Regulation of serine protease inhibitor Kazal type-5 (SPINK5) gene expression in the keratinocytes

Serine protease inhibitor Kazal type-5 (SPINK5) plays a crucial role in deciding the timing of desquamation of the skin. Its gene expression is limited at the very surface of the stratum granulosum (SG), whereas expression of kallikreins (KLKs) encoding proteases is usually found throughout the stratum spinosum and SG. To explore the difference in expression regulation of these proteases/inhibitors, the function of SPINK5 promoter was examined using luciferase assay. Luciferase assay targeting the SPINK5 promoters (nucleotide -676/-532 and -318/-146 from the major transcription start site) showed high intensity in NHEK human keratinocyte. These two sites had neither common cis-elements nor GATA3 element but electrophoretic mobility shift assay showed similar retardation bands. Moreover, DNA footprinting did not display specific protected bands. Thus, we could not identify cis-element(s) that controlled these elements. Differentiation induced by high Ca2+ medium failed to alter their luciferase activities. Transfection of GATA3 expressing vector significantly but slightly increased them and that of vector expressing its dominant negative form decreased. Although GATA3 is reportedly important for inhibition of proliferation and induction of differentiation of keratinocytes, its effect on SPINK5 expression was indirect and GATA3 alone was insufficient for final differentiation of keratinocytes where full SPINK5 expression was observed.