Cross-linked envelope protein of keratinocytes. It is a keratinocyte protein that first appears in the cell cytosol, but ultimately becomes cross-linked to membrane proteins by transglutaminase. All that results in the formation of an insoluble envelope beneath the plasma membrane (By similarity). Expressed in uterus. During early pregnancy, uterine expression is markedly increased at 1 dpc and 2 dpc, with levels decreasing from 3 dpc onwards. Up-regulated by estrogen in the uterus of ovariectomized animals, with strongly increased expression detected in luminal epithelial cells at 6 and 12 hours after hormone injection. Belongs to the cornifin (SPRR) family.