Phorbol ester-induced expression of airway squamous cell differentiation marker, SPRR1B, is regulated by protein kinase C delta/Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway

The transcriptional induction of SPRR1B by phorbol 12-myristate 13-acetate (PMA) is mainly mediated by the first -152-base pair 5'-flanking region con taining two functional AP-1 sites. In this study, we have analyzed the sign aling pathways that mediate the induction in tracheobronchial epithelial ce lls. PKC inhibitor ablated PMA-stimulated expression of endogenous SPRR1B a nd reporter gene expression driven by SPRR1B promoter. PKC activator promot ed the transcription. The dominant negative protein kinase C delta (dn-PKC delta) and rottlerin (PKC delta inhibitor) completely suppressed PMA-stimul ated promoter activity, dn-Ras or dn-MEKK1 inhibited PMA-stimulated promote r activity, while their corresponding constitutively active mutants augment ed it. dn-c-Raf-1 did not have any effect on reporter gene expression. Sinc e MEKK1 activates multiple parallel pathways, we examined involvement of JN K/SAPK, p38, and MKK1 in promoter regulation. Go-expression of the dominant negative forms of MKK4, MKK7, JNK/SAPK, MKK3, MKK6, or p38 alpha did not s uppress PMA-stimulated reporter gene expression. However, MKK1 inhibitors U O126 and PD98095 suppressed gene expression. Consistent with this, expressi on of dn-MKK1 strongly suppressed PMA-stimulated promoter activity, while t he constitutively active MKK1 augmented it. However, MKK1-mediated inductio n of SPRR1B probably does not depend on extracellular signal-regulated kina ses 1 and 2, suggesting the requirement of another kinase(s). dnc-Jun mutan ts abolished PMA-stimulated expression supporting an important role for AP- l proteins in SPRR1B expression. Together, these results suggest that a PKC delta/Ras/MEKK1/MKK1-dependent/AP-1 pathway regulates the PMA-inducible ex pression of the SPRR1B in tracheobronchial epithelial cells.