Redistribution of LRIG proteins in psoriasis.

The human leucine-rich repeats and immunoglobulin-like domains (LRIG) family is composed of three members, LRIG1, -2, and -3, which are all expressed in human skin. LRIG1 negatively regulates growth factor signaling and is involved in the regulation of epidermal stem cell quiescence. Ablation of Lrig1 in mice results in psoriasiform epidermal hyperplasia. Hence, the LRIG proteins may be important for epidermal homeostasis and in psoriasis. Therefore, we analyzed the LRIG mRNA levels and the cellular and subcellular distribution of LRIG proteins in normal and psoriatic skin. The mRNA levels of LRIG1, -2, and -3 were not significantly different in psoriatic epidermis compared to clinically normal epidermis from the same patient. Immunohistochemistry showed that all three LRIG proteins were expressed in unique and specific patterns both in normal and psoriatic skin. Intriguingly, in psoriatic epidermis, the LRIG protein expression patterns were altered compared to normal skin. These results indicate that the LRIG proteins may have a role in epidermal homeostasis and psoriasis.