Regulation of glutamine synthetase in human breast carcinoma cells and experimental tumors.
BACKGROUND
Acute deprivation of extracellular glutamine causes up-regulation of glutamine synthetase (GS) expression by a mechanism involving an increase in GS protein stability. This study examines GS expression in a highly glutamine-dependent and tumorigenic human breast cancer cell line, TSE cells, in response to acute and chronic glutamine deprivation in culture and during tumor formation.


METHODS
TSE cells were subjected to acute glutamine deprivation, adapted to growth in low glutamine concentrations, and subcutaneously injected into nude mice. GS protein and mRNA levels were assayed by Western and Northern blotting, and intracellular glutamine levels were evaluated by using a colorimetric assay.


RESULTS
GS protein levels increased, but GS mRNA levels were unchanged in response to acute glutamine deprivation. Chronic glutamine deprivation in vitro and tumor growth in vivo caused an increase in both GS protein and mRNA levels. Large tumors exhibited lower intracellular glutamine, higher GS protein, and relatively unchanged GS mRNA levels relative to small tumors.


CONCLUSIONS
TSE tumors exhibit up-regulation of GS protein and mRNA levels and declines in intracellular glutamine content, suggesting that growth in vivo causes a chronic and progressive glutamine deprivation. Up-regulation of GS expression may contribute to adaptation to a nutrient-poor intratumor environment.
Collins
C L
CL
Department of Surgery, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA.
Wasa
M
M
Souba
W W
WW
Abcouwer
S F
SF
D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D005974:Glutamate-Ammonia Ligase / Q000096:biosynthesis*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D012333:RNA, Messenger; D005973:Glutamine; D018698:Glutamic Acid; D005974:Glutamate-Ammonia Ligase