Collins C L, Wasa M, Souba W W, Abcouwer S F
Department of Surgery, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA.
Surgery. 1997 Aug;122(2):451-63; discussion 463-4. doi: 10.1016/s0039-6060(97)90039-8.
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.
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.
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.
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.
细胞外谷氨酰胺的急性缺乏通过一种涉及谷氨酰胺合成酶（GS）蛋白稳定性增加的机制导致GS表达上调。本研究检测了在高度依赖谷氨酰胺且具有致瘤性的人乳腺癌细胞系TSE细胞中，培养过程中以及肿瘤形成期间急性和慢性谷氨酰胺缺乏时GS的表达情况。
使TSE细胞经历急性谷氨酰胺缺乏，适应在低谷氨酰胺浓度下生长，并皮下注射到裸鼠体内。通过蛋白质免疫印迹法和Northern印迹法检测GS蛋白和mRNA水平，使用比色法评估细胞内谷氨酰胺水平。
急性谷氨酰胺缺乏时，GS蛋白水平升高，但GS mRNA水平未改变。体外慢性谷氨酰胺缺乏和体内肿瘤生长导致GS蛋白和mRNA水平均升高。相对于小肿瘤，大肿瘤细胞内谷氨酰胺含量较低，GS蛋白水平较高，而GS mRNA水平相对不变。
TSE肿瘤表现出GS蛋白和mRNA水平上调以及细胞内谷氨酰胺含量下降，表明体内生长导致慢性进行性谷氨酰胺缺乏。GS表达上调可能有助于适应肿瘤内营养匮乏的环境。
