Interleukin-33 (IL-33), the most recently identified member of the IL-1 family, induces synthesis of T Helper 2 (Th2)-type cytokines via its heterodimeric ST2/IL-1RAcP receptor. Th2-type cytokines play an important role in fibrosis; thus, we investigated the role of IL-33 in liver fibrosis. IL-33, ST2 and IL-1RAcP gene expression was analysed in mouse and human normal (n= 6) and fibrotic livers (n= 28), and in human hepatocellular carcinoma (HCC; n= 22), using real-time PCR. IL-33 protein was detected in normal and fibrotic liver sections and in isolated liver cells using Western blotting and immunolocalization approaches. Our results showed that IL-33 and ST2 mRNA was overproduced in mouse and human fibrotic livers, but not in human HCC. IL-33 expression correlated with ST2 expression and also with collagen expression in fibrotic livers. The major sources of IL-33 in normal liver from both mice and human beings are the liver sinusoidal endothelial cells and, in fibrotic liver, the activated hepatic stellate cells (HSC). Moreover, IL-33 expression was increased in cultured HSC when stimulated by pro-inflammatory cytokines. In conclusion, IL-33 is strongly associated with fibrosis in chronic liver injury and activated HSC are a source of IL-33.

Transforming growth factor-β (TGF-β) regulates a wide variety of biological processes through two types of Ser/Thr transmembrane receptors: the TGF-β type I receptor and the TGF-β type II receptor (TβRII). Upon ligand binding, TGF-β type I receptor activated by TβRII propagates signals to Smad proteins, which mediate the activation of TGF-β target genes. In this study, we identify ADAM12 (a disintegrin and metalloproteinase 12) as a component of the TGF-β signaling pathway that acts through association with TβRII. We found that ADAM12 functions by a mechanism independent of its protease activity to facilitate the activation of TGF-β signaling, including the phosphorylation of Smad2, association of Smad2 with Smad4, and transcriptional activation. Furthermore, ADAM12 induces the accumulation of TβRII in early endosomal vesicles and stabilizes the TβRII protein presumably by suppressing the association of TβRII with Smad7. These results define ADAM12 as a new partner of TβRII that facilitates its trafficking to early endosomes in which activation of the Smad pathway is initiated.

Reepithelialization during cutaneous wound healing involves numerous signals that result in basal keratinocyte activation, spreading, and migration, all linked to a loosening of cell-cell adhesion structures. The transcription factor Slug is required for this process, and EGF treatment of human keratinocytes induced activating phosphorylation of Erk5 that coincides with slug transcription. Accordingly, ectopic activation of Erk5 led to increased Slug mRNA levels and faster wound healing, whereas keratinocyte migration was totally blocked by Erk5 pathway inhibition. Expression of a shRNA specific for Erk5 strongly diminished Erk5 levels in keratinocytes and significantly decreased their motility response to EGF, along with induction of Slug expression. These Erk5-deprived keratinocytes showed an altered, more compact morphology, along with disruption of desmosome organization. Accordingly, they displayed an altered ability to form cell aggregates. These results implicate a novel EGFR/Erk5/Slug pathway in the control of cytoskeleton organization and cell motility in keratinocytes treated with EGF.