Early release of the density-dependent inhibition of phosphate uptake and ATP synthesis after src gene expression in chick embryo fibroblasts.

Our results showed that the expression of the src gene in chick embryo fibroblasts (CEF) released the density-dependent inhibition (DDI) of phosphate metabolism (phosphate uptake and phosphorylation of small organic compounds). With increasing cell density, phosphate metabolism decreased by 58% in normal CEF and, in contrast, increased by 20% in Rous sarcoma virus (RSV)-transformed CEF. The same change in the DDI was observed in CEF infected by NY68 (a ts mutant for transformation of RSV) and maintained at the permissive temperature (37 degrees C) instead of the restrictive temperature (41.5 degrees C) for the expression of transformation. An interesting feature was that the release of the DDI of phosphate metabolism was an early event in the process of transformation, since it was almost concomitant with the stimulation of the pp60 src kinase activity following the shift from 41.5 to 37 degrees C of NY68 CEF. The phosphorylation of small organic compounds (Po) was more strongly increased by the change in temperature than was 32Pi accumulation. Furthermore, the percentage increases of Po and adenosine triphosphate (ATP) labelling with 32P were similar, suggesting that the expression of src gene enhanced ATP synthesis. In glucose-free medium, the stimulation of Po-labelling was still observed but was decreased. Therefore the activation of glycolytic activity is not an absolute requirement, but is necessary for the maximum effect of transformation on the release of DDI of phosphate metabolism. Oligomycin added in complete medium did not prevent the increase in Po-labelling. From these results, we assumed that ATP turnover was stimulated as a consequence of enhanced ATP degradation. We verified that the stimulation of Po phosphorylation was not a consequence of increased ATP utilization for RNA or protein synthesis. The stimulation of Po labelling was specifically abolished by quercetin. This drug inhibited the transformed cells more strongly than the non-transformed cells.