SMAD4 Feedback Activates the Canonical TGF-β Family Signaling Pathways

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.

A regulatory network controlling ovarian granulosa cell death

“…According to our previous 5′RACE assay [ 17 ], the full-length Yorkshire sows TGFBR2 5′-UTR is 188 bp, which is completely consistent with Duroc pigs (Fig. 1A, B ).…”

“…In addition to TGF-β1, several modifying factors, including casitas B-lineage lymphoma (Cbl) [ 14 ], ubiquitin-specific peptidase 9 X-linked (USP9X) [ 15 ], asparagine-linked glycosylation 10 (ALG10) [ 8 ], and programmed death-ligand 1 (PD-L1) [ 16 ], also directly activate or maintain levels of activated TGFBR2 protein through neddylation, ubiquitination, glycosylation modifications, and lysosomal degradation. TGFBR2 promoter binding, transcription factors including SMAD4 [ 17 ] and GABPA [ 9 ] activate TGFBR2 transcription, whereas MYOCD [ 18 ] inhibits TGFBR2 transcription. At the post-transcriptional level, several miRNAs have been reported to directly interact with the 3′ untranslated region (UTR) of their mRNAs to decrease TGFBR2 levels [ 19 , 20 ].…”

“…In sow granulosa cells (GCs), we previously demonstrated that TGFBR2 is a vital anti-apoptotic factor that is downregulated by miRNAs that bind to its 3′-UTR [ 12 , 15 ]. TGFBR2 can also be induced by binding SMAD4 to its promoter [ 17 ], and its protein levels are maintained by the deubiquitinase activity of USP9X [ 15 ] in sow GCs. In this study, using the 5′-UTR as the target region, we investigated the regulatory mechanism of TGFBR2 expression in sow GCs.…”

MEIS1 Is a Common Transcription Repressor of the miR-23a and NORHA Axis in Granulosa Cells

“…Moreover, these genes are not independent of each other and usually form regulatory axes, signaling pathways, and even regulatory networks to work together [ 1 , 2 ]. Interestingly, in addition to co-expression and the same functions, genes of the same regulatory axis or signaling pathway are sometimes directly regulated by the same regulators [ 3 , 4 ]. The C-X-C chemokine ligand 13 (CXCL13) and C-X-C chemokine receptor type 5 (CXCR5) signaling axis, for instance, play an essential role in B cell recruitment and tertiary lymphoid structure formation, which is transcriptionally activated by a common transcription factor RelA, a subunit of the NF-κB family in breast tumors [ 5 ].…”

TGF‐β1 regulates the lncRNA transcriptome of ovarian granulosa cells in a transcription activity‐dependent manner

“…In the canonical TGF‐β signaling pathway, the extracellular ligands (e.g., TGF‐β1) with signals specifically bind to and activate type II and type I receptors (e.g., TGFBR2 and TGFBR1) in the cell membrane, which further phosphorylate activates R‐SMADs (e.g., SMAD2/3) and shuttles into the nucleus by forming a heteromeric complex with SMAD4 (the only co‐SMAD). In the nucleus, the R‐SMADs/SMAD4 transcription complex with signals regulates the transcription of downstream target genes (coding and noncoding) with or without the help of coregulators depending on the cell type and biological contexts 17–19 …”