Epidermal proteins. I. Differential extraction and quantitative polyacrylamide gel-electrophoretic analysis of basal spinous-cell proteins of neonatal mouse epidermis

The study of keratinocyte proteins and their changes in different physiological, experimental, and pathological states has been facilitated and stimulated by the development of high-resolution polyacrylamide gel electrophoretic (PAGE) techniques. We describe a differential extraction system that separates the keratinocyte proteins into four major groups which are further quantitatively analyzed by PAGE: (1) cytoplasmic-soluble proteins, (2) nonionic-detergentsoluble proteins consisting of membrane-associated protein, (3) salt-dissociated proteins mainly consisting of histones, and ribosomal and keratohyaline granule proteins, and (4) the keratins (and other intermediate-filament-associated proteins), which are further separated into disulfide-stabilized keratins and keratins that do not require reducing agents in order to dissolve in sodium dodecyl sulfate (SDS) or urea. This extraction system was applied to neonatal mouse epidermal cell preparations that consisted mainly (60%-85%) of basal cells and also of some spinous cells (10%-30%). The SDS-PAGE patterns obtained by spectrophotometric scanning were graphically compared and integrated using an IBM personal computer. The protein bands in each extract were identified by their apparent molecular weights and were quantitated as a percentage of the total in each extract and in micrograms per 15×10⁶ cells. Some protein peaks were provisionally identified as actin, the core histones H2A, H2B, H3, and H4, ribosomal proteins, and six keratins. This study serves as the foundation for the quantitative description of molecular changes which occur during keratinocyte differentiation and for the comprehensive identification of epidermal proteins.