Inhibition of DNA replication by fish oil-treated cytoplasm is counteracted by fish oil-treated nuclear extract

We have recentlynoted that cells treated with fish oil and n-3-fatty acids showslower DNA replication rates than cells treated with a control emulsionor corn oil only. However, it is not clearly understood howsuch an effect is induced. Fish oil and its metabolites are known tohave several modulating effects on signal transduction pathways.Alternatively, they may influence DNA replication by interactingdirectly with nuclear components. To investigate this problem ingreater detail, we have studied the kinetics of DNA synthesis in acell-free system derived from HeLa cells. Nuclei and cytosolic extractwere isolated from cells synchronized in early S phase after treatmentwith control emulsion, corn oil, or fish oil, respectively. The nucleiwere reconstituted with cytosolic extract and a reaction mixturecontaining bromodeoxyuridine (BrdU) triphosphate to label newlysynthesized DNA. The rate of DNA synthesis was measured by bivariateDNA/BrdU analysis and flow cytometry. We show that fish oil-treatedcytosol inhibits the elongation of newly synthesized DNA by ~80% incontrol nuclei. However, nuclei treated with fish oil escape thisinhibitory effect. We also show that addition of nuclear extract fromfish oil-treated cells reverses the inhibitory effect seen in thereconstitution system of control nuclei and fish oil-treated cytosol.These results indicate that polyunsaturated fatty acids can modulateDNA synthesis through cytosolic as well as soluble nuclear factors.