Mutant Loricrin is Not Crosslinked into the Cornified Cell Envelope but is Translocated into the Nucleus in Loricrin Keratoderma

Abstract

Loricrin is a major constituent of the epidermal cornified cell envelope. We have recently identified heterozygous loricrin gene mutations in two dominantly inherited skin diseases, the ichthyotic variant of Vohwinkel syndrome and progressive symmetric erythrokeratoderma, collectively termed loricrin keratoderma. In order to see whether the mutant loricrin molecules predicted by DNA sequencing are expressed in vivo and to define their pathologic effects, we raised antibodies against synthetic peptides corresponding to the mutated sequences of loricrin. Immunoblotting of horny cell extracts from 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 differentiated epidermal keratinocytes. The immunostaining was localized to the nucleoli of the lower granular cell layer. As keratinocyte differentiation progressed the immunoreactivity moved gradually into the nucleoplasm leaving nucleoli mostly nonimmunoreactive. No substantial staining was observed along the cornified cell envelope. This study confirmed that mutant loricrin was expressed in the loricrin keratoderma skin. Mutant loricrin, as a dominant negative disrupter, is not likely to affect cornified cell envelope crosslinking directly, but seems to interfere with nuclear/nucleolar functions of differentiating keratinocytes. In addition, detection of the mutant loricrin in scraped horny layer could provide a simple noninvasive screening test for loricrin keratoderma. J Invest Dermatol 115:1088-1094 2000

Suppressing AP1 Factor Signaling in the Suprabasal Epidermis Produces a Keratoderma Phenotype

“…These mutations result in synthesis of an extended form of loricrin that includes a nuclear localization signal. Instead of being incorporated into the cornified envelope, the mutant loricrin translocates into the nucleus where it produces changes that are not well characterized (Ishida-Yamamoto et al , 1999; Ishida-Yamamoto et al , 2000; Ishida-Yamamoto et al , 1998b). …”

TRPV3 mutants causing Olmsted Syndrome induce impaired cell adhesion and nonfunctional lysosomes

“…26 Notably, LOR gene codes for loricrin, the main component of the cornified cell envelop present iN-terminally differentiated epidermis, and it is also associated with inherited skin diseases, namely with Vohwinkel's Syndrome and progressive symmetric erythrokeratoderma. 27 However, specific screening studies have failed to detect any mutations in LOR gene in OS patients. 17 No mutations have been detected in 3 other genes namely KRT1 (Keratin 1), GJB2 (Gap junction protein b 2) and SLURP1 (Secreted Ly-6/uPAR-related protein 1); which are otherwise involved in other skin-related problems.…”

Activation of Vascular Endothelial Growth Factor Receptor 2 in a Cellular Model of Loricrin Keratoderma

“…Suga et al (34) insisted that it conferred a gain of function to the system. However, Ishida-Yamamoto et al (21) thought that mutant loricrin worked as a dominant-negative disrupter. Mutant loricrin gains nuclear localization signals and is transported to the nucleoli.…”

“…An anti-RhoA antibody (Santa Cruz Biotechnology) was used as an irrelevant antibody for the ChIP assay. A peptide with the C-terminal 18 amino acids of mutant loricrin plus cysteine at the N terminus (CPGYHGGEGVGGVFQGHRWA) was synthesized (21). This peptide was covalently coupled to keyhole limpet hemocyanin through the sulfhydryl group of the N-terminal cysteine with the bifunctional cross-linker m-maleimidobenzoyl-N-hydroxysuccinimide ester and used to immunize a rabbit.…”