A role for MAP kinase in regulating ectodomain shedding of APLP2 in corneal epithelial cells.

We previously reported an increased secretion of amyloid precursor-like protein 2 (APLP2) in the healing corneal epithelium. The present study sought to investigate signal transduction pathways involved in APLP2 shedding in vitro. APLP2 was constitutively shed and released into culture medium in SV40-immortalized human corneal epithelial cells as assessed by Western blotting, flow cytometry, and indirect immunofluorescence. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) caused significant increases in APLP2 shedding. This was inhibited by staurosporine and a PKC-epsilon-specific, N-myristoylated peptide inhibitor. Epidermal growth factor (EGF) also induced APLP2 accumulation in culture medium. Basal APLP2 shedding as well as that induced by PMA and EGF was blocked by a mitogen-activated protein kinase (MAPK) kinase inhibitor, U-0126. Our results suggest that MAPK activity accounts for basal as well as PKC- and EGF-induced APLP2 shedding. In addition, PKC-epsilon may be involved in the induction of APLP2 shedding in corneal epithelial cells.