Proteolytic Processing of Angiopoietin-like Protein 4 by Proprotein Convertases Modulates Its Inhibitory Effects on Lipoprotein Lipase Activity

Abstract

Angiopoietin-like protein 4 (ANGPTL4) has been associated with a variety of diseases. It is known as an endogenous inhibitor of lipoprotein lipase (LPL), and it modulates lipid deposition and energy homeostasis. ANGPTL4 is cleaved by unidentified protease(s), and the biological importance of this cleavage event is not fully understood with respect to its inhibitory effect on LPL activity. Here, we show that ANGPTL4 appears on the cell surface as the full-length form, where it can be released by heparin treatment in culture and in vivo. ANGPTL4 protein is then proteolytically cleaved into several forms by proprotein convertases (PCs). Several PCs, including furin, PC5/6, paired basic amino acid-cleaving enzyme 4, and PC7, are able to cleave human ANGPTL4 at a consensus site. PC-specific inhibitors block the processing of ANGPTL4. Blockage of ANGPTL4 cleavage reduces its inhibitory effects on LPL activity and decreases its ability to raise plasma triglyceride levels. In summary, the cleavage of ANGPTL4 by these PCs modulates its inhibitory effect on LPL activity.Angiopoietin-like protein 4 (ANGPTL4) is also known as hepatic fibrinogen/angiopoietin-related protein, fasting-induced adipose factor, peroxisome proliferator-activated receptors, and ␥-angiopoietin-related protein. It is one of the seven members of the ANGPTL family (ANGPTL1-7). Mainly produced in hepatocytes in humans and adipocytes in mice, ANGPTL4 exerts its biological effects by means of autocrine/ paracrine and endocrine processes. ANGPTL4 has been implicated in a variety of diseases, including cardiovascular disease (1, 2), cancer metastasis (3), obesity (4), diabetes (5), wound repair (6, 7), inflammation (8), and arthritis (9).ANGPTL4 is a fusion protein consisting of an N-terminal coiled-coil domain and a C-terminal fibrinogen-like domain.These two domains have been shown to have distinct biological functions (10). The N-terminal domain is responsible for the inhibitory effects on LPL, 4 converting the active form of LPL into an inactive form (11), and the C terminus mediates its antiangiogenic functions (12). Interestingly, these two domains are separated by a short linker that can be cleaved after secretion. The cleavage phenomenon has been shown to occur in humans as well as in rodents (13,14). Cleavage of ANGPTL4 appears to be tissue-dependent in humans; liver secretes cleaved ANGPTL4, whereas adipose tissue secretes the fulllength form (14).The physiological relevance of the proteolytic processing of ANGPTL4 is largely unknown. In a human study, treatment with fenofibrate, a potent peroxisome proliferator-activated receptor-␣ agonist, markedly increased plasma levels of cleaved ANGPTL4. On this basis, it was proposed that the cleaved form of ANGPTL4 may have specific functions (14). There is evidence that the antiangiogenic activity of ANGPTL4 is regulated by an interaction of its coiled-coil domain with heparan sulfate proteoglygans (HSPGs) (18). This may be due to an ability of the N-terminal domain to facilitate the interaction between t...

Angiopoietin-like 4 Modifies the Interactions between Lipoprotein Lipase and Its Endothelial Cell Transporter GPIHBP1

“…In agreement with what has been reported previously (36,37), the N-terminal portion of ANGPTL4 was a more potent inactivator of LPL than full-length ANGPTL4 (Fig. 9B).…”

Proprotein convertase furin/PCSK3 and atherosclerosis: New insights and potential therapeutic targets

“…Like EL, ANGPTL 3 and 4, which have a consensus PC recognition site, can inhibit LPL activity by enhancing its cleavage. Lei et al [17] found that cleaved ANGPTL4 can be detected in furindeficient cells, and furin overexpression only had moderate effects on ANGPTL 4 cleavage, suggesting that furin is not the only PC that cleaves ANGPTL4. They identified that several PCs, including furin, PC5/6 and PACE4 but not PCSK9, are responsible for ANGPTL4 cleavage, resulting in the production of the N-terminus of ANGPTL4, a more potent LPL inhibitor.…”

Angiopoietin-like Protein 4 Inhibition of Lipoprotein Lipase

“…The N-terminal domain is a coiled-coil that mediates oligomerization of the protein, and the C-terminal portion is a fibrinogen-like domain (18). After ANGPTL4 is secreted, these domains are cleaved apart by the action of pro-protein convertases (18,19). The N-terminal domain inhibits LPL activity, and cleavage of the two domains enhances this inhibition (18,20,21).…”