the CMD1 gene, the avian homolog of the mouse muscle regulatory MyoD gene, is not significantly affected by the oncogene both in proliferating myoblasts and in myotubes shifted back to 35 degrees C. These findings are consistent with the conclusion that v-src blocks myogenesis by controlling transcription of muscle-specific genes independently of cell proliferation. Furthermore, they suggest the existence of an alternative pathway, not requiring the silencing of CMD1 transcription, through which the oncogene exerts its effect.

Actins↗
PubMed1990

Differential control of muscle-specific gene expression specified by src and myc oncogenes in myogenic cells.

Myogenic cells can be transformed in vitro by the introduction of several exogenous viral oncogenes. Transformed myoblasts are prevented from terminal differentiation into myotubes by the continuous expression of oncogenes such as myc and src, chosen as prototypes of nuclear and cytoplasmic oncogenes. A comparative analysis of the relationship between transformation and differentiation in myoblasts and cells belonging to other lineages has led to the proposal that terminal differentiation of myc-transformed quail myoblasts is indirectly prevented by the loss of growth control and that myc-bearing cells remain susceptible to growth regulation by interaction with adjacent normal cells. On the contrary, the src oncogene appears to affect expression of the myogenic programme via a direct mechanism, independent from abnormal growth control. There is increasing evidence for the existence of master regulatory genes that govern and influence muscle development in vivo and myogenic differentiation in vitro. Expression of cytoplasmic oncogenes such as src, ras and polyoma middle T in the mouse myogenic cell line, C2, results in inhibition of biochemical differentiation and a marked down-regulation of the MyoD1 and myogenin genes.

Animals↗
PubMed1990

Acetylcholine-activated currents in quail myotubes expressing viral oncogenes.

Acetylcholine-activated currents were recorded in cultured myotubes arising from embryonic quail myoblasts transformed by the v-src and v-ras oncogenes. In src-myotubes, the whole cell inward current decayed more slowly than in non-transformed controls. In ras-myotubes, the current had a faster decay and smaller amplitude than in the controls. The single-channel conductance and mean open times recorded from cell-attached patches were similar in transformed and control cells. However, in ras-myotubes the frequency of channel openings strongly decreased with time. It is concluded that oncogenic tyrosine-specific protein kinase (v-src product) and G-like p21 protein (v-ras product) can induce differential changes in the function of nicotinic ACh receptor, perhaps related to specific biochemical events elicited in the establishment of the transformed state.

Acetylcholine↗
PubMed1989

Interaction with normal cells suppresses the transformed phenotype of v-myc-transformed quail muscle cells.

We have analyzed mixed cultures of normal mammalian fibroblastic cells and transformed quail myoblasts to investigate whether the presence of an excess of normal cells could suppress the phenotype of transformed quail cells. In such mixed cultures, only v-myc-transformed cells were growth-arrested, whereas v-src-transformed myoblasts were essentially unaffected. Growth arrest appeared to reflect reversion from the transformed state, including re-expression of the myogenic differentiation program. The v-myc-transformed myoblasts were phenotypically corrected also by differentiating normal quail myoblasts, giving rise to hybrid myotubes containing nuclei from both cell types. The differential behavior of transformed cells closely paralleled the efficiency with which they established metabolic cooperation with adjacent normal cells. Our results indicate that unrestrained proliferation associated with transformation is responsible for v-myc-induced block of myogenic differentiation.

Animals↗
PubMed1985

Distinctive effects of the viral oncogenes myc, erb, fps, and src on the differentiation program of quail myogenic cells.

The relationship between susceptibility to transformation in vitro by different oncogenes and terminal differentiation was analyzed in embryonic quail myogenic cells. Infection with Rous sarcoma virus (RSV), Fujinami sarcoma virus (FSV), avian erythroblastosis virus (AEV), and the avian myelocytomatosis virus MC29 led to rapid and massive transformation. Transformed cells had distinctive morphological alterations, increased proliferation rates, and the ability to grow in agar suspension. Furthermore, homogeneously transformed cultures failed to fuse into multinucleated myotubes and to express muscle-specific genes. However, cloned populations of RSV-, FSV-, and AEV-transformed myogenic cells could, under appropriate culture conditions, partially differentiate into atypical "revertant" myotubes. In contrast, competence for terminal differentiation was completely and irreversibly suppressed on transformation by MC29. The specificity of action of a given oncogenic sequence on the inhibition of differentiation was further studied by using conditional and nonconditional transformation mutants. Myogenic cells infected with temperature-sensitive (ts) mutants of RSV and FSV exhibited a fully reversible block of differentiation after shift to restrictive temperature, while cells infected with ts34 AEV were not temperature sensitive for differentiation. Cultures infected with the partially transformation-defective mutant of MC29 td10H were morphologically transformed and acquired anchorage independence for proliferation but maintained a residual competence for terminal differentiation.

Alpharetrovirus↗
PubMed1984

Role of cell division in differentiation of myoblasts infected with a temperature-sensitive mutant of Rous sarcoma virus.

The relationship between a potential requirement for cell DNA synthesis and the expression of differentiated muscle cell functions was investigated using primary chicken embryo myoblasts infected with a temperature-sensitive mutant of Rous sarcoma virus (RSV). Under optimized conditions, transformed myoblasts growing at the permissive temperature could differentiate into multinucleated myotubes, express muscle-specific myosin, desmin and acetylcholine receptors in the absence of DNA synthesis and cell division following a shift to the non-permissive temperature. Furthermore, the experiments demonstrate that individual RSV-infected myoblasts have two options: either to divide and express the transformed phenotype or to withdraw from the cell cycle and differentiate into myotubes. The choice between these options appears to depend on the protein-kinase activity of pp60src, the src gene product.

