Human MMP2 adenoviral particles

The low-density lipoprotein receptor (LDLR) catalyzes the uptake of LDL cholesterol by the liver and peripheral organs. The function of the LDLR is antagonized by the pro-protein convertase subtilisin/kexin type 9 (PCSK9), which binds to the LDLR on the plasma membrane and induces its degradation. Here, researchers report that matrix metalloproteinase 2 (MMP-2) interacts with and cleaves PCSK9, as confirmed by proteomics, chemical cross-linking, blue native PAGE, and domain-specific antibody Western blot analyses. Furthermore, MMP-2 overexpression renders Hepa1-c1c7 cells resistant to PCSK9-induced LDLR degradation. Data suggest that pathological MMP-2 overexpression may protect the LDLR from PCSK-9-induced degradation.

The positive feedback of the SREBP-2 pathway is dependent on plasma PCSK9, a circulating LDLR ligand that binds to the LDLR extracellular domain and reroutes LDLR from the circulating pathway to the lysosome, where it is degraded. In cells stably expressing LDLR, addition of recombinant human (rh) PCSK-9 induces LDLR degradation. However, overexpression of human MMP-2 prevents PCSK9-induced LDLR degradation (Figure 1) and inhibits transcription of SREBP-2 and target genes.

Figure 1. MMP-2 protects LDLR from PCSK9-induced degradation. (A) Hepa1-c1c7 (LDLR-positive) cells were plated in 24-well plates in complete medium containing 10% FBS. 70% confluent cells were transduced with green fluorescent protein adenovirus (AdGFP) or human MMP-2 encoding adenovirus (AdMMP-2). Both qRT-PCR and gelatin zymography analysis showed that human MMP-2 activity was overexpressed in AdMMP-2-transduced cells. (B) 24 hours after transduction of AdGFP or AdMMP-2, the medium was replaced with serum-free medium supplemented with 4% BSA. After 16 hours, rhPCSK9 or vehicle was added. After 4 hours, cells were harvested and lysed. Lysates were analyzed by western blot with LDLR antibodies. (Wang X, et al., 2015)