Berg R A, Schwartz M L, Crystal R G
Proc Natl Acad Sci U S A. 1980 Aug;77(8):4746-50. doi: 10.1073/pnas.77.8.4746.
Confluent cultures of human fetal lung fibroblasts degrade approximately 10% of their newly synthesized collagen within the cell prior to secretion. This basal level of intracellular degradation could not be inhibited by colchicine or cytochalasin B, inhibitors of microtubular and microfilament function, respectively, or by N(alpha)-p-tosyl-L-lysine chloromethyl ketone, chloroquine, or NH(4)Cl, inhibitors of lysosomal enzymes. In contrast, cells in early logarithmic growth degrade approximately 30% of their newly synthesized collagen. This enhanced degradation of collagen in rapidly growing cells could be suppressed by inhibitors of lysosomal proteases and partially inhibited by disrupters of microtubular and microfilament function. A significant proportion of the collagen synthesized by these cultures contained prolyl residues that were incompletely hydroxylated. Because such collagen is "defective" (i.e., not capable of assuming a triple helical conformation), the results suggest that enhanced intracellular degradation may be a mechanism by which cells control the quality of collagen they produce. To test this hypothesis, confluent cells were incubated with the proline analog cis-4-hydroxyproline; such cells demonstrated enhanced collagen degradation that could be inhibited by agents that interfere with lysosomal, microtubular, or microfilament function. Because collagen containing cis-4-hydroxyproline cannot form a perfect triple helix, the data are consistent with the concept that defective collagen is recognized by cells and degraded prior to secretion. Thus, the proportion of newly synthesized collagen that undergoes intracellular degradation seems to be modulated, in part, by the conformation of the collagen molecule. Intracellular proteolysis may represent a means by which collagen-producing cells regulate the quality and quantity of collagen available for extracellular function. Although the exact mechanism of intracellular collagen degradation is unknown, the data presented here are consistent with a role for lysosomal proteases in this process.
人胎儿肺成纤维细胞的汇合培养物在分泌前会在细胞内降解约10%新合成的胶原蛋白。这种基础水平的细胞内降解不能被秋水仙碱或细胞松弛素B（分别为微管和微丝功能的抑制剂）或N（α）-对甲苯磺酰-L-赖氨酸氯甲基酮、氯喹或氯化铵（溶酶体酶的抑制剂）抑制。相比之下，处于对数生长早期的细胞会降解约30%新合成的胶原蛋白。快速生长细胞中胶原蛋白这种增强的降解可被溶酶体蛋白酶抑制剂抑制，并被微管和微丝功能破坏剂部分抑制。这些培养物合成的相当一部分胶原蛋白含有不完全羟化的脯氨酰残基。由于这种胶原蛋白是“有缺陷的”（即不能形成三螺旋构象），结果表明增强的细胞内降解可能是细胞控制其产生的胶原蛋白质量的一种机制。为了验证这一假设，将汇合细胞与脯氨酸类似物顺式-4-羟脯氨酸一起孵育；这类细胞表现出增强的胶原蛋白降解，且可被干扰溶酶体、微管或微丝功能的试剂抑制。由于含有顺式-4-羟脯氨酸的胶原蛋白不能形成完美的三螺旋，数据与有缺陷的胶原蛋白在分泌前被细胞识别并降解的概念一致。因此，新合成的胶原蛋白发生细胞内降解的比例似乎部分受胶原蛋白分子构象的调节。细胞内蛋白水解可能是产生胶原蛋白的细胞调节可用于细胞外功能的胶原蛋白质量和数量的一种方式。虽然细胞内胶原蛋白降解的确切机制尚不清楚，但此处呈现的数据与溶酶体蛋白酶在这一过程中的作用一致。
