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 pro tein 2 (APLP2) in the healing corneal epithelium. The present study sought to investigate signal transduction pathways involved in APLP2 shedding in v itro. APLP2 was constitutively shed and released into culture medium in SV4 0-immortalized human corneal epithelial cells as assessed by Western blotti ng, 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 fact or (EGF) also induced APLP2 accumulation in culture medium. Basal APLP2 she dding as well as that induced by PMA and EGF was blocked by a mitogen-activ ated protein kinase (MAPK) kinase inhibitor, U-0126. Our results suggest th at MAPK activity accounts for basal as well as PKC- and EGF-induced APLP2 s hedding. In addition, PKC-epsilon may be involved in the induction of APLP2 shedding in corneal epithelial cells.