SMAD4 Feedback Activates the Canonical TGF-β Family Signaling Pathways.

Lu Liu,Liu Yang,Xing Du,Qifa Li,Qiqi Li

doi:10.3390/ijms221810024

Abstract

TGF-β family signaling pathways, including TGF-β and BMP pathways, are widely involved in the regulation of health and diseases through downstream SMADs, which are also regulated by multiple validated mechanisms, such as genetic regulation, epigenetic regulation, and feedback regulation. However, it is still unclear whether R-SMADs or Co-SMAD can feedback regulate the TGF-β family signaling pathways in granulosa cells (GCs). In this study, we report a novel mechanism underlying the feedback regulation of TGF-β family signaling pathways, i.e., SMAD4, the only Co-SMAD, positive feedback activates the TGF-β family signaling pathways in GCs with a basal level of TGF-β ligands by interacting with the core promoters of its upstream receptors. Mechanistically, SMAD4 acts as a transcription factor, and feedback activates the transcription of its upstream receptors, including ACVR1B, BMPR2, and TGFBR2, of the canonical TGF-β signaling pathways by interacting with three coactivators (c-JUN, CREB1, and SP1), respectively. Notably, three different interaction modes between SMAD4 and coactivators were identified in SMAD4-mediated feedback regulation of upstream receptors through reciprocal ChIP assays. Our findings in the present study indicate for the first time that SMAD4 feedback activates the canonical TGF-β family signaling pathways in GCs, which improves and expands the regulatory mechanism, especially the feedback regulation modes of TGF-β family signaling pathways in ovarian GCs.

Highlights

Our findings revealed that SMAD4 acts as a transcription factor, and feedback induces the transcription of upstream receptors of the transforming growth factor-β (TGF-β) family signaling pathways by interacting with three coactivators (CREB1, c-JUN, and SP1) in different modes
We showed that ACVR1B, BMPR2, and TGFBR2 are three potential direct targets of SMAD4 and further indicated that SMAD4 can feedback activate the whole TGF-β family signaling pathways by inducing crucial receptors in a specific cell type: porcine granulosa cells (GCs)
We reanalyzed the effects of SMAD4 knockdown on the transcriptome of porcine GCs and identified that three crucial TGF-β family signaling pathway upstream receptors (ACVR1B, BMPR2, and TGFBR2) were positive-feedback regulated by SMAD4 in porcine GCs

Summary

Introduction

The transforming growth factor-β (TGF-β) superfamily is a large group of phylogenetically conserved secreted cytokines in eukaryotes, which contains more than 30 members, including TGF-βs, activins, inhibins, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs) [1]. Members of the TGF-β superfamily are widely expressed in various tissues and cells, which play critical roles in the regulation of multiple crucial biological processes associated with health and disease, mainly by activating or inhibiting the TGF-β family signaling pathways [2]. The TGF-β family signaling pathway can be divided into two branches, i.e., TGF-β and BMP signaling pathways, which both signal in the order of ligands, receptors (including type II and type I receptors), receptor-regulated SMADs (R-SMADs: SMAD2/3 for the TGF-β signaling pathway, and SMAD1/5/8 for the BMP signaling pathway), and the only common mediator SMAD (Co-SMAD: SMAD4), which shuttles into the nucleus to regulate the transcription of target genes [3]

Methods

Results

Discussion

Conclusion