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Tissue distribution and subcellular localization of rabbit liver metalloendopeptidase
K Nakagawa1, S Kawabata, Y Nakashima
1Department of Pathology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Abstract:
We have previously isolated rabbit liver microsomal metalloendopeptidase (MEP) as a candidate for the processing enzyme of vitamin K-dependent plasma proteins. A cDNA coding for MEP has revealed that it is structurally related to metalloendopeptidase-24.15, which catalyzes the proteolytic processing of several bioactive peptides. In this study we examined the tissue distribution and subcellular localization of MEP by light and electron microscopic immunohistochemical methods, in addition to Northern blot analysis. Chicken polyclonal antibodies were raised by using synthetic peptides AG1 (Met31-Asn46) and AG3 (Asp537-Gly551) derived from the sequence of MEP. Both anti-AG1 and anti-AG3 antibodies reacted specifically with MEP, as judged by Western blotting and immunohistochemical methods. Both antibodies gave an identical staining distribution, which was localized on the luminal cell surfaces and in the cytoplasm of the following organs: liver, brain, lungs, kidneys, esophagus, stomach, duodenum, pancreas, placenta, epididymis, uterus, ovary, and oviduct. Northern blot analysis revealed that the expression of MEP mRNA is similar to its immunohistochemical distribution except in the heart. These results suggest that MEP may participate more closely in a degradation role in peptide metabolism in various tissues than in a processing role of the proprotein, like metalloendopeptidase-24.15.
Insights
Metalloendopeptidase (MEP) is found in various tissues, suggesting a broader role in peptide degradation rather than just processing vitamin K-dependent proteins.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Metalloendopeptidase (MEP) was previously identified in rabbit liver microsomes as a potential enzyme for processing vitamin K-dependent plasma proteins.
- MEP shares structural similarities with metalloendopeptidase-24.15, an enzyme involved in the proteolytic processing of bioactive peptides.
Purpose of the Study:
- To investigate the tissue distribution and subcellular localization of Metalloendopeptidase (MEP).
- To compare the expression patterns of MEP mRNA with its protein localization.
Main Methods:
- Immunohistochemical analysis using light and electron microscopy with chicken polyclonal antibodies against synthetic MEP peptides (AG1 and AG3).
- Western blotting to confirm antibody specificity.
- Northern blot analysis to assess MEP mRNA expression levels.
Main Results:
- Both anti-AG1 and anti-AG3 antibodies specifically recognized MEP.
- MEP protein was localized on the luminal cell surfaces and in the cytoplasm of multiple organs, including liver, brain, lungs, kidneys, and reproductive tissues.
- MEP mRNA expression mirrored the protein distribution, with the exception of the heart.
Conclusions:
- The widespread tissue distribution and subcellular localization of MEP suggest a significant role in peptide metabolism, potentially more in degradation than in proprotein processing.
- MEP's function may extend beyond the processing of vitamin K-dependent proteins, indicating a broader involvement in endogenous peptide turnover.