TGF-β Induced CTGF Expression in Human Lung Epithelial Cells through ERK, ADAM17, RSK1, and C/EBPβ Pathways

Abstract

Background: Lung epithelial cells play critical roles in idiopathic pulmonary fibrosis. Methods: In the present study, we investigated whether transforming growth factor-β (TGF-β)-induced expression of connective tissue growth factor (CTGF) was regulated by the extracellular signal-regulated kinase (ERK)/a disintegrin and metalloproteinase 17 (ADAM17)/ribosomal S6 kinases 1 (RSK1)/CCAAT/enhancer-binding protein β (C/EBPβ) signaling pathway in human lung epithelial cells (A549). Results: Our results revealed that TGF-β-induced CTGF expression was weakened by ADAM17 small interfering RNA (ADAM17 siRNA), TNF-α processing inhibitor-0 (TAPI-0, an ADAM17 inhibitor), U0126 (an ERK inhibitor), RSK1 siRNA, and C/EBPβ siRNA. TGF-β-induced ERK phosphorylation as well as ADAM17 phosphorylation was attenuated by U0126. The TGF-β-induced increase in RSK1 phosphorylation was inhibited by TAPI-0 and U0126. TGF-β-induced C/EBPβ phosphorylation was weakened by U0126, ADAM17 siRNA, and RSK1 siRNA. In addition, TGF-β increased the recruitment of C/EBPβ to the CTGF promoter. Furthermore, TGF-β enhanced fibronectin (FN), an epithelial–mesenchymal transition (EMT) marker, and CTGF mRNA levels and reduced E-cadherin mRNA levels. Moreover, TGF-β-stimulated FN protein expression was reduced by ADAM17 siRNA and CTGF siRNA. Conclusion: The results suggested that TGF-β induces CTGF expression through the ERK/ADAM17/RSK1/C/EBPβ signaling pathway. Moreover, ADAM17 and CTGF participate in TGF-β-induced FN expression in human lung epithelial cells.

ADAM 17 and Epithelial-to-Mesenchymal Transition: The Evolving Story and Its Link to Fibrosis and Cancer

“…These investigations start from several lines of evidence of the role of RSK1 and protein kinase C (PKC) in the phosphorylation of C/EBPβ, a transcription factor that participates in the modulation of pro-inflammatory protein expression [ 108 , 109 ]. Moreover, CTGF participates in the mechanism leading to TGF-induced FN expression in human lung epithelial cells [ 110 ]; in an experimental model represented by TGF-β-induced renal fibrosis in mice, this mechanism was inhibited, blocking MEK activity and so attenuating CTGF expression [ 111 ]; however, it remains unclear as to whether RSK1 and C/EBPβ are involved in TGF-β-induced CTGF expression in human lung epithelial cells and what is ADAM17’s role in EMT activation in the lung. Starting from the results obtained from Blom et al [ 104 ], suggesting that CTGF acts as a modulator of TGF-β-dependent fibrogenesis and EMT activation in lung epithelial cells [ 104 ], studies have since progressed; it was demonstrated that TGF-β-induced CTGF expression in human lung epithelial cells provides the participation of ERK, ADAM17, RSK1 and C/EBPβ [ 110 ], and both ADAM17 and CTGF seem to mediate TGF-β-induced FN expression [ 110 ].…”

“…Moreover, CTGF participates in the mechanism leading to TGF-induced FN expression in human lung epithelial cells [ 110 ]; in an experimental model represented by TGF-β-induced renal fibrosis in mice, this mechanism was inhibited, blocking MEK activity and so attenuating CTGF expression [ 111 ]; however, it remains unclear as to whether RSK1 and C/EBPβ are involved in TGF-β-induced CTGF expression in human lung epithelial cells and what is ADAM17’s role in EMT activation in the lung. Starting from the results obtained from Blom et al [ 104 ], suggesting that CTGF acts as a modulator of TGF-β-dependent fibrogenesis and EMT activation in lung epithelial cells [ 104 ], studies have since progressed; it was demonstrated that TGF-β-induced CTGF expression in human lung epithelial cells provides the participation of ERK, ADAM17, RSK1 and C/EBPβ [ 110 ], and both ADAM17 and CTGF seem to mediate TGF-β-induced FN expression [ 110 ]. It is clear now the involvement of ADAM17 in the TGF-β-induced expression of CTGF and EMT in the lung; in fact, ADAM17 gene silencing reduced TGF-β-induced CTGF and FN expression in human alveolar basal epithelial cell line [ 110 ].…”

“…Starting from the results obtained from Blom et al [ 104 ], suggesting that CTGF acts as a modulator of TGF-β-dependent fibrogenesis and EMT activation in lung epithelial cells [ 104 ], studies have since progressed; it was demonstrated that TGF-β-induced CTGF expression in human lung epithelial cells provides the participation of ERK, ADAM17, RSK1 and C/EBPβ [ 110 ], and both ADAM17 and CTGF seem to mediate TGF-β-induced FN expression [ 110 ]. It is clear now the involvement of ADAM17 in the TGF-β-induced expression of CTGF and EMT in the lung; in fact, ADAM17 gene silencing reduced TGF-β-induced CTGF and FN expression in human alveolar basal epithelial cell line [ 110 ]. Furthermore, through the use of CTGF gene knockdown, a reduced TGF-β-induced FN expression was observed, confirming the correlated importance of ADAM17 and CTGF in TGF-β-induced FN expression in human lung epithelial cells [ 110 ].…”

“…It is clear now the involvement of ADAM17 in the TGF-β-induced expression of CTGF and EMT in the lung; in fact, ADAM17 gene silencing reduced TGF-β-induced CTGF and FN expression in human alveolar basal epithelial cell line [ 110 ]. Furthermore, through the use of CTGF gene knockdown, a reduced TGF-β-induced FN expression was observed, confirming the correlated importance of ADAM17 and CTGF in TGF-β-induced FN expression in human lung epithelial cells [ 110 ]. Further clarifications on the molecular mechanisms involved in IPF fibrosis emerged through studying the ERK pathway activation that seems to regulate the expression of pro-fibrotic proteins in IPF such as osteopontin [ 112 ].…”

ADAM17 Aggravates the Inflammatory Response by Modulating Microglia Polarization Through the TGF-β1/Smad Pathway Following Experimental Traumatic Brain Injury

“…However, the role and underlying mechanism of ADAM17 in the regulation of in ammatory responses after TBI remain unclear. Considering that ADAM17 is an important regulatory factor of the TGF-β pathway [27,28], it may be closely related to microglia polarization and the neuroin ammatory response. Therefore, the aim of the present study was to determine whether ADAM17 can in uence the M1/M2 polarization of microglia and the neuroin ammatory response mediated by the TGF-β pathway in the pathological process after TBI.…”