IRCM, Institut de Recherche en Cancérologie de Montpellier, Montpellier, France.
Oncogene. 2012 Jun 28;31(26):3202-12. doi: 10.1038/onc.2011.501. Epub 2011 Nov 14.
The aspartic protease cathepsin-D (cath-D) is a marker of poor prognosis in breast cancer that is overexpressed and hypersecreted by human breast cancer cells. Secreted pro-cath-D binds to the extracellular domain of the β-chain of the LDL receptor-related protein-1 (LRP1) in fibroblasts. The LRP1 receptor has an 85-kDa transmembrane β-chain and a noncovalently attached 515-kDa extracellular α-chain. LRP1 acts by (1) internalizing many ligands via its α-chain, (2) activating signaling pathways by phosphorylating the LRP1β-chain tyrosine and (3) modulating gene transcription by regulated intramembrane proteolysis (RIP) of its β-chain. LRP1 RIP involves two cleavages: the first liberates the LRP1 ectodomain to give a membrane-associated form, LRP1β-CTF, and the second generates the LRP1β-intracellular domain, LRP1β-ICD, that modulates gene transcription. Here, we investigated the endocytosis of pro-cath-D by LRP1 and the effect of pro-cath-D/LRP1β interaction on LRP1β tyrosine phosphorylation and/or LRP1β RIP. Our results indicate that pro-cath-D was partially endocytosed by LRP1 in fibroblasts. However, pro-cath-D and ectopic cath-D did not stimulate phosphorylation of the LRP1β-chain tyrosine. Interestingly, ectopic cath-D and its catalytically inactive (D231N)cath-D, and pro-(D231N)cath-D all significantly inhibited LRP1 RIP by preventing LRP1β-CTF production. Thus, cath-D inhibits LRP1 RIP independently of its catalytic activity by blocking the first cleavage. As cath-D triggers fibroblast outgrowth by LRP1, we propose that cath-D modulates the growth of fibroblasts by inhibiting LRP1 RIP in the breast tumor microenvironment.
天冬氨酸蛋白酶组织蛋白酶 D（cath-D）是乳腺癌预后不良的标志物，在乳腺癌细胞中过度表达和过度分泌。分泌型 pro-cath-D 与成纤维细胞中 LDL 受体相关蛋白-1（LRP1）β 链的细胞外结构域结合。LRP1 受体具有 85kDa 的跨膜β链和非共价连接的 515kDa 细胞外α链。LRP1 通过以下方式发挥作用：（1）通过其α链内化许多配体，（2）通过磷酸化 LRP1β 链酪氨酸激活信号通路，（3）通过其β链的调节膜内蛋白水解（RIP）调节基因转录。LRP1 RIP 涉及两个裂解：第一个裂解释放 LRP1 的细胞外结构域，形成膜相关形式 LRP1β-CTF，第二个裂解生成 LRP1β-细胞内结构域，LRP1β-ICD，调节基因转录。在这里，我们研究了 pro-cath-D 通过 LRP1 的内吞作用以及 pro-cath-D/LRP1β 相互作用对 LRP1β 酪氨酸磷酸化和/或 LRP1β RIP 的影响。我们的结果表明，pro-cath-D 在成纤维细胞中部分被 LRP1 内吞。然而，pro-cath-D 和异位 cath-D 并没有刺激 LRP1β 链酪氨酸的磷酸化。有趣的是，异位 cath-D 及其催化失活（D231N）cath-D 和 pro-（D231N）cath-D 都显著抑制了 LRP1 RIP，阻止了 LRP1β-CTF 的产生。因此，cath-D 通过阻止第一次裂解，独立于其催化活性抑制 LRP1 RIP。由于 cath-D 通过 LRP1 触发成纤维细胞的生长，我们提出 cath-D 通过抑制乳腺癌肿瘤微环境中的 LRP1 RIP 来调节成纤维细胞的生长。
