betekintés - Molecular Biology - # Role of STAG3 in post-transcriptional regulation of gene expression during pluripotency exit in mouse embryonic stem cells

STAG3 Regulates Pluripotency Exit and Cell Fate Decisions through Post-transcriptional mRNA Control in the Cytoplasm

Q: How does STAG3 mechanistically regulate the structure and function of cytoplasmic condensates like P-bodies and the centrosome to control post-transcriptional gene expression?

STAG3 plays a crucial role in the regulation of cytoplasmic condensates, particularly P-bodies and the centrosome, which are essential for post-transcriptional gene expression. Mechanistically, STAG3 is localized predominantly in the cytoplasm, where it interacts with various RNA-binding proteins (RBPs) and components of the RNA-induced silencing complex (RISC). This localization allows STAG3 to influence the stability and localization of mRNAs within these condensates. In P-bodies, STAG3 is thought to interact with proteins such as DDX6 and TNRC6C, which are known to be involved in mRNA degradation and silencing. By stabilizing these RBPs, STAG3 may facilitate the sequestration of specific mRNAs, thereby repressing their translation. The destabilization of TNRC6C upon STAG3 knockdown indicates that STAG3 is vital for maintaining the integrity of P-bodies, which serve as sites for mRNA storage and degradation. At the centrosome, STAG3's interaction with microtubule-associated proteins suggests a role in organizing the cytoskeleton, which is critical for the transport of mRNAs to specific cellular locations. The centrosome has been identified as a site for localized translation, and STAG3's presence there may help regulate the translation of mRNAs that are essential for cell fate decisions. The destabilization of centrosome structure upon STAG3 knockdown further supports its role in maintaining the functional integrity of these cytoplasmic condensates, thereby controlling the spatial and temporal aspects of gene expression.

Q: What are the full spectrum of mRNA targets that are post-transcriptionally regulated by STAG3, and how do these contribute to the control of cell identity and fate decisions?

The full spectrum of mRNA targets regulated by STAG3 includes key pluripotency factors and germ cell markers, such as Dppa3 and Nanog. STAG3's post-transcriptional regulation of these mRNAs is critical for maintaining cell identity and facilitating transitions between different cell states, such as from pluripotency to differentiation. For instance, STAG3 negatively regulates Dppa3 translation, which is essential for the exit from pluripotency in mouse embryonic stem cells (mESCs). The upregulation of Dppa3 upon STAG3 knockdown leads to a hyper-ESC state, indicating that STAG3 is necessary for proper differentiation signaling. Similarly, the increase in Nanog protein levels upon STAG3 knockdown suggests that STAG3 also plays a role in the regulation of other pluripotency-associated mRNAs. Moreover, STAG3's interaction with RBPs that bind to specific mRNA sequences, such as AU-rich elements, allows it to selectively regulate mRNAs involved in cytoskeletal organization and intracellular transport. This selective regulation is crucial for maintaining the dynamic nature of cell identity, as it enables cells to respond to differentiation cues while preserving essential pluripotent characteristics.

Q: Given that STAG3 is upregulated in various cancers, how might its role in post-transcriptional regulation of gene expression be deregulated in the context of cancer and contribute to disease progression?

In the context of cancer, the upregulation of STAG3 may lead to the deregulation of post-transcriptional gene expression, contributing to tumorigenesis and disease progression. The mechanisms by which STAG3 may become dysregulated include alterations in its expression levels, changes in its interaction with RBPs, and modifications to its localization within the cell. In cancer cells, the increased levels of STAG3 could enhance the stability and translation of mRNAs that promote cell proliferation and survival, while simultaneously repressing mRNAs that are involved in differentiation and apoptosis. This shift in mRNA regulation could result in a more aggressive cancer phenotype, characterized by increased migratory and invasive capabilities. Furthermore, the destabilization of key proteins involved in mRNA regulation, such as TNRC6C, upon STAG3 knockdown suggests that STAG3 may play a role in maintaining the integrity of P-bodies and other cytoplasmic condensates that are crucial for mRNA silencing. In cancer, the disruption of these regulatory mechanisms could lead to the accumulation of oncogenic mRNAs and the loss of tumor suppressor mRNAs, thereby promoting uncontrolled cell growth and metastasis. Overall, the role of STAG3 in post-transcriptional regulation highlights its potential as a therapeutic target in cancer, where restoring normal STAG3 function could help re-establish proper gene expression patterns and inhibit tumor progression.

Alapfogalmak

STAG3, a cohesin regulator traditionally associated with meiosis, plays a key role in post-transcriptional control of gene expression in the cytoplasm of mouse embryonic stem cells to facilitate their exit from the pluripotent state.

Kivonat

The content describes a novel, non-canonical function of the STAG3 protein in mouse embryonic stem cells (mESCs). STAG3 is primarily localized to the cytoplasm in mESCs, where it interacts with an array of RNA-binding proteins (RBPs) and is enriched at the centrosome.

Key findings:

STAG3 is expressed in mESCs and its levels increase during differentiation towards epiblast-like cells (EpiLCs) and primordial germ cell-like cells (PGCLCs).
Knockdown of Stag3 in mESCs leads to a "hyper-ESC" state, with increased levels of the pluripotency regulator DPPA3 despite reduced Dppa3 mRNA levels.
This disconnect between mRNA and protein levels for key regulators like DPPA3 and NANOG suggests a post-transcriptional regulatory role for STAG3.
STAG3 interacts with RBPs involved in mRNA localization, stability and translation, including components of the RISC complex and P-bodies.
Loss of STAG3 destabilizes the centrosome structure and the P-body protein TNRC6C, leading to derepression of P-body localized mRNAs like Dppa3.
The data supports a model where STAG3 collaborates with RBPs to control post-transcriptional gene expression and facilitate the transition from pluripotency in mESCs.

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biorxiv.org

Statisztikák

STAG3 mRNA levels are 3.9-fold and 2.4-fold lower than STAG1 and STAG2, respectively, in naïve mESCs.
Stag3 knockdown leads to a 62% reduction in Stag3 mRNA and a 58% reduction in STAG3 protein in mESCs.
Stag3 knockdown increases the proportion of undifferentiated AP+ colonies by 41% compared to controls.
Stag3 knockdown reduces Dppa3 mRNA by 51% but increases DPPA3 protein levels.
Inhibition of translation by cycloheximide rescues the reduction in Dppa3 mRNA upon Stag3 knockdown.
Stag3 knockdown reduces TNRC6C protein levels by 47% in the cytoplasmic fraction of mESCs.

Idézetek

"STAG3 collaborates with RNA-binding proteins (RBPs) and specific target mRNAs to control post-transcriptional gene expression and facilitate the transition from pluripotency in mESCs."
"STAG3 may repress the translation of specific mRNAs in P-bodies, either those transported along the cytoskeleton or stationary ones at the centrosomes."

Főbb Kivonatok

STAG3 promotes exit from pluripotency through post-transcriptional mRNA regulation in the cytoplasm

by Weeks,S., Pe... : www.biorxiv.org 05-31-2024

https://www.biorxiv.org/content/10.1101/2024.05.31.595485v1

Mélyebb kérdések

How does STAG3 mechanistically regulate the structure and function of cytoplasmic condensates like P-bodies and the centrosome to control post-transcriptional gene expression?

STAG3 plays a crucial role in the regulation of cytoplasmic condensates, particularly P-bodies and the centrosome, which are essential for post-transcriptional gene expression. Mechanistically, STAG3 is localized predominantly in the cytoplasm, where it interacts with various RNA-binding proteins (RBPs) and components of the RNA-induced silencing complex (RISC). This localization allows STAG3 to influence the stability and localization of mRNAs within these condensates.
In P-bodies, STAG3 is thought to interact with proteins such as DDX6 and TNRC6C, which are known to be involved