Cathepsin-D affects multiple tumor progression steps in vivo: proliferation, angiogenesis and apoptosis

Abstract

Cathepsin-D is an independent marker of poor prognosis in human breast cancer. We previously showed that human wild-type cathepsin-D, as well as its mutated form devoid of proteolytic activity stably transfected in 3Y1-Ad12 cancer cells, stimulated tumor growth. To investigate the mechanisms by which human cathepsin-D and its catalytically-inactive counterpart promoted tumor growth in vivo, we quantified the expression of proliferating cell nuclear antigen, the number of blood vessels and of apoptotic cells in 3Y1-Ad12 tumor xenografts. We first verified that both human wild-type and mutated cathepsin-D were expressed at a high level in cathepsin-D xenografts, whereas no human cathepsin-D was detected in control xenografts. Our immunohistochemical studies then revealed that both wild-type cathepsin-D and catalytically-inactive cathepsin-D, increased proliferating cell nuclear antigen expression and tumor angiogenesis. Interestingly, wild-type cathepsin-D significantly inhibited tumor apoptosis, whereas catalytically-inactive cathepsin-D did not. We therefore propose that human cathepsin-D stimulates tumor growth by acting -directly or indirectly -as a mitogenic factor on both cancer and endothelial cells independently of its catalytic activity. Our overall results provide the first mechanistic evidences on the essential role of cathepsin-D at multiple tumor progression steps, affecting cell proliferation, angiogenesis and apoptosis.

Stress-induced apoptosis is impaired in cells with a lysosomal targeting defect but is not affected in cells synthesizing a catalytically inactive cathepsin D

“…Or, conversely, has it got some mitogenic functions as noticed in cancer cells. 50,52 Clearly, further investigations will be required to answer this question. Seemingly conflicting reports on the role of cathepsin D in apoptosis refer to different systems.…”

“…50 In addition, transfection of embryonic rat tumorigenic cells with an expression vector encoding human cathepsin D was reported to increase their metastatic potential in nude mice. 51 Conversely, downregulation of cathepsin D expression by antisense gene transfer was described to inhibit tumor growth and experimental lung metastasis of human breast cancer cells.…”

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

“…We checked these results by investigating the effect of recombinant proteolytically inactive D231N pro-cath-D on the production of endogenous LRP1b-CTF in HMF .1(-) plasmids using Lipofectamine (Gibco-BRL, Life Technologies SAS, Villebon sur Yvette, France). pcDNA3.1(-)cath-D expression plasmid encoding human pre-pro-cath-D has previously been described (Vignon et al, 1986;Glondu et al, 2001Glondu et al, , 2002Berchem et al, 2002;Laurent-Matha et al, 2005;Hu et al, 2008). fibroblasts ( Figure 3C, panel a).…”

“…Cath-D affects both the cancer cells and the stromal cells of the tumor microenvironment. Human pre-pro-cath-D cDNA transfected in cancer cells promotes cancer cell proliferation, tumor angiogenesis, and tumor growth and metastasis (Glondu et al, 2001;Berchem et al, 2002). Human pre-pro-cath-D cDNA transfected in cath-DÀ/À MEF (mouse embryonic fibroblast) cells induces fibroblast outgrowth (LaurentMatha et al, 2005).…”

“…Human secreted pro-cath-D stimulates breast cancer cell proliferation (Vignon et al, 1986;Fusek and Vetvicka, 1994;Vetvicka et al, 1994;Ohri et al, 2008), fibroblast outgrowth (Laurent-Matha et al, 2005) and angiogenesis (Hu et al, 2008). We have shown that a mutated catalytically inactive version of cath-D (D231N) is still mitogenic for tumor cells and fibroblasts (Glondu et al, 2001;Berchem et al, 2002;Laurent-Matha et al, 2005). We recently discovered that pro-cath-D is the first ligand that binds to the extracellular domain of the b-chain of the LDL receptor-related protein-1 (LRP1) in fibroblasts (Beaujouin et al, 2010).…”