Truncation of annexin A1 is a regulatory lever for linking epidermal growth factor signaling with cytosolic phospholipase A₂ in normal and malignant squamous epithelial cells

Regulation of cell growth and apoptosis is one of the pleiotropic functions of annexin A1 (ANXA1). Although previous reports on the overexpression of ANXA1 in many human cancers and on growth suppression and/or induction of apoptosis by ANXA1 may indicate the tumor-suppressive nature of ANXA1, molecular mechanisms of the function of ANXA1 remain largely unknown. Here we provide evidence that ANXA1 mechanistically links the epidermal growth factor-triggered growth signal pathway with cytosolic phospholipase A₂ (cPLA ₂), an initiator enzyme of the arachidonic acid cascade, through interaction with S100A11 in normal human keratinocytes (NHK). Ca ²⁺-dependent binding of S100A11 to ANXA1 facilitated the binding of the latter to cPLA₂, resulting in inhibition of cPLA₂ activity, which is essential for the growth of NHK. On exposure of NHK to epidermal growth factor, ANXA1 was cleaved solely at Trp¹², and this cleavage was executed by cathepsin D. In squamous cancer cells, this pathway was shown to be constitutively activated. The newly found mechanistic intersection may be a promising target for establishing new measures against human cancer and other cell growth disorders.