Mutant loricrin is not crosslinked into the cornified cell envelope but istranslocated into the nucleus in loricrin keratoderma

Loricrin is a major constituent of the epidermal cornified cell envelope. W e have recently identified heterozygous loricrin gene mutations in two domi nantly inherited skin diseases, the ichthyotic variant of Vohwinkel syndrom e and progressive symmetric erythrokeratoderma, collectively termed loricri n keratoderma. In order to see whether the mutant loricrin molecules predic ted by DNA sequencing are expressed in vivo and to define their pathologic effects, we raised antibodies against synthetic peptides corresponding to t he mutated sequences of loricrin. Immunoblotting of horny cell extracts fro m loricrin keratoderma patients showed specific bands for mutant loricrin. Immunohistochemistry of loricrin keratoderma skin biopsies showed positive immunoreactivity to the mutant loricrin antibodies in the nuclei of differe ntiated epidermal keratinocytes. The immunostaining was localized to the nu cleoli of the lower granular cell layer. As keratinocyte differentiation pr ogressed the immunoreactivity moved gradually into the nucleoplasm leaving nucleoli mostly nonimmunoreactive. No substantial staining was observed alo ng the cornified cell envelope. This study confirmed that mutant loricrin w as expressed in the loricrin keratoderma skin. Mutant loricrin, as a domina nt negative disrupter, is not likely to affect cornified cell envelope cros slinking directly, but seems to interfere with nuclear/nucleolar functions of differentiating keratinocytes. In addition, detection of the mutant lori crin in scraped horny layer could provide a simple noninvasive screening te st for loricrin keratoderma.