We detected elastin mRNA in cultured normal human keratinocytes by RNase protection assay. The content of elastin mRNA was estimated at approximately one-twentieth of that of cultured skin fibroblasts. Tropoelastin polypeptide with a molecular weight of 68 kDa was detected in the preparation of culture medium of normal human keratinocytes by western blot assays using anti-tropoelastin antibody. Immunohistochemical studies also demonstrated positive staining in cultured normal human keratinocytes as well as in skin fibroblasts. The expression of elastin by normal human keratinocytes was found to reach a maximum level at the quiescent phase of keratinocyte growth. When normal human keratinocytes were cultured on tropoelastin-coated dishes, their growth potential was greatly suppressed compared with other matrix protein-coated dishes. These results suggest that cultured normal human keratinocytes can actively synthesize elastin and that keratinocyte elastin may act as a growth-regulator for keratinocytes.

Late-onset focal dermal elastosis has recently been described as new clinical entity characterized by pseudoxanthoma elasticum-like eruptions and an accumulation of normal-appearing elastic fibres in the dermis. Elastin and collagen contents of the skin of 2 patients were 2- and 1.4-fold higher than in the skin of controls, respectively. A focal accumulation of elastin but not of fibrillin-1 was observed by immunohistochemical staining. The levels of type I and III collagen and elastin mRNAs isolated from cultured patient fibroblasts were elevated 2-3-fold compared with control fibroblasts. There was no significant change in the excretion of elastin peptides in the urine of patients and controls. These results suggest that the focal accumulation of elastic fibres in the patient skin may be related to overexpression of elastin rather than to altered degradation of elastin.