Identification of human hornerin and its expression in regenerating and psoriatic skin.

We previously isolated a new member of the fused-type S100 protein family (hornerin) from the mouse (Makino, T., Takaishi, M., Morohashi, M., and Huh, N.-h. (2001) J. Biol. Chem. 276, 47445-47452). Mouse hornerin shares structural features, expression profiles, and intracellular localization with profilaggrin, indicating possible involvement of hornerin in cornification. In this study, we identified and partially characterized a human ortholog of mouse hornerin. The human hornerin gene was mapped between trichohyalin and filaggrin on chromosome 1q21.3, the region being completely syntenic with the counterpart of the mouse. The deduced amino acid sequence of 2850 residues shows typical structural features of "fused-type" S100 protein family members. Mature transcripts and protein from human hornerin were not detected in normal stratified epithelium, including the trunk epidermis, tongue, and esophagus. After screening of various normal and pathological human tissues, we found that human hornerin was expressed in psoriatic skin. Hornerin protein was present in the keratinizing region, although at a lower level and in fewer cells compared with filaggrin. Mature transcripts and protein from hornerin were also detected in regenerating human skin after wounding. Hornerin mRNA was induced 5 days after wounding. The mRNA level remained almost constant until 15 days and declined at 30 days after wounding. Hornerin protein was detected in the proximal epidermis (but not in the distal epidermis) at 15 days after wounding. These results indicate that hornerin has a function similar to but distinct from that of filaggrin in cornification.