This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fiskerstrand, T. Articles by Refsum, H. Search for Related Content PubMed PubMed Citation Articles by Fiskerstrand, T. Articles by Refsum, H.

Development and Reversion of Methionine Dependence in a Human Glioma Cell Line: Relation to Homocysteine Remethylation and Cobalamin Status¹

Department of Clinical Biology, Division of Pharmacology [T. F., B. C., P. M. U., H. R.] and Department of Pathology [O. B. T.], University of Bergen, N-5021 Haukeland Hospital, Norway

We investigated the biochemical changes which accompanied the development and reversion of methionine dependence in a human glioma cell line GaMg. This cell line attained a higher proliferation rate and more malignant morphology with increasing passages in vitro. Early passages (P10, P25, and P45) were able to grow in a methionine-deficient medium supplemented with homocysteine (Met^-Hcy⁺), while a later passage (P60) had lost this ability, i.e., it had become methionine-dependent. From P60 cells, a methionine-independent revertant (P60R) was established by exposing the cells to 5-aza-2-deoxycytidine, followed by culture in a Met^-Hcy⁺ medium. In these genetically related cell lines, we investigated homocysteine remethylation and the functional state of cobalamin-dependent methionine synthase, the enzyme responsible for remethylation of homocysteine to methionine. The methionine synthase activity in cell extracts was similar in all cell sublines. Intact cell methionine biosynthesis and nitrous oxide-dependent homocysteine export reflect homocysteine remethylation in cells cultured in a Met^-Hcy⁺ and methionine-containing (Met⁺Hcy^-) medium, respectively. Both of these parameters, as well as the cellular content of the substrate 5-methyltetrahydrofolate, and the cofactor methylcobalamin, in addition to adenosylcobalamin, were high in P10, declined progressively in P45 and P60, and were restored in P60R. P25 cells had some unique features among the methionine-independent phenotypes because both homocysteine remethylation and the level of 5-methyltetrahydrofolate were low in Met⁺Hcy^- medium. The maximal homocysteine export rate in the presence of nitrous oxide, which reflects the overall transmethylation rate, was high in P60 and even higher in P60R compared to the lower passages. The basis for development of methionine dependence during culture of this glioma cell line seems related to the combined effects of reduced methionine biosynthesis and an increased overall transmethylation rate. The single parameter which most closely correlated to the ability to use homocysteine for growth was methylcobalamin. These data support a model for methionine dependence, which implies impaired provision of cobalamin to methionine synthase.

¹ This work was supported by grants from the Norwegian Cancer Society and the Norwegian Research Council.

² To whom requests for reprints should be addressed, at Department of Clinical Biology, Division of Pharmacology, University of Bergen, Armauer Hansens hus, 5021 Bergen, Norway.

Received 5/ 9/94. Accepted 8/ 4/94.

This article has been cited by other articles:

				D. E. Epner Can Dietary Methionine Restriction Increase the Effectiveness of Chemotherapy in Treatment of Advanced Cancer? J. Am. Coll. Nutr., October 1, 2001; 20(90005): 443S - 449. [Abstract] [Full Text]

				B. Tang, Y. N. Li, and W. D. Kruger Defects in Methylthioadenosine Phosphorylase Are Associated with but not Responsible for Methionine-dependent Tumor Cell Growth Cancer Res., October 1, 2000; 60(19): 5543 - 5547. [Abstract] [Full Text]

				T. Fiskerstrand, B. Riedel, P. M. Ueland, B. Seetharam, E. H. Pezacka, S. Gulati, S. Bose, R. Banerjee, R. K. Berge, and H. Refsum Disruption of a Regulatory System Involving Cobalamin Distribution and Function in a Methionine-dependent Human Glioma Cell Line J. Biol. Chem., August 7, 1998; 273(32): 20180 - 20184. [Abstract] [Full Text] [PDF]

				T. Fiskerstrand, P. M. Uel, and a. H. Refsum Folate Depletion Induced by Methotrexate Affects Methionine Synthase Activity and Its Susceptibility to Inactivation by Nitrous Oxide J. Pharmacol. Exp. Ther., September 1, 1997; 282(3): 1305 - 1311. [Abstract] [Full Text]

				S. Gulati, Z. Chen, L. C. Brody, D. S. Rosenblatt, and R. Banerjee Defects in Auxiliary Redox Proteins Lead to Functional Methionine Synthase Deficiency J. Biol. Chem., August 1, 1997; 272(31): 19171 - 19175. [Abstract] [Full Text] [PDF]

				H. Jakubowski and H. Jakubowski Metabolism of Homocysteine Thiolactone in Human Cell Cultures. POSSIBLE MECHANISM FOR PATHOLOGICAL CONSEQUENCES OF ELEVATED HOMOCYSTEINE LEVELS J. Biol. Chem., January 17, 1997; 272(3): 1935 - 1942. [Abstract] [Full Text] [PDF]