Density-dependent regulation of cell surface gamma-glutamyl transpeptidase in cultured glial cells.
Density-dependent regulation of cell surface gamma-glutamyl transpeptidase in cultured glial cells.
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培养的神经胶质细胞中细胞表面γ-谷氨酰转肽酶的密度依赖性调节。
DOI：
10.1002/jcp.1041500115
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发表时间：
1992
影响因子：
5.6
通讯作者：
DeBault,L
中科院分区：
文献类型：
--
作者：
Morgenstern,K;Hanson-Painton,O;Wang,BL;DeBault,L
先前观察到细胞表面γ-谷氨酰转肽酶比活性的下降伴随着C6神经胶质细胞的增殖。为了阐明γ-谷氨酰转肽酶下调的潜在因素(S)，考察了C6细胞密度和培养条件对细胞表面转肽酶活性水平的影响。培养24 h后，转肽酶比活力与初始培养密度呈负相关。低密度培养在接种后24小时内有诱导作用。随着培养物的增殖，在融合后，特异性转肽酶活性下降到一个普遍的低水平。γ-谷氨酰转肽酶表达下调与细胞生长速率无关，在对数增殖期最为明显。在低细胞密度下γ-谷氨酰转肽酶活性的诱导和下调不是胰酶作用的结果。用条件培养液补充低密度培养物、使用基质包被孔或定期更换生长介质以防止条件化对细胞表面活性的下降影响较小。动力学分析表明，米氏常数和反应机理不受细胞密度的影响，表明下调不是由于变构因素或酶性质的改变。细胞密度越高，细胞表面转肽的最大速度越慢，提示γ-谷氨酰转肽酶的下调与细胞表面的酶浓度有关。γ-谷氨酰转肽酶的免疫细胞化学定位显示，随着C6细胞密度的增加，γ-谷氨酰转肽酶抗原水平降低。这些结果导致我们提出细胞-细胞接触刺激γ-谷氨酰转肽酶从培养的C6神经胶质细胞表面消失。
A decline in cell surface γ‐glutamyl transpeptidase specific activity was previously observed to be concomitant with C6glial cell proliferation. To elucidate the underlying factor(s) mediating γ‐glutamyl transpeptidase down‐regulation, the effects of C6cell density and culture conditions on cell surface transpeptidase activity levels were investigated. After 24 h of culture, the transpeptidase specific activities were inversely related to the initial plating densities. The lower‐density cultures showed an induction within 24 h of plating. As the cultures proliferated, the specific transpeptidase activities declined to a common low level at postconfluency. The γ‐glutamyl transpeptidase down‐regulation was unrelated to cell growth rate and was most pronounced during logarithmic proliferation. Induction and down‐regulation of γ‐glutamyl transpeptidase activity at low cell densities were not a result of trypsinization. Supplementation of low‐density cultures with conditioned medium, use of matrix‐coated wells, or periodic replacement of growth media to prevent conditioning had minor effects on the decline of cell surface activity. Kinetic analysis showed that the Michaelis constants and the reaction mechanism were unaltered by cell density, indicating that downregulation was not due to allosteric factors or an alteration in enzyme character. A reduction in the maximal velocity of cell surface transpeptidation at higher cell densities suggested that γ‐glutamyl transpeptidase down‐regulation is related to the concentration of enzyme at the cell surface. Immunocytochemical localization of γ‐glutamyl transpeptidase demonstrated that γ‐glutamyl transpeptidase antigen levels decrease as C6cell density increases. These results led us to propose that cell‐cell contact stimulates the disappearance of γ‐glutamyl transpeptidase from the surface of cultured C6glial cells.