Cathepsin D is partly endocytosed by the LRP1 receptor and inhibits LRP1-regulated intramembrane proteolysis

Abstract

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 procath-D binds to the extracellular domain of the b-chain of the LDL receptor-related protein-1 (LRP1) in fibroblasts. The LRP1 receptor has an 85-kDa transmembrane b-chain and a noncovalently attached 515-kDa extracellular a-chain. LRP1 acts by (1) internalizing many ligands via its a-chain, (2) activating signaling pathways by phosphorylating the LRP1b-chain tyrosine and (3) modulating gene transcription by regulated intramembrane proteolysis (RIP) of its b-chain. LRP1 RIP involves two cleavages: the first liberates the LRP1 ectodomain to give a membrane-associated form, LRP1b-CTF, and the second generates the LRP1b-intracellular domain, LRP1b-ICD, that modulates gene transcription. Here, we investigated the endocytosis of pro-cath-D by LRP1 and the effect of pro-cath-D/LRP1b interaction on LRP1b tyrosine phosphorylation and/or LRP1b 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 LRP1b-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 LRP1b-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.

Lysosomal exocytosis and caspase-8 mediated apoptosis in UVA-irradiated keratinocytes

“…We found lysosomal exocytosis to result in the release of cathepsin D into the extracellular space, which has also been reported to occur in keratinocytes exposed to ionophores (Jans et al, 2004). Interestingly, pro-cathepsin D has been shown to have a mitogenic effect on fibroblasts when released extracellularly (Derocq et al, 2012). Cathepsins also promote tumorigenesis by stimulating tumor growth, enhancing angiogenesis and facilitating invasion (Gocheva et al, 2006).…”

Low‐density lipoprotein receptor‐related protein 1 is a novel modulator of radial glia stem cell proliferation, survival, and differentiation

“…On the one hand, LRP1 can stimulate proliferation of mouse embryonic fibroblasts upon treatment with LRP1 ligands by stimulating downstream pro-proliferative signaling. (Derocq et al 2012; Kozlova et al 2015; Muratoglu et al 2010). On the other hand, LRP1 can suppress lung tumor cell, hepatic stellate cell and smooth muscle cell proliferation, most likely by endocytic uptake of pro-proliferative molecules (Boucher et al 2003; Llorente-Cortes et al 2012; Meng et al 2011).…”

Cathepsin D and its newly identified transport receptor SEZ6L2 can modulate neurite outgrowth

“…β-glucocerebrosidase, a non-phosphorylated enzyme, uses the lysosomal membrane protein LIMPII as a transport receptor (Reczek et al, 2007). Sortilin is involved in the sorting of prosaposin, GM2AP, acid sphingomyelinase, cathepsin H and cathepsin D in selected cell types (Lefrancois et al, 2003;Canuel et al, 2008;Wähe et al, 2010) and, in fibroblasts, cathepsin B and D can be captured by the membrane proteins LRP1 and LDLR (Derocq et al, 2012;Markmann et al, 2015). We now report a role of the type 1 transmembrane protein SEZ6L2 in the Man-6-Pindependent transport of cathepsin D in neurons.…”