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Keratoacanthoma (KA) is a variant of cutaneous squamous cell carcinoma (SCC) known for rapid growth and potential for involution. Little is known about the basis for the rapid growth because of the dearth of model systems. We hypothesized that amphiregulin (AR), a keratinocyte autocrine growth factor, had a significant role. Using immunohistochemistry, we compared 21 KA, 6 conventional SCC, and 6 basal cell carcinomas (BCC) for AR expression. All KA were positive for AR, the majority with strong immunoreactivity. The SCC were positive (5 of 6), with generally weak staining; no BCC were positive. We developed laboratory model systems to study AR overexpression in keratinocytes and its role in the pathogenesis of KA. A retroviral transduction strategy was used to overexpress AR in the HaCaT keratinocyte-like cell line. The AR overexpressing cells (HaCaT-AR) displayed autonomous proliferation in serum-free media when compared with controls (HaCaT-NIE). To develop an in vivo model, xenografts of HaCaT-AR and HaCaT-NIE were grown on SCID mice. The HaCaT-NIE cells formed thin tumors resembling conventional SCC. The HaCaT-AR cells formed rapidly growing tumors with AR expression similar to KA. HaCaT-AR cells may represent a new system for the further evaluation of KA.

Although originally conceived as a basis for malignant cell growth, autocrine signaling networks are currently known to be activated during tissue repair and with in vitro cultivation. In human epidermal keratinocytes, activation of the epidermal growth factor receptor by cognate ligands mediates the majority of the autonomous replicative capacity of these cells and is necessary to inhibit differentiation and apoptosis. The importance of heparin-binding growth factors in activation of this receptor was first suggested by the strong anti-proliferative effects of soluble heparin-like molecules on keratinocyte growth. This and related evidence led to the identification of amphiregulin as a major autocrine factor for keratinocytes. The binding of amphiregulin and its homolog, heparin-binding epidermal growth factor-like growth factor, to the receptor is potentially amplified by autoinduction and cross-signaling through epidermal growth factor-related polypeptides and by transmodulation of other ErbB-family receptors (HER-2, -3, -4) in cells expressing these receptors. Heparan sulfate proteoglycans and the tetraspanin family of membrane-associated proteins appear to act as cofactors in amphiregulin-driven mitogenesis mediated by the epidermal growth factor receptor, but amphiregulin's immunolocalization to keratinocyte nuclei and to filopodia may indicate other potentially novel effects. Following from the observation that amphiregulin is overexpressed in lesional psoriatic epidermis, the importance of amphiregulin in hyperproliferative skin diseases has been further supported by recent studies of the targeted expression of a transgene encoding keratin 14 promoter-driven human amphiregulin to the basal epidermis of mice. Founder transgenic mice displayed a morphologic and microscopic cutaneous phenotype that shares characteristics with psoriasis. Pharmacologic regulation of amphiregulin's expression and receptor signaling may eventually prove to be an effective strategy in the treatment of hyperproliferative skin diseases.

We determined the concentration of cytosol estrogen receptors in the postnatal, developing right and left cerebral cortices of Long-Evans male or female rats 2 to 3, 7 to 8, 14 to 15, and 25 to 26 days of age. Under anesthesia, the rats were gonadectomized and 24 h later they were killed by decapitation, and the dorsal right and left cerebral cortices were separated from the underlying white matter and placed on ice. Sephadex LH-20 gel filtration chromatography was used to dissociate the majority of alpha-fetoprotein-bound [3H]estradiol while leaving the receptor [3H]estradiol complex intact. The correction for the residual nonreceptor binding, including alpha-fetoprotein, was made using parallel incubation containing unlabeled diethylstilbesterol. The amount of residual nonreceptor binding was subtracted from [3H]estradiol-bound protein to calculate high-affinity estradiol binding receptors. The results showed that in both sexes, estrogen receptor concentration was highest at postnatal days 2 to 3 in both the right and the left cerebral cortex and then decreased until 25 days of age. In the female, the right cerebral cortex, at postnatal day 2 to 3, had a higher estrogen receptor concentration than the left cortex (P less than 0.02). In the male, the left cortex had a higher cytoplasmic estrogen receptor concentration (P less than 0.02) than the right. Considering the reported growth-inhibiting effects of estrogen on the cerebral cortex, the results indicated that one determinant of cerebral dominance in both sexes may be the differential exposure to estrogen, in the case of the male testosterone converted to estrogen, during a critical period of development.