CPEB1 or CPEB4 knockdown suppresses the TAK1 and Smad signalings in THP-1 macrophage-like cells and dermal fibroblasts

Post-burn hypertrophic scar (HTS) is a form of excessive dermal fibrosis characterized by cutaneous scarring, which is common in patients following burn injury. Moreover, at least 50% of HTS are accompanied by inflammation. Cytoplasmic polyadenylation element binding (CPEB) proteins are key mRNA-binding proteins that control the translation of several mRNAs. However, their potential roles in treating dermal fibrosis and scarring remain unknown. Therefore, in this study, we aimed to investigate the effects of small interfering RNA (siRNA)-mediated knockdown of CPEB1 or CPEB4 in human THP-1 macrophages and dermal fibroblasts treated with LPS and TGF-β1. We found significantly increased CPEB1 and CPEB4 mRNA and protein levels in LPS-treated THP-1 cells and TGF-β1–treated fibroblasts. CPEB1 and CPEB4 knockdowns suppressed LPS-activated TAK1 signaling cascades by reducing the levels of TNF-α and phosphorylated TAK1, p38, ERK, JNK, and NF-κB-p65 in THP-1 cells. CPEB1 and CPEB4 knockdowns also attenuated TGF-β1-activated Smad-dependent and -independent signaling cascades by reducing the levels of TAK1, p38, ERK, JNK, and phosphorylated Smad 2 and Smad 1/5/8 in fibroblasts. Furthermore, CPEB1 or CPEB4 knockdown markedly decreased the levels of fibrosis markers, including α-SMA, type I collagen, and fibronectin in fibroblasts. Our findings indicate that CPEB1 and CPEB4 are involved in the regulation of the TAK1 and Smad signalings in human macrophages and dermal fibroblasts. These activities may play a role in cutaneous scarring responses.