Isidoro C, Baccino F M, Hasilik A
Dipartimento di Medicina ed Oncologia Sperimentale, University of Turin, Italy.
Int J Cancer. 1997 Mar 4;70(5):561-6. doi: 10.1002/(sici)1097-0215(19970304)70:5<561::aid-ijc12>3.0.co;2-g.
Synthesis, processing and sorting of pro-cathepsin D (proCD), the precursor of a lysosomal protease involved in tumor-cell proliferation and invasion, were compared in various human tumor cell lines. In cultures of HepG2, HT29 and MCF7 cells the extracellular CD activity was up to 10 times higher than in cultures of U937 and MG63 cells. Ammonium chloride, which disrupts the pH-dependent receptor-mediated transport of lysosomal enzymes, exerted a differential effect on the secretion of CD activity in these cells. As judged by metabolic labeling and immunoprecipitation, the secretion of CD synthesized in 24 hr in MG63 and U937 cells was enhanced 4- to 10-fold by ammonium chloride, while it was only slightly increased in HepG2, HT29 and MCF7 cells. In all tumor cells examined, a portion of proCD was segregated into the endosomal-lysosomal pathway in the presence of ammonium chloride. However, the intralysosomal maturation of CD was only inhibited by this drug in HT29 and MCF7 cells. The Golgi-associated processing of proCD, leading to the synthesis of uncovered phosphomannosyl groups, proceeded with comparable efficiency in all tumor cells examined. These results suggest that hypersecretion of proCD in HepG2, HT29 and MCF7 cells is linked to transport mechanisms, as yet unidentified, which are independent of mannose-6-phosphate.
在多种人类肿瘤细胞系中，对参与肿瘤细胞增殖和侵袭的溶酶体蛋白酶组织蛋白酶D原（proCD）的合成、加工和分选进行了比较。在HepG2、HT29和MCF7细胞培养物中，细胞外CD活性比U937和MG63细胞培养物中的高10倍。氯化铵可破坏溶酶体酶依赖pH的受体介导转运，对这些细胞中CD活性的分泌产生不同影响。通过代谢标记和免疫沉淀判断，氯化铵使MG63和U937细胞中24小时内合成的CD分泌增加4至10倍，而在HepG2、HT29和MCF7细胞中仅略有增加。在所有检测的肿瘤细胞中，在氯化铵存在的情况下，一部分proCD被分选到内体-溶酶体途径。然而，该药物仅在HT29和MCF7细胞中抑制CD在溶酶体内的成熟。在所有检测的肿瘤细胞中，导致未覆盖磷酸甘露糖基团合成的proCD与高尔基体相关的加工效率相当。这些结果表明，HepG2、HT29和MCF7细胞中proCD的高分泌与尚未明确的转运机制有关，该机制独立于甘露糖-6-磷酸。
