THE INDUCTION OF APOPTOSIS IN HUMAN CERVICAL-CARCINOMA (HELA) CELLS BY GAMMA-LINOLENIC ACID

A high concentration (50 mu g/ml) of gamma-linolenic acid (GLA) induce d morphological lesions typical of apoptosis, as well as DNA fragmenta tion, in HeLa cells. A lower concentration of GLA (20 mu g/ml), caused an increased proliferating cell nuclear antigen (PCNA) labelling, wit h 92.7% cells positive, compared to 27.7% at a concentration of 50 mu g/ml GLA. In correlation with these results, the number of cells with degraded DNA below the G(0)/G(1) peak increased significantly in the 5 0 mu g/ml GLA-treated cells, but increased only slightly in cells expo sed to the lower level of GLA. The high levels of PCNA induced by 20 m u g/ml GLA, in both G(1) and S phases, may indicate a state of DNA rep air synthesis, whilst at the higher concentration of GLA, most of the cells became apoptotic. Since apoptosis is associated with the deregul ation of c-Myc expression, and as the Raf-1-MAP kinase cascade activat es the expression of c-Myc and c-Jun, we investigated the effects of 2 0 and 50 mu g/ml GLA on the Raf-1, c-Myc and c-Jun levels, and on the activity of MAP kinase. The results showed that 50 mu g/ml GLA lowered the activity of MAP kinase. As expected with the decreased MAP kinase activity in the cells exposed to the higher level GLA, the c-Jun leve ls were also lowered. The levels of c-Myc, however, were increased. it is therefore possible that the deregulated expression of c-Myc in the HeLa cells exposed to the high level of GLA (50 mu g/ml) may contribu te to the induction of apoptosis in HeLa cells.