Cellular uptake of proMMP-2:TIMP-2 complexes by the endocytic receptor megalin/LRP-2

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Matrix metalloproteinases (MMPs) are key regulators of extracellular matrix remodeling.
• Receptor-mediated endocytosis is a critical post-transcriptional regulatory mechanism for MMPs.
• Low-density lipoprotein receptor-related protein-1 (LRP-1) was previously identified to clear the MMP-2:TIMP-2 complex in fibrosarcoma cells.

Purpose of the Study:

• To investigate the role of other members of the LDL receptor family in the clearance of the MMP-2:TIMP-2 complex.
• To identify the specific receptor responsible for proMMP-2:TIMP-2 complex endocytosis in BN16 rat yolk sac cells.

Main Methods:

• Utilized receptor-associated protein (RAP) to block LRP activity.
• Employed radiolabeled proMMP-2:TIMP-2 complex for binding and uptake assays.
• Used antibodies against LRP-1 and megalin/LRP-2 to assess receptor specificity.
• Performed BIAcore analysis to confirm direct protein interactions.
• Generated conditional megalin/LRP-2 knockout mice to study in vivo relevance.

Main Results:

• Megalyn/LRP-2, not LRP-1, mediates the endocytosis of the proMMP-2:TIMP-2 complex in BN16 cells.
• Receptor-associated protein (RAP) inhibited proMMP-2:TIMP-2 binding and uptake, confirming LRP involvement.
• Antibodies against megalin/LRP-2 blocked complex binding to BN16 cells.
• BIAcore confirmed a direct interaction between megalin/LRP-2 and the proMMP-2:TIMP-2 complex.
• Conditional knockout of megalin/LRP-2 in mice led to urinary accumulation of proMMP-2 and TIMP-2.

Conclusions:

• Megalyn/LRP-2 is the primary receptor responsible for the endocytic clearance of the proMMP-2:TIMP-2 complex in rat yolk sac cells.
• This study identifies megalin/LRP-2 as a novel regulator of MMP-2 activity.
• The findings highlight the physiological significance of megalin/LRP-2 in MMP-2 regulation, with implications for pathological processes involving MMP-2.