Bode B P, Souba W W
Division of Surgical Oncology, Massachusetts General Hospital, Harvard Medical School, Boston.
Ann Surg. 1994 Oct;220(4):411-22; discussion 422-4. doi: 10.1097/00000658-199410000-00001.
The authors determined the effects of growth inhibition on glutamine transport and metabolism in human hepatoma cells.
Hepatoma cells exhibit markedly higher (10- to 30-fold) glutamine uptake than normal human hepatocytes, via a disparate transporter protein with a higher affinity for glutamine. Currently, little is known about the effects of growth arrest on glutamine transport and metabolism in hepatoma cells.
The authors determined proliferation rates, glutamine transport, and glutaminase activities in the human hepatoma cell lines HepG2, Huh-7, and SK-Hep, both in the presence and absence of the chemotherapeutic agents novobiocin and sodium butyrate. The transport activities for alanine, arginine, and leucine also were determined in both treated and untreated cells. Glutaminase activity was determined in normal human liver tissue and compared with that present in hepatoma cells.
Glutaminase activities were similar in all three cell lines studied, despite differences in proliferation rates, and were sixfold higher than the activity in normal human liver. In contrast to normal hepatocytes, which expressed the liver-specific glutaminase, hepatomas expressed the kidney-type isoform. Sodium butyrate (1 mmol/L) and novobiocin (0.1 mmol/L) inhibited cellular proliferation and reduced both glutamine transport and glutaminase activity by more than 50% after 48 hours in the faster-growing, less differentiated SK-Hep cells. In contrast, the agents required 72 hours to attenuate glutamine uptake by 30% and 50% in the slower-growing, more differentiated HepG2 and Huh-7 cell lines, respectively. Treatment of all three cell lines with novobiocin/butyrate also resulted in a 30% to 60% attenuation of the transport of alanine, arginine, and leucine, and glutamine, indicating that inhibition of cellular proliferation similarly affects disparate amino acid transporters.
Hepatocellular transformation is characterized by a marked increase in glutamine transport and metabolism. Inhibition of cellular proliferation attenuates glutamine transport and metabolism, especially in fast-growing, relatively undifferentiated hepatoma cells. Because the uptake of other amino acids is similarly reduced under cytostatic conditions, plasma membrane amino acid transport activity in hepatoma cells is regulated by the proliferation state of the cells.
作者确定了生长抑制对人肝癌细胞中谷氨酰胺转运和代谢的影响。
肝癌细胞通过对谷氨酰胺具有更高亲和力的不同转运蛋白，表现出比正常人肝细胞明显更高（10至30倍）的谷氨酰胺摄取。目前，关于生长停滞对肝癌细胞中谷氨酰胺转运和代谢的影响知之甚少。
作者测定了人肝癌细胞系HepG2、Huh-7和SK-Hep在存在和不存在化疗药物新生霉素和丁酸钠的情况下的增殖率、谷氨酰胺转运和谷氨酰胺酶活性。还测定了处理和未处理细胞中丙氨酸、精氨酸和亮氨酸的转运活性。在正常人肝组织中测定谷氨酰胺酶活性，并与肝癌细胞中的活性进行比较。
尽管增殖率存在差异，但在所研究的所有三种细胞系中，谷氨酰胺酶活性相似，并且比正常人肝中的活性高六倍。与表达肝脏特异性谷氨酰胺酶的正常肝细胞相反，肝癌细胞表达肾型同工型。在生长较快、分化程度较低的SK-Hep细胞中，丁酸钠（1 mmol/L）和新生霉素（0.1 mmol/L）在48小时后抑制细胞增殖，并使谷氨酰胺转运和谷氨酰胺酶活性降低超过50%。相比之下，在生长较慢、分化程度较高的HepG2和Huh-7细胞系中，这些药物分别需要72小时才能使谷氨酰胺摄取减少30%和50%。用新生霉素/丁酸钠处理所有三种细胞系也导致丙氨酸、精氨酸、亮氨酸和谷氨酰胺的转运减少30%至60%，这表明细胞增殖的抑制同样影响不同的氨基酸转运蛋白。
肝细胞转化的特征是谷氨酰胺转运和代谢显著增加。细胞增殖的抑制减弱了谷氨酰胺转运和代谢，尤其是在生长迅速、相对未分化的肝癌细胞中。由于在细胞生长抑制条件下其他氨基酸的摄取同样减少，肝癌细胞中的质膜氨基酸转运活性受细胞增殖状态的调节。
