UVB-induced apoptosis in normal human keratinocytes: role of the erbB receptor family.

Exposure of human keratinocytes to ultraviolet B (UVB) light leads to the activation of a variety of cell-surface receptors; however, the biologic consequences of these activated receptors are still unclear. It was previously reported that inhibition of cellular tyrosine kinase activity suppressed UVB-dependent effects in human skin. We confirmed that the same suppression of UVB-induced apoptosis occurs in normal human keratinocytes grown in culture. Furthermore, we sought to determine the role of erbB receptor tyrosine kinases in human keratinocytes following UVB irradiation. Using a specific inhibitor of the erbB family of tyrosine kinase receptors, DAPH, we investigated the effects of UVB-dependent activation of these receptors on keratinocyte biology. The addition of DAPH to keratinocytes resulted in the concentration-dependent protection of UVB-induced apoptosis. The protection from apoptosis was not due to the induction of keratinocyte differentiation, the loss of keratinocyte viability, or inhibition of the proliferative potential of keratinocytes by DAPH. The effect of DAPH on apoptosis was specific for UVB as it had no effect on bleomycin-induced apoptosis. Furthermore, the inhibition of UVB-induced apoptosis could also be observed using neutralizing antibodies to either erbB1 or erbB2. Finally, we demonstrated that DAPH could also inhibit UVB-induced apoptosis in an epidermal organotypic model system. These studies suggest an important role for the erbB receptors in UVB-induced apoptosis of human keratinocytes.

Inhibition of erbB receptor family members protects HaCaT keratinocytes from ultraviolet-B-induced apoptosis.

In the human epidermis, the cells most at risk for the development of cancer due to sunlight exposure are the keratinocytes. In animal models, ultraviolet-B is a complete carcinogen, capable of inducing and promoting the development of malignant cells. A key element of ultraviolet-B-induced carcinogenesis is the ability of ultraviolet-B to induce the expression of a number of cellular proteins and activate growth factor receptor tyrosine kinases, including the erbB receptor family. Keratinocytes express the erbB1 (also called EGF-R, HER1), the erbB2 (also known as neu or HER2), and the erbB3 (HER3) subtypes. In general, activation of the erbB receptor family leads to a cellular proliferative response. In certain instances, however, activation of an erbB receptor can induce differentiation, cell cycle arrest, and even apoptosis. The inhibition of tyrosine kinase activity in rodent models and human skin has been shown to inhibit some ultraviolet-B response pathways. We have shown that the inhibition of erbB receptors, by both pharmaceutical and immunologic means, will inhibit ultraviolet-B-induced apoptosis in the HaCaT human keratinocyte cell line. This inhibition was specific for the erbB receptor family and specific for ultraviolet-B-induced apoptosis. These results suggest that, in certain instances, ultraviolet-B-induced apoptotic signaling requires erbB family receptor activity.