Pemphigus is an autoimmune cutaneous disease characterized by circulating
autoantibodies that cause blistering and erosions on skin and mucous membranes. Circulating
autoantibodies bind to epidermal cell membrane and cause cell-cell detachment (
acantholysis), leading to epidermal tissue damage and cell death. The principal target of
pemphigus vulgaris autoantibodies (PV-
IgG) is desmosomal
cadherin desmoglein 3 (Dsg3), a constituent of desmosomes, mediating cell-cell adhesion. Several hypotheses for the mechanisms of
acantholysis induction by PV-
IgG exist, but the actual mechanism is not clear as yet. We have previously reported on apoptosis induction in PV-
IgG-mediated epidermal tissue and cell damage as a possible mechanism of
acantholysis and cell death (Wang et al. 2004, Apoptosis, 9:131-143). In this study we investigated the involvement of the EGFR and intracellular signal transduction pathways in the PV-
IgG-induced apoptosis. We show here that PV-
IgG induced activation/autophosphorylation of EGFR in cultured keratinocytes in vitro. The specific
tyrosine kinase inhibitor AG1478 abrogated EGFR autophosphorylation, cell death, FasL appearance and
acantholysis, all induced by PV-
IgG, in parallel, confirming the involvement of EGFR in this Fas apoptotic cascade. Activation of EGFR was followed by phosphorylation of its downstream substrates,
MAP kinase ERK and
transcription factor c-Jun, and internalization of EGFR. Pharmacological inactivation of the EGFR and ERK
kinase activities, by use of specific inhibitors
AG1478 and
PD98059 respectively, blocked PV-
IgG-induced phosphorylation of EGFR, ERK and c-Jun and cellular apoptosis, measured by flow cytometry and
caspase 3 activity. Prolonged activation of EGFR by PV-
IgG led to dramatic internalization of this receptor, possibly reducing the ability of the cell to perform survival signals. This suggests that activation of EGFR, followed by its internalization, is pivotal for intracellular apoptotic signal transduction via ERK/c-Jun pathways, leading to
acantholysis. Our experimental data indicate that the EGFR is instrumental in transducing apoptotic/acantholytic signals in keratinocytes cultures in response to PV-
IgG treatment. The acantholytic effect caused by PV-
IgG binding to
cell surface receptors begins with and depends on
cell surface receptor (EGFR) activation of intracellular signaling pathways (ERK pathway) and apoptosis induction (FasR pathway), which later lead to major cell-cell separation (
acantholysis) and cell death.