The role of epidermal growth factor in skin diseases

Receptor recognition by histidine 16 of human epidermal growth factor via hydrogen-bond donor/acceptor interactions

Human epidermal growth factor (hEGF) and human transforming growth factor alpha (hTGFalpha) are prototypical of structurally related polypeptide mitogens which interact with the epidermal growth factor receptor (EGFR). Several determinants of receptor recognition that specify function have been proposed on the basis of structural criteria. This study evaluates the role of one such candidate, H16 of hEGF, by site-specific mutagenesis. When assayed for receptor tyrosine kinase stimulation using (Glu4,Tyr1)n as the exogenous substrate in vitro, the relative agonist activities of position 16 mutants range from 14-263% of wild-type hEGF. The rank order of potency was found to correlate with the relative receptor binding affinities of the mutants, which range from 7-272% of wild-type, as determined by radioreceptor competition assays. The mitogenic activity of the H16 mutants is similar to that of wild-type hEGF as determined by clonogenic assays using rat tracheal epithelial cells. While the colony forming efficiencies do not reflect significant differences in growth rate or survival characteristics in the presence of the hEGF variants, it is reduced to 1.6% in control cultures which lack EGF in the medium. The results show that H16 of hEGF, although not essential for mitogenic activity, optimizes receptor recognition by hydrogen-bond donor/acceptor interactions and may share this feature with H18 of hTGFalpha.

Pachydermoperiostosis: study of epidermal growth factor and steroid receptors

Pachydermoperiostosis is a rare osteo-cutaneous disease characterized by hypertrophy of bones and surrounding soft tissues. The cutaneous manifestations include coarsening of facial features, cutis verticis gyrata, digital clubbing, hyperhidrosis and seborrhoea. The pathogenetic mechanism of the disease is still debated, and proposed aetiological factors include genetic influences, anomalies in fibroblast activity, or alteration in peripheral blood flow. We studied a patient with the incomplete form of pachydermoperiostosis, assessing epidermal growth factor receptor (EGF-R) and sex hormone steroid receptors (SR) in the affected skin, and also evaluating the urinary excretion of EGF. The results showed high levels of nuclear steroid receptors, increased cytosolic oestrogen receptors, and no detectable progesterone and androgen cytosolic receptors. EGF-R was also undetectable, and the urinary excretion of EGF was elevated. These findings suggest that the increased tissue sensitivity to circulating sex-steroids could induce enhanced tissue EGF/transforming growth factor alpha (TGF-alpha) production and utilization. The SR-EGF-R system could therefore be involved in determining hypertrophy of the affected tissues.

Biology of basal cell carcinoma (Part II)

Host-tumor relationships involve several factors that can enhance or suppress neoplastic growth. This second part of a review of basal cell carcinoma biology examines the role that hormones, cytokines, local and systemic immunity, congenital and genetic syndromes, and environmental factors play in the development of this neoplasm. Theories of etiology and pathogenesis are discussed, and transplantation and cell culture techniques used to study this cancer are explored. Valuable second-line therapies for treatment of multiple tumors are reviewed, and important areas of present and future research are emphasized.

Lipid modulators of epidermal proliferation and differentiation

The importance of lipids within the skin as components of the permeability barrier has been appreciated for quite some time. However, the more recent work reviewed here suggests numerous alternative bioactive functions for lipid molecules within the skin and other tissues. The precise roles of lipids in epidermal proliferation and differentiation have only begun to be studied and are far from being defined.

Immunolocalization of epidermal growth factor receptors in normal developing human skin

The embryogenesis of normal human skin is a complex process involving multiple cell types and developmentally regulated growth factors. The immunohistochemical localization of epidermal growth factor receptors (EGF-R) was studied in human fetal skin because this receptor modulates all known actions of EGF and TGF-alpha. EGF-R are present in developing skin as early as the 42nd day of gestation. Immunoreactive EGF-R are present in keratinocytes, endothelial, and skeletal muscle cells. In contrast to normal adult human skin in which the EGF-R are primarily restricted to the basal and immediately suprabasal keratinocytes, the fetal epidermis showed a persistent expression of EGF-R in all cell layers. The absence of EGF-R on the outer, apical surface of periderm cells that are exposed to amniotic fluid was unexpected and may reflect down-regulation of EGF-R by EGF/TGF-alpha or related fetal growth factors present in amniotic fluid. The complex regulation of EGF-R in embryonic hair follicles and sebaceous glands indicates an active and perhaps regulatory role for EGF/TGF-alpha in the development and function of pilosebaceous glands as well as mammalian skin in general.