May act as a soluble regulator of keratinocyte differentiation. May play an important role in embryonic skin morphogenesis. Highly expressed in skin and detected at lower levels in thymus. In skin, found exclusively in lamellar granules of granular keratinocytes and in the intracellular space of the stratum corneum. Also highly expressed in oral mucosa, tongue, esophagus, and stomach, and at much lower levels in bladder and uterus. Not detected in gastrointestinal mucosa. Up-regulated in situ in psoriatic skin (at protein level).