Activation of kinin B receptor triggers differentiation of cultured human keratinocytes

Background Keratinocyte life span is modulated by receptors that control proliferation and differentiation, key processes during cutaneous tissue repair. The kinin B₁ receptor (B₁R) has been reported in normal and pathological human skin, but so far there is no information about its role in keratinocyte biology. Objectives To determine the consequence of kinin B₁R stimulation on tyrosine phosphorylation, a key signalling mechanism involved in keratinocyte proliferation and differentiation. Methods Subconfluent primary cultures of human keratinocytes were used to investigate tyrosine phosphorylation, epidermal growth factor receptor (EGFR) transactivation, cell proliferation and keratinocyte differentiation. Cell proliferation was assessed by measuring bromodeoxyuridine incorporation whereas assessment of cell differentiation was based on the expression of filaggrin, cytokeratin 10 (CK10) and involucrin. Results The major proteins phosphorylated, after B₁R stimulation, were of molecular mass 170, 125, 89 and 70 kDa. The 170‐ and 125‐kDa proteins were identified as EGFR and p125^FAK, respectively. Phosphorylation was greatly reduced by GF109203X and by overexposure of keratinocytes to phorbol 12‐myristate 13‐acetate, indicating the participation of protein kinase C. B₁R stimulation did not increase [Ca²⁺]i, but triggered EGFR transactivation, an event that involved phosphorylation of Tyr⁸⁴⁵, Tyr⁹⁹² and Tyr¹⁰⁶⁸ of EGFR. B₁R stimulation did not elicit keratinocyte proliferation, but triggered cell differentiation, visualized as an increase of filaggrin, CK10 and involucrin. Blockade of EGFR tyrosine kinase by AG1478, before B₁R stimulation, produced an additional increase in filaggrin expression. Conclusions The kinin B₁R may contribute to keratinocyte differentiation and migration by triggering specific tyrosine signalling pathways or by interacting with the ErbB receptor family.