Mesotrypsin and caspase-14 participate in prosaposin processing: potential relevance to epidermal permeability barrier formation

J Biol Chem. 2014 Jul 18;289(29):20026-38. doi: 10.1074/jbc.M113.543421. Epub 2014 May 28.


A proteomics-based search for molecules interacting with caspase-14 identified prosaposin and epidermal mesotrypsin as candidates. Prosaposin is a precursor of four sphingolipid activator proteins (saposins A-D) that are essential for lysosomal hydrolysis of sphingolipids. Thus, we hypothesized that caspase-14 and mesotrypsin participate in processing of prosaposin. Because we identified a saposin A sequence as an interactor with these proteases, we prepared a specific antibody to saposin A and focused on saposin A-related physiological reactions. We found that mesotrypsin generated saposins A-D from prosaposin, and mature caspase-14 contributed to this process by activating mesotrypsinogen to mesotrypsin. Knockdown of these proteases markedly down-regulated saposin A synthesis in skin equivalent models. Saposin A was localized in granular cells, whereas prosaposin was present in the upper layer of human epidermis. The proximity ligation assay confirmed interaction between prosaposin, caspase-14, and mesotrypsin in the granular layer. Oil Red staining showed that the lipid envelope was significantly reduced in the cornified layer of skin from saposin A-deficient mice. Ultrastructural studies revealed severely disorganized cornified layer structure in both prosaposin- and saposin A-deficient mice. Overall, our results indicate that epidermal mesotrypsin and caspase-14 work cooperatively in prosaposin processing. We propose that they thereby contribute to permeability barrier formation in vivo.

Keywords: Bar; Caspase; Caspase,; Cell Differentiation; Kallikrein; Keratinocyte; Protein Processing.

MeSH terms

  • Animals
  • Caspases / genetics
  • Caspases / metabolism*
  • Cells, Cultured
  • Gene Knockdown Techniques
  • Humans
  • Keratinocytes / metabolism
  • Mice
  • Mice, Knockout
  • Models, Biological
  • Permeability
  • Protein Processing, Post-Translational
  • RNA, Small Interfering / genetics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Saposins / deficiency
  • Saposins / genetics
  • Saposins / metabolism*
  • Skin / metabolism*
  • Skin / ultrastructure
  • Trypsin / genetics
  • Trypsin / metabolism*


  • PSAP protein, human
  • Psap protein, mouse
  • RNA, Small Interfering
  • Recombinant Proteins
  • Saposins
  • saposin A, mouse
  • PRSS3 protein, human
  • Trypsin
  • CASP14 protein, human
  • Casp14 protein, mouse
  • Caspases