Activation of erbB2 and c-src in phorbol ester-treated mouse epidermis: possible role in mouse skin tumor promotion

Abstract

In recent work we showed that the EGF receptor (EGFr) was activated in tumor promoter treated mouse epidermis (Cell Growth & Dierentiation, 6: 1447 ± 1455. In the present study, we have investigated the possible role of other erbB family members in the process of tumor promotion. Both erbB2 and erbB3, but not erbB4, were expressed in cultured mouse keratinocytes and in mouse epidermis in vivo. In cultured mouse keratinocytes, EGF stimulated rapid tyrosine phosphorylation of erbB2 followed by a time-dependent degradation of erbB2 protein. Furthermore, an increase in erbB2 : EGFr heterodimer formation was also induced by EGF. In contrast to the results with erbB2, EGF did not induce tyrosine phosphorylation, the degradation of erbB3, or erbB3 : EGFr heterodimer formation in cultured keratinocytes. Further analyses revealed that c-src kinase activity was dramatically elevated in cultured mouse keratinocytes exposed to EGF. In mouse epidermis following multiple treatments with 12-O-tetradecanoylphorbol-13-acetate (TPA), the phosphotyrosine content of erbB2 was signi®cantly elevated in a dose-dependent manner. Concomittantly, erbB2 : EGFr heterodimer formation and c-src kinase activity were also elevated in TPA-treated epidermis. Structure-activity relationships with several phorbol ester analogs showed that the elevated phosphorylation of erbB2 in mouse epidermis followed closely with tumor promoting ability. Activation of erbB2 and c-src kinase were also observed in the epidermis of TGFa transgenic mice where expression of human TGFa was targeted to basal keratinocytes with the human K14 promoter. Collectively, the current data suggest that the activation of erbB2 in phorbol ester treated skin can be explained solely by a mechanism involving elevation of EGFr ligands and activation of the EGFr. In addition, activation of c-src may be an important downstream eector in mouse keratinocytes both in vivo and in vitro, following activation of the EGFr, erbB2, or both.

Constitutive expression of erbB2 in epidermis of transgenic mice results in epidermal hyperproliferation and spontaneous skin tumor development

“…We were not able to detect erbB4 in the epidermis of either transgenic or nontransgenic mice (data not shown) which is consistent with our earlier ®ndings (Xian et al, 1997). EGFr and erbB2 proteins were expressed primarily in the basal cell layer, hair follicles, and in the epithelial cells of the sebaceous glands in both transgenic (Figure 3b,d) and nontransgenic mice (Figure 3a,c).…”

“…These mice are relatively resistant to two-stage carcinogenesis when initiated with DMBA followed by promotion with 12-0-tetradecanoylphorbol-13-acetate (TPA) (J Jorcano, personal communication). Recently, we reported that both EGFr and erbB2 were activated and that there was an increase in the formation of erbB2:EGFr heterodimers in EGF-stimulated mouse keratinocytes, TPA-treated mouse epidermis, and in the epidermis of TGFa transgenic mice in which the expression of human TGFa was targeted to basal keratinocytes using the human keratin 14 (K14) promoter (Xian et al, 1997). These latter results suggested the possibility that erbB2 may facilitate signaling through the EGFr during early stages of mouse skin carcinogenesis (i.e.…”

Epidermal growth factor receptor dimerization status determines skin toxicity to HER-kinase targeted therapies

“…However, their technique of choice, coimmunoprecipitation assay, is unsuited to detect homodimers. Another study has reported the absence of EGFR/HER2 heterodimers in mouse keratinocytes using coimmunoprecipitation assays (Xian et al, 1997). Perhaps the reason for such conflicting results has been the absence of a sensitive and quantitative assay to unambiguously measure receptor dimers in vivo.…”

Epidermal Growth Factor as a Biologic Switch in Hair Growth Cycle

“…In order to determine the involvement of other EGFR family members, immunoblotting of ErbB2 and ErbB3 was performed. ErbB4 receptors were excluded since they were not detected in the skin by immunohistochemistry (30). For ErbB2, expression was high in both transgenic and wild type skin at Day 7.…”