title: Exogenous cysteine and cystine promote cell proliferation in CaCo-2 cells.
abstract: Previous studies have shown that intracellular glutathione, a ubiquitous intracellular thiol, is related to cell proliferation and that cysteine or its disulphide form, cystine, also induces cell proliferation. Cysteine is a thiol containing amino acid and a rate-limiting precursor of glutathione. Therefore, it is still unresolved as to whether the proliferative effect of cysteine or cystine is entirely mediated by a change in the intracellular glutathione status. The objective of this study was to delineate the relationship among cysteine/cystine (thereafter referred to as cyst(e)ine), intracellular glutathione and cell proliferation in the human colon cancer CaCo-2 cell line. CaCo-2 cells were cultured in cyst(e)ine-free Dulbecco's Modified Eagle Medium without serum, and treated with 200 microm cysteine and/or 200-400 microm cystine for 24 h. In the presence of DL-buthionine-[S, R]-sulfoximine (BSO), a glutathione synthesis inhibitor, exogenously administered cyst(e)ine did not change the intracellular glutathione content, but increased the intracellular cysteine as well as cystine level. Addition of exogenous cyst(e)ine following 5 mm BSO treatment significantly increased cell proliferation as measured by 3H-thymidine incorporation and protein content. Cell cycle analyses revealed that cyst(e)ine promoted cell progression from the G1 phase to the S phase. Correspondingly, cyst(e)ine treatment induced expression of cyclin D1 and phosphorylation of retinoblastoma protein (Rb). In conclusion, these data indicate that both cysteine and cystine have proliferative effects in CaCo-2 cells independent of an increase in intracellular glutathione. Induction of cyclin D1, phosphorylation of Rb, and subsequent facilitation of G1-to-S phase transition were involved in the proliferative effect of exogenous cyst(e)ine.
authors.affiliation: Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, LA 71130-3932, USA.
authors.forename: T
authors.initials: T
authors.lastname: Noda
authors.forename: R
authors.initials: R
authors.lastname: Iwakiri
authors.forename: K
authors.initials: K
authors.lastname: Fujimoto
authors.forename: C A
authors.initials: CA
authors.lastname: Rhoads
authors.forename: T Y
authors.initials: TY
authors.lastname: Aw
mesh_terms: D000963:Antimetabolites / Q000494:pharmacology; D015153:Blotting, Western; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D018938:Caco-2 Cells; D002851:Chromatography, High Pressure Liquid; D019938:Cyclin D1 / Q000378:metabolism; D003545:Cysteine / Q000032:analysis / Q000494:pharmacology*; D003553:Cystine / Q000032:analysis / Q000494:pharmacology*; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects*; D005978:Glutathione / Q000032:analysis / Q000096:biosynthesis; D019803:Glutathione Disulfide / Q000032:analysis / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase / Q000187:drug effects*
chemical_list: D000963:Antimetabolites; D016160:Retinoblastoma Protein; D019938:Cyclin D1; D003553:Cystine; D019328:Buthionine Sulfoximine; D005978:Glutathione; D003545:Cysteine; D019803:Glutathione Disulfide