The cell cycle dependence of c-sis gene expression: artifactual conclusions in cells prepared by chemical but not physical techniques.

The c-sis oncogene encoding the B-chain of platelet-derived growth factor (PDGF) may be involved in an autocrine growth stimulation of tumours expressing the PDGF receptor, such as glioblastomas and sarcomas. To investigate whether expression of c-sis RNA is regulated in a cell cycle dependent manner, human A172 glioblastoma cells were synchronized by either centrifugal elutriation or chemical blockage with the DNA synthesis inhibitors hydroxyurea or aphidicolin. In non-perturbed elutriated cells, c-sis RNA levels were lower in the S phase of the cell cycle than in the G1 phase. In contrast, the chemically synchronized cells revealed a transient rise in c-sis RNA shortly after drug release, in early S phase. The RNA changes occurring after release from drug inhibition represent cell recovery from drug induced metabolic disturbances rather than true cell cycle dependent effects.