Tanabe S, Sherman H, Smith L, Yang L A, Fleming R, Hay R
Department of Pathology, University of Chicago, Illinois 60637.
In Vitro Cell Dev Biol. 1989 Dec;25(12):1129-40. doi: 10.1007/BF02621264.
Cultured McA-RH7777 rat hepatoma cells actively synthesize and secrete plasma lipoproteins. However, synthesis of [14C]triglyceride declines monotonically throughout the early growth period and remains low in postconfluent cultures; and net secretion of [14C]triglyceride is 10-fold more efficient in logarithmically growing cultures than in postconfluent cultures. Secretion of apolipoproteins associated with very low density and low density lipoproteins is selectively reduced in postconfluent cultures. The temporal reductions in [14C]triglyceride production are related more strongly to increasing cell concentration (cells/cm3 medium) than to increasing cell density (cells/cm2 growth surface). We have allowed cells to grow either retained within small circular corrals or unrestricted in culture dishes. When seeded at equal density (10(4) cells/cm2) but at one-fifth the cell concentration, corralled cells synthesize twice as much [14C]triglyceride per cell after 2 and 4 d, and are 10 times as efficient in [14C]triglyceride secretion by 6 d of growth, as noncorralled cells. When seeded at equal cell concentration (10(5) cells/dish) but at 5 times the cell density, corralled cells are only 20% less efficient at [14C]triglyceride synthesis and secretion than noncorralled cells. Conditioned medium depresses synthesis and secretion efficiency of [14C]triglyceride. Orotic acid exposure also inhibits synthesis of [14C]triglyceride and secretion of certain [35S]apolipoproteins in early cultures, but it has no significant effect on late cultures. We conclude that diffusion-mediated events are important regulators of triglyceride and apolipoprotein production in growing rat hepatoma cells, but that events associated with formation of cell-to-cell contacts play a minor role in regulation of plasma lipoprotein biogenesis.
培养的McA-RH7777大鼠肝癌细胞能活跃地合成和分泌血浆脂蛋白。然而，在整个早期生长阶段，[14C]甘油三酯的合成单调下降，在汇合后培养物中仍维持在低水平；并且在对数生长期培养物中，[14C]甘油三酯的净分泌效率比汇合后培养物高10倍。与极低密度脂蛋白和低密度脂蛋白相关的载脂蛋白的分泌在汇合后培养物中选择性降低。[14C]甘油三酯产生的时间性降低与细胞浓度（细胞/立方厘米培养基）增加的相关性比与细胞密度（细胞/平方厘米生长表面）增加的相关性更强。我们让细胞要么在小圆形围栏内生长，要么在培养皿中不受限制地生长。当以相等密度（10(4)个细胞/平方厘米）接种但细胞浓度为五分之一时，围栏内的细胞在2天和4天后每个细胞合成的[14C]甘油三酯是未围栏细胞的两倍，到生长6天时，[14C]甘油三酯分泌效率是未围栏细胞的10倍。当以相等细胞浓度（10(5)个细胞/培养皿）接种但细胞密度为5倍时，围栏内的细胞在[14C]甘油三酯合成和分泌方面比未围栏细胞仅低20%。条件培养基会降低[14C]甘油三酯的合成和分泌效率。在早期培养物中，乳清酸暴露也会抑制[14C]甘油三酯的合成和某些[35S]载脂蛋白的分泌，但对后期培养物没有显著影响。我们得出结论，扩散介导的事件是生长中的大鼠肝癌细胞中甘油三酯和载脂蛋白产生的重要调节因子，但与细胞间接触形成相关的事件在血浆脂蛋白生物合成的调节中起次要作用。