Animals↗
PubMed1982

Characterization of alpha-latrotoxin interaction with rat brain synaptosomes and PC12 cells.

alpha-latrotoxin, a polypeptide neurotoxin purified from the venom of the spider Latrodectus mactans tredecimguttatus, induces a massive release of a variety of neurotransmitters from rat brain synaptosomes and a clonal pheochromocytoma cell line (PC12 cells). In both systems secretion of catecholamines is dose- and calcium-dependent. Efflux of catecholamines is coupled with a substantial release of intracellular ATP. Independent of alpha-latrotoxin with PC12 cells is followed by a rapid influx of calcium and sodium ions, the rate being dependent on toxin and calcium concentrations. By reductive methylation it is possible to radioactively label alpha-latrotoxin without appreciable loss of neurotoxicity. A sensitive binding assay in vitro allows the identification of a limited number of specific binding sites in central nervous system synaptic membranes and PC12 cells, for which tritiated alpha-latrotoxin displays nanomolar affinity.

Adrenal Gland Neoplasms↗
PubMed1981

Properties of end-plate channels in rats immunized against acetylcholine receptors.

1. Rats injected with purified acetylcholine receptors (AChR) extracted from electric organs of Torpedo marmorata showed clinical symptoms consistent with the development of experimental myasthenia gravis.2. Sera of rats with this disease contain high levels of anti-AChR antibodies. However, no simple correlation was found between antibody titre and miniature end-plate current (m.e.p.c.) amplitude.3. M.e.p.c.s. at the end-plates of rats injected with AChR (Anti-R), emulsified in complete Freund Adjuvant (CFA), were reduced to about one third the size of controls taken from rats injected only with CFA (Anti-CFA). Mean m.e.p.c. (Anti-R) = 0.73 +/- 0.06 nA; mean m.e.p.c. (Anti-CFA) = 2.43 +/- 0.12 nA (V(m) = -80 mV, T = 20 degrees C).4. The m.e.p.c. decay time constant, tau(m.e.p.c.), is similar at immunized and control rat end-plates. tau(m.e.p.c.) (Anti-R) = 1.32 +/- 0.06 msec; tau(m.e.p.c.) (Anti-CFA) = 1.31 +/- 0.06 msec (V(m) = -80 mV, T = 20 degrees C).5. The end-plate current decay time constant, tau(e.p.c.), is similar at immunized and control end-plates and in both cases depends exponentially on membrane potential. The change in membrane potential required to produce an e-fold change in tau(e.p.c.) is 102.0 +/- 5.72 mV at immunized (Anti-R) end-plates and 92.3 +/- 6.14 mV at control (Anti-CFA) end-plates at T = 10 degrees C.6. Acetylcholine noise was examined at immunized and control rat end-plates at 10 degrees C. Analysis of noise indicates that the single channel conductance, gamma, and mean channel life-time, tau(noise), are essentially unchanged by immunization against AChR. gamma (Anti-R) = 13.15 +/- 0.53 pS; gamma (Anti-CFA) = 12.50 +/- 0.50 pS; tau(noise) (Anti-R) = 2.9 +/- 0.18 msec; tau(noise) (Anti-CFA) = 2.68 +/- 0.14 msec (V(m) = -80 mV, T = 10 degrees C).7. Mean quantal content and Ca(2+) dependence of the end-plate potential are unchanged at immunized end-plates.8. It is concluded that at immunized end-plates the number of activated receptor-channel complexes is reduced without modification of single channel properties. In this respect the immunized rat end-plate is a good model for myasthenia gravis affected human end-plates.

Acetylcholine↗
PubMed1980

Black widow spider toxin-induced calcium fluxes and transmitter release in a neurosecretory cell line.

Several polypeptide neurotoxins affect presynaptic functions by interfering with chemical neurotransmission. This group of toxins includes botulinum toxin, tetanus toxin, beta-bungaro-toxin and black widow spider toxin (BWSTx). While the effect of the first three toxins is mainly a rapid and severe block of neurotransmitter release, BWSTx affects transmission by a massive stimulation of mediator release. Despite various hypotheses put forward to explain the action of BWSTx at the level of nerve terminals, there is still a considerable degree of uncertainty as to the cation dependence of venom action. Study of the toxin mode of action at the biochamical level has been hampered by the complexity and cellular heterogeneity of the preparations used, neuromuscular junction or synaptosomes. PC12 cell line, derived from a rat phaeochromocytoma, seems to be an excellent model in view of its property of synthesising and storing noradrenaline, dopamine and acetylcholine, and releasing them in depolarising conditions. We have recently shown that highly purified BWSTx stimulates secretion from PC12 cells of previously taken up radioactive dopamine (DA) and noradrenaline (NA) (ref. 14 and manuscript in preparation). We report here that the earliest detectable event after toxin treatment of such cells is a massive increase of cytosolic calcium.

Animals↗
PubMed1975

Interaction of different forms of haemoglobin with artificial lipid membranes.

The action of different forms of haemoglobin (oxy-, carboxy-and methaemoglobin) and myoglobin on the leakage of Rb+ out of liposomes has been investigated. The results presented will demonstrate that only methaemoglobin is particularly effective in interacting with phospholipid vesicles by changing their permeability and catalyzing a peroxidation of their unsaturated hydrocarbon chains.

Carboxyhemoglobin↗