Utilization of preformed and endogenously synthesized methionine by cells in tissue culture

Abstract

Summary Some malignant and transformed cell lines are unable to proliferate in vitro in a L-methioninedepleted medium supplemented with L-homocysteine. To investigate the utilization of preformed and endogenously synthesized methionine 4 cell lines have been chosen with a range of abilities to proliferate under such nutritional conditions. The order of the ability of these cell lines to proliferate in an L-methioninedepleted medium containing 0.1 mM L-homocysteine parallels the minimal concentration of L-methionine required for optimal growth; L-methionine auxotrophs having a greater minimal requirement. In the presence of 0.1 mM L-homocysteine all of the cell lines synthesize macromolecules from [5-14C]methyltetrahydrofolic acid during a 24h period, and the cell line with the highest methionine requirement shows the most extensive incorporation of radiolabel into DNA and RNA, both in depleted medium and in medium containing 6.7upM L-methionine. Double-label experiments using [5-14C]methyltetrahydrofolic acid and L-(methyl-3H) methionine show preferential incorporation of preformed over endogenously synthesized methionine by methionine auxotrophs. There is no alteration in the intracellular level of S-adenosyl-L-homocysteine (SAH) or SAH hydrolase activity in cells incubated for 24h in methionine-depleted medium supplemented with 0.1 mM L-homocysteine. These results suggest that certain cell lines are unable to effectively use endogenously synthesized methionine.

Agarose‐selected variants of two human tumor cell lines exhibit altered methionine auxotrophy

“…All of the agarose-selected MeWo variants exhibited a slightly higher methionine growth requirement than the parental MeWo tumor line; however, unlike the findings of Tisdale (1984), this appears to be unrelated to their ability to proliferate in methioninefree Hey+-medium or to their in vitro growth rate in methionine-containing medium.…”

Brain tumor protein synthesis and histological grades: A study by positron emission tomography (PET) with C11-L-Methionine

“…This study provides the first quantitative evidence of an hypermetabolism of protein synthesis in human gliomas. A very high exogenous uptake of essential amino-acids is an original biochemical feature of anaplastic tissues and correlates to their proliferation rate as confirmed by in vivo and in vitro studies (15,16,37). Furthermore, a metabolic alteration may be evident with PET before any CT scan signs of BBB disruption which occurs rather late in tumor development (38,39).…”

“…L. MET was proved to be one of the best substrates for the study of brain neutral amino-acid transport system (type L) at the blood-brain barrier (BBB) and neuronal membrane level (7, 8). As an essential amino-acid (9), L. MET is not synthetized or recycled in brain ceils (10,11) and its intracellular incorporation is dependant on the external supply provided by blood to the brain through the BBB (12,13,14,15,16). Transmethylation pathways, physiologically very important, involve in brain less than 1% to 2% per hour of the mass of MET taken by glial and neuronal cells (17,18,19,20).…”

Expression Profiling of Homocysteine Junction Enzymes in the NCI60 Panel of Human Cancer Cell Lines

“…In the limited number of transformed cell lines in which MS activity has been measured (33,40,41) or the coding sequence of MS has been analyzed (10), a discernable defect has not been observed. Comparable MS activity in the presence of exogenous methylcobalamin was also reported in human melanoma cell line variants, which exhibited methionine-dependent (Me-Wo-LC1) and methionine-independent (D3.12.2) phenotypes (42).…”