Ryuta Muromoto

1. Introduction The primary function of the epidermis is to construct an indispensable barrier between the organism and the desiccated terrestrial environment preventing invasion of external stimuli and loss of water from the body. As summarized in a previous study, many factors are involved in epidermal barrier function [1] [2]. Lipids, which are stored in lamellar bodies in the stratum granulosum and secreted into the extracellular space, are crucial for epidermal barrier function [3].

Psoriasis is an inflammatory skin condition that affects some 125 million people worldwide. It is characterized by itchy, scaly skin plaques. The exact cause of psoriasis is unclear. But mounting evidence implicates the immune system in the overproduction of cell-signalling molecules called cytokines, which stimulate skin cells called keratinocytes to express genes that maintain an inflammatory microenvironment.

Signal transducer and activator of transcription 3 (STAT3) is involved in cell proliferation, differentiation, and cell survival during immune responses, hematopoiesis, neurogenesis, and other biological processes. STAT3 activity is regulated by a variety of mechanisms, including phosphorylation and nuclear translocation. To clarify the molecular mechanisms underlying the regulation of STAT3 activity, we performed yeast two-hybrid screening.