Protein processing by the placental protease, cathepsin P

Area of Science:

• Biochemistry
• Proteomics
• Cell Biology

Background:

• Cathepsin P belongs to placentally expressed cathepsins (PECs), closely related to the broad-specificity cathepsin L.
• PECs offer a unique model to study proteolytic functions in the mammalian placenta.
• Cathepsin P exhibits a restricted substrate preference for hydrophobic amino acids.

Purpose of the Study:

• To identify and characterize substrates of Cathepsin P.
• To investigate the role of Cathepsin P in the processing of endoplasmic reticulum (ER) proteins.
• To explore the potential function of Cathepsin P in trophoblast giant cell differentiation.

Main Methods:

• Proteomic techniques including 2D-difference gel electrophoresis, trypsin digestion, and MALDI MS/MS were employed.
• Recombinant Cathepsin P was incubated with rat choriocarcinoma (Rcho-1) cell proteins.
• Western blotting and immunohistochemistry were used to validate substrate processing and localization.

Main Results:

• Two ER proteins, gp96 and calreticulin, were identified as potential substrates of Cathepsin P.
• Cathepsin P was shown to process calreticulin and gp96 by removing their C-terminal KDEL ER retention signal.
• Cathepsin P co-localizes with calreticulin in Rcho-1 cells, and extracellular calreticulin induces Rcho-1 cell differentiation.

Conclusions:

• Cathepsin P plays a role in the post-translational modification of ER proteins, specifically calreticulin and gp96.
• The processing of calreticulin by Cathepsin P may be involved in the secretion of calreticulin during trophoblast giant cell differentiation.
• Cathepsin P's function in processing secreted proteins highlights its importance in placental biology.