N-terminal processing is essential for release of epithin, a mouse type II membrane serine protease.
Epithin was originally identified as a mouse type II membrane serine protease. Its human orthologue membrane type-serine protease 1 (MT-SP1)/matriptase has been reported to be localized on the plasma membrane. In addition, soluble forms of matriptase were isolated from human breast milk and breast cancer cell-conditioned medium. In this paper, we report a processing mechanism that appears to be required for the release of epithin. CHO-K1 or COS7 cells transfected with single full-length epithin cDNA generated two different-sized proteins in cell lysates, 110 and 92 kDa. The 92-kDa epithin was found to be an N-terminally truncated form of the 110-kDa epithin, and it was the only form detected in the culture medium. The 92-kDa epithin was also found on the cell surface, where it was anchored by the N-terminal fragment. The results of in vivo cell labeling experiments indicate that the 110-kDa epithin is rapidly processed to the 92-kDa epithin. Using site-directed mutagenesis experiments, we identified Gly(149) of the GSVIA sequence in epithin as required for the processing and release of the protein. These results suggest that N-terminal processing of epithin at Gly(149) is a necessary prerequisite step for release of the protein.
Cho
E G
EG
School of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea.
Kim
M G
MG
Kim
C
C
Kim
S R
SR
Seong
I S
IS
Chung
C
C
Schwartz
R H
RH
Park
D
D
D000818:Animals; D019921:Biotinylation; D016466:CHO Cells; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology*; D006224:Cricetinae; D017077:Culture Media, Conditioned / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D004330:Drosophila; D010450:Endopeptidases / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D005998:Glycine / Q000737:chemistry; D008565:Membrane Proteins; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism / Q000494:pharmacology
D017077:Culture Media, Conditioned; D018076:DNA, Complementary; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; D010450:Endopeptidases; D012697:Serine Endopeptidases; C485595:matriptase; C118992:St14 protein, mouse; D014357:Trypsin; D005998:Glycine