Erlotinib impairs epidermal tight junction and barrier integrity by inhibiting EGFR and Src and affects maturation of cell-cell junctions in human and mouse keratinocytes.

Erlotinib, an epidermal growth factor receptor (EGFR) inhibitor, is widely used in cancer therapy but frequently causes cutaneous adverse effects that suggest impairment of the epidermal barrier. To better understand the underlying mechanisms, we examined how erlotinib affects barrier integrity, with a focus on tight junctions (TJs) and their relation with the actin cytoskeleton. Using human and mouse ex vivo epidermis as well as cultured keratinocytes, we assessed junctional assembly and stability under pharmacological inhibition of EGFR and Src. Erlotinib treatment disrupted the epithelial barrier, as demonstrated by enhanced biotin tracer penetration and a marked reduction in transepithelial electrical resistance. In line with functional impairment, erlotinib reduced EGFR and Src activity disturbing maturation of junctions, as evidenced by discontinuous claudin-1 and ZO-1 localization. Furthermore, erlotinib induced a loss of the apically localized tension-sensitive conformation of α-catenin in the stratum granulosum and in cultured keratinocytes. This was accompanied by disorganization of cortical actin and increased presence of stress fibers, in parallel with elevated activation of RhoA and phosphorylation of MLC2. Inhibition of Src with PP2 led to similar effects on barrier integrity. However, this detrimental outcome could be rescued by EGF treatment. Together, these findings indicate that erlotinib impairs epidermal barrier function by affecting junctional maturation via disrupted α-catenin membrane distribution, and ultimately, TJ stability involving intracellular contraction and tension. Thus, strategies focused on targeting tension‑related mechanisms downstream of EGFR/Src might help prevent or alleviate the cutaneous toxicities associated with EGFR inhibitory therapies.