p-CREB-1 promotes hepatic fibrosis through the transactivation of transforming growth factor-β1 expression in rats

Abstract

Abstract. Phosphorylated cAMP-responsive element binding protein-1 (p-CREB-1) is an important transcription factor which has been reported to be implicated in fibrogenesis. However, the association between p-CREB-1 and transforming growth factor-β1 (TGF-β1)-mediated liver fibrogenesis remains poorly understood. In the present study, exogenous TGF-β1 recombinant protein was used to activate hepatic stellate cells (HSCs), and we established a rat model of tetrachloromethane (CCl 4 )-induced liver fibrosis. Loss-and gain-of-function studies were performed to examine the role of p-CREB-1 in liver fibrogenesis, and the detailed mechanism responsible for these effects was further explored using chromatin immunoprecipitation and luciferase reporter gene assays. We found that p-CREB-1 expression was significantly upregulated in a rat model of hepatic fibrosis. We also demonstrated that p-CREB-1 increased TGF-β1 expression and auto-induction in HSCs, through directly binding to the CRE site within the TGF-β1 promoter in order to enhance its transcriptional activity. Moreover, lentivirus-mediated CREB-1 overexpression promoted hepatic fibrogenesis in rats. These findings suggest that p-CREB-1 may function as a potent profibrogenic factor through the transactivation of TGF-β1 expression in liver fibrosis. IntroductionHepatic fibrosis, characterized by the excessive production and deposition of the extracellular matrix (ECM), is a common pathologic change observed in the progression of various chronic liver diseases to cirrhosis (1-3). Transforming growth factor-β1 (TGF-β1), the most potent profibrogenic cytokine currently known, stimulates the activation and transformation of hepatic stellate cells (HSCs) into myofibroblasts producing abnormal and abundant ECM (4,5). It has been reported that TGF-β1 binds to TGF-β type II receptors on the cell surface, and then recruits type I receptors; as a consequence, the type II receptor kinase phosphorylates the type I receptors and intracellular signal molecules such as Smads. Phosphorylated (p-)Smad2 and/or p-Smad3 form heteroligomers with Smad4, which translocate into the nucleus to control the ECM gene transcription (6-7). On the contrary, blocking TGF-β1 signaling may inhibit collagen production and promote the degradation of collagen (8,9). The roles of TGF-β1 in HSCs activation and liver fibrosis have been intensively studied; however, the transcriptional regulation of TGF-β1 remains poorly understood.Cyclic adenosine 3' ,5'-monophosphate (cAMP)-responsive element (CRE) binding protein-1 (CREB-1), a eukaryotic transcription factor, binds to CRE sites in the promoters of various cytokines to widely regulate gene transcription (10,11). The role of CREB-1 in fibrogenesis remains controversial. Several studies have reported that CREB-1 exerts anti-fibrotic effects, such as in myocardial fibrosis and pulmonary fibrosis (12,13). On the contrary, CREB-1 facilitated high glucose induced renal tubulointerstitial fibrosis in diabetic nephropathy (14). Currently, there limited research r...

Conophylline suppresses pancreatic cancer desmoplasia and cancer‐promoting cytokines produced by cancer‐associated fibroblasts

“…46 In contrast, another report showed that CREB promoted hepatic fibrosis through the transactivation of TGFβ expression in rats. 47 Thus, there is a possibility that CREB is a key factor involved in the activity of CnP. We confirmed that TGFβ expression of CAF was decreased by CnP treatment ( Figure S6).…”

“…Moreover, CREB has previously been shown to regulate inflammatory responses by directly regulating gene transcription of proinflammatory genes, such as IL‐6 and TNF‐α, and CREB silencing has been shown to reduce the levels of IL‐6, IL‐8, and CCL2 in malignant mesothelioma cells . In contrast, another report showed that CREB promoted hepatic fibrosis through the transactivation of TGF‐β expression in rats . Thus, there is a possibility that CREB is a key factor involved in the activity of CnP.…”

Autophagy induces transforming growth factor‐β‐dependent epithelial‐mesenchymal transition in hepatocarcinoma cells through cAMP response element binding signalling

“…Our previous study showed that autophagy promotes invasion of hepatocarcinoma cells by inducing TGF‐β1‐dependent EMT . Here, we provided further evidence showing that autophagy‐induced TGF‐β1 expression in hepatocarcinoma cells by activating cAMP/PKA/CREB signalling, consistent with previous reports demonstrating that p‐CREB can induce TGF‐β gene expression both in normal cells and in cancer cells by directly binding to the CRE site in the TGF‐β gene promoter . This autophagy‐induced activation of cAMP/PKA/CREB signalling was dependent on degradation of PDE4A based on the fact that inhibition of autophagy preserved PDE4A expression but inactivated cAMP/PKA/CREB signalling; however, inhibition of PDE4A‐activated cAMP/PKA/CREB signalling in autophagy‐deficient hepatocarcinoma cells, indicating a negative regulatory mechanism of cAMP/PKA/CREB signalling triggered by autophagy in hepatocarcinoma cells under starvation.…”

“…p‐CREB was reported to induce TGF‐β1 expression by binding to the CRE site in the TGF‐β1 gene promoter . Since activation of cAMP/PKA/CREB signalling was significantly promoted by autophagy (Figure ), and autophagy also induced TGF‐β1 expression in hepatocarcinoma cells under starvation, we further investigated the role of cAMP/PKA/CREB signalling in autophagy‐induced TGF‐β1 expression in HepG2 and BEL7402 cells.…”

“…Activation of the CREB signalling pathway and phosphorylation of CREB were shown to fulfill numerous cellular functions ranging from cell proliferation and the cell cycle to cell differentiation and cytokine production by binding of phosphorylated‐CREB to the cAMP response element (CRE) in target genes and promoting their transcription . A CRE site has been identified in the TGF‐β gene promoter, and p‐CREB induces TGF‐β expression in both normal cells and cancer cells by directly binding to the TGF‐β gene promoter, which contributes to tissue fibrosis or tumour progression …”