LGI3 promotes human keratinocyte differentiation via the Akt pathway.

Leucine-rich repeat LGI family member 3 (LGI3), a member of the LGI family, is a secreted protein that is expressed not only in the brain and adipose tissues, but also in various skin cells. We previously reported that LGI3 was secreted after exposure to ultraviolet B and promoted the migration of HaCaT human keratinocytes. In the present study, we investigated whether LGI3 influences the differentiation of keratinocytes. The results show that the expression of involucrin, a keratinocyte differentiation marker, was reduced in tissue from LGI3-knockout mice. Those results indicate that LGI3 plays an important role in keratinocyte differentiation. Therefore, we treated HaCaT cells with LGI3 to examine its effect on keratinocyte differentiation. Protein levels of various differentiation markers were enhanced by treatment with LGI3. Furthermore, expression of differentiation markers was inhibited when keratinocytes were transfected with an siRNA for LGI3. LGI3 strongly activated Akt, whereas it had no apparent effect on extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, or the c-Jun N-terminal kinase. A specific inhibitor of phosphoinositide 3-kinase, LY294002, reduced LGI3-induced expression of differentiation markers in HaCaT cells. Taken together, these results suggest that LGI3 promotes keratinocyte differentiation and could be used as a therapeutic agent to recover skin barrier function in epidermal barrier disruption.