title: Fish oil slows S phase progression and may cause upstream shift of DHFR replication origin ori-beta in CHO cells.
abstract: Fish oils (FOs) have been noted to reduce growth and proliferation of certain tumor cells, effects usually attributed to the content of polyunsaturated fatty acids of the n-3 family, which are thought to modulate cellular signaling pathways. We investigated the influence of FO on cell cycle kinetics of cultured Chinese hamster ovary cells. Exponentially growing cells were labeled with 5-bromo-2'-deoxyuridine (BrdU) and analyzed by flow cytometry after 5-day treatment with exogenous fat. Bivariate BrdU-DNA analysis indicated slower progression through S phase and thus longer S phase duration time in FO- but not corn oil-treated or control cells. We hypothesize that FO treatment might interfere with spatial/temporal organization of replication origins. Therefore, we mapped the well-characterized replication origin ori-beta downstream of the dihydrofolate reductase gene with the nascent strand length assay. Three DNA marker segments with known positions relative to this origin were amplified by PCR. By quantitatively assessing DNA length of the fragments in all fractions containing these markers, the location of ori-beta was established. In control or corn oil-treated cells, the location of ori-beta was consistent with previous studies. However, in FO-treated cells, DNA replication appears to start from a new site located farther upstream from ori-beta, suggesting a different replication initiation pattern. This study suggests novel mechanism(s) by which fats affect cell proliferation and DNA replication in mammalian cells.
authors.affiliation: Section of Endocrinology, Diabetes, and Nutrition, Department of Medicine, Boston University School of Medicine, 88 E Newton Street, Evans 201, Boston, MA 02118, USA. nsteph3@cs.com
authors.forename: Nawfal W
authors.initials: NW
authors.lastname: Istfan
authors.forename: Zhi-Yi
authors.initials: ZY
authors.lastname: Chen
authors.forename: Sybille
authors.initials: S
authors.lastname: Rex
mesh_terms: D000818:Animals; D001973:Bromodeoxyuridine / Q000493:pharmacokinetics; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D003314:Corn Oil / Q000494:pharmacology; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects*; D005260:Female; D005395:Fish Oils / Q000494:pharmacology*; D005434:Flow Cytometry; D010053:Ovary / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018741:Replication Origin / Q000187:drug effects*; D016196:S Phase / Q000187:drug effects* / Q000502:physiology; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D005395:Fish Oils; D003314:Corn Oil; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase; D001973:Bromodeoxyuridine