Two keratins MW 50,000 and 56,000 are synthesized by psoriatic epidermis.

The keratin polypeptide composition of uninvolved psoriatic epidermis is the same as normal epidermis. In contrast, involved epidermis from psoriasis contains significant amounts of two keratin polypeptides, molecular weight (MW) 56 and 50 kilodaltons (KD). Involved epidermis contains decreased amounts of keratins MW 69, 66.5 and 65.2 KD. Slices of involved psoriatic epidermis incorporate [35S]methionine into all the keratins including those of MW 56 and 50 KD. Unexpectedly, we found that [35S]methionine is incorporated into 56 and 50 KD keratins in uninvolved epidermis even though these keratins are not abundant enough to be seen in Coomassie stained gels. The two-dimensional patterns of iodinated tryptic peptide digests of keratin MW 50 KD from uninvolved, involved and normal epidermis are identical. We conclude that keratins of MW 56 KD and 50 KD are abundant in involved psoriatic epidermis. They are not present in normal or uninvolved psoriatic epidermis, but are rapidly synthesized when normal epidermis (neonatal foreskin) or uninvolved psoriatic epidermis are removed and placed in organ culture. The two keratins may be markers of increased cell proliferation or injury.