Specific increase in thymidine transport at a permissive temperature in the rat kidney cells infected with srcts-Rous sarcoma virus

Tyrosine-phosphorylated caveolin-1: immunolocalization and molecular characterization

Caveolin-1 was discovered as a major substrate for v-Src, but the effect of its tyrosine phosphorylation has not been known. We generated a specific antibody (PY14) to caveolin-1 phosphorylated at tyrosine 14 and studied the significance of the modification. By Western blotting of lysates of v-Src-expressing cells, PY14 recognized not only a 22-kDa band (the position of nonphosphorylated caveolin-1) but bands at 23-24 and 25 kDa. Bands of slower mobility were diminished by dephosphorylation and were also observed for mutant caveolin-1 lacking tyrosine 14. By immunofluorescence microscopy, PY14 did not label normal cells but detected large dots in v-Src-expressing cells. Immunoelectron microscopy revealed that the dots corresponded to aggregated caveolae and/or vesicles of various sizes; besides, the label was observed in intramembrane particle-free areas in the plasma membrane, which appeared to have been formed by fusion of flattened caveolae. A positive reaction with PY14 was found in normal cells after vanadate or pervanadate treatment; it occurred mainly at 22 kDa by Western blotting and was not seen as large dots by immunofluorescence microscopy. Detergent solubility, oligomerization, and association with caveolin-2 were observed similarly for caveolin-1 in normal and v-Src-expressing cells. The results indicate that phosphorylation of caveolin-1 in v-Src-expressing cells occurs at multiple residues and induces flattening, aggregation, and fusion of caveolae and/or caveolae-derived vesicles.

A unifying model of the cell proliferation emphasizing plasma membrane fluxes

The regulation of cellular growth and proliferation is perhaps the most investigated and elusive problem in cell biology and seems to be possible to solve from almost any angle of study chosen. Among the non-systemic factors that have been discussed are genetic damage, genomic control, regulation by stimulatory and inhibitory peptide factors such as EGF, chalones, and fibronectin, protein kinase activation with tyrosine phosphorylation, adenylylcyclase and cAMP, cGMP, membrane perturbations and specifically in tumours the failure of the Pasteur effect in control of glycolysis, excessive membrane ATPase activity, and excessive hydrolytic and proteolytic activities at the cell surface. This article focuses on the central role of fluxes within the plasma membrane and re-examines the possibility that changes of flux of metabolites, ions, and reducing equivalents may be the common denominator regulating cellular proliferation.

Differential sensitivity of RSVts (temperature-sensitive Rous-sarcoma virus)-infected rat kidney cells to nucleoside antibiotics at permissive and non-permissive temperatures

Among a variety of anti-tumour agents tested, oxanosine and 5-azacytidine were found to be significantly more effective in inhibiting growth of rat kidney cells infected with a temperature-sensitive mutant of Rous sarcoma virus at a permissive temperature (33 degrees C) than at a non-permissive temperature (39 degrees C). These two nucleoside antibiotics were antagonistic to each other in cytotoxicity. They seem to share the same carrier-mediated membrane-transport system, because dipyridamole, a potent inhibitor of nucleoside transport, protected cells from the cytotoxicity of both drugs. Thymidine transport, which is twice as fast in cells at 33 degrees C as at 39 degrees C, was competitively inhibited by both drugs. Thus the differential toxicity of oxanosine and 5-azacytidine at the two temperatures is thought to be due to their increased transport via the thymidine-transport system, which is somehow under the influence of the active src-gene product.