Sphingosylphosphorylcholine is an activator of transglutaminase activity in human keratinocytes

Kazuhiko Higuchi,* Makoto Kawashima,* Yutaka Takagi,† Hidehiko Kondo,† Yukihiro Yada,† Yoshiaki Ichikawa,† and Genji Imokawa1,†

Abstract

Abstract We characterize functional roles of a newly discovered chemical, sphingosylphosphorylcholine (SPC), in the epidermis by elucidating the biological effect of SPC on human keratinocytes in culture. The intracellular calcium level of human keratinocytes was increased by incubation with SPC, but not with sphingosine (SS) or sphingomyelin(SM). The addition of SPC, sphingosine 1-phosphate (SSP), or SS to human keratinocytes at 10 mM concentrations also
significantly suppressed DNA synthesis, and SPC, but not SSP, or SS increased the activities of membrane-bound and
soluble transglutaminases (TGases). Reverse transcription polymerase chain reaction (RT-PCR) of TGase transcripts revealed that SPC treatment at 10 mM concentrations increased the expression of TGase 1 mRNA. The increased activity of soluble TGase was accompanied by the concomitant activation of cathepsin D as revealed by the increased
ratio of mature active form to inactive intermediate form of the protease. Pretreatment of human keratinocytes with
pepstatin, a protease inhibitor, blocked the increase in soluble TGase activity induced by treatment with SPC. Consistently, SPC treatment at 1–10 µM concentrations stimulated the cornified envelope formation. These findings
suggest that SPC plays an important role in the altered keratinization process of epidermis in skin diseases with high
expression of sphingomyelin deacylase, such as atopic dermatitis.—Higuchi, K., M. Kawashima, Y. Takagi, H. Kondo, Y.
Yada, Y. Ichikawa, and G. Imokawa. Sphingosylphosphorylcholine is an activator of transglutaminase activity in human
keratinocytes. J. Lipid Res. 2001. 42: 1562–1570.

Supplementary key words sphingomyelin deacylase • atopic dermatitis • sphingolipid • ceramide