The expression of the c-myc, c-fos, c-jun, c-erbB, and c-Ha-ras protooncogenes was compared by Northern blot analysis of total RNA extracted from keratome biopsies of normal skin and psoriatic plaques. Isolation of intact RNA from frozen tissue required careful attention to technique during the early stages of extraction. Densitometric analysis revealed 1.5- to 2.5-fold elevations of c-myc transcript levels in lesional psoriatic relative to normal epidermis. Similar increases in cyclophilin and lipocortin II transcripts were also observed and may reflect characteristic differences in RNA preparations from normal and psoriatic epidermis. C-myc, c-jun, c-erbB, c-fos, and c-Ha-ras transcript levels were not significantly increased in lesional psoriatic epidermis when protooncogene mRNA levels were normalized to those of the cyclophilin or lipocortin genes. In contrast, transforming growth factor-alpha (TGF-alpha) transcripts were significantly increased (10- to 20-fold) with or without prior normalization. C-myc, c-fos, and c-jun transcripts were significantly induced over in vivo levels 2-4 h after organ culture of normal or psoriatic keratome biopsies, demonstrating that these genes can be highly expressed in the context of tissue injury. Our results suggest that overexpression of these protooncogenes per se is not central to the pathogenesis of psoriatic epidermal hyperplasia.
Epidermis Gene Expression Regulation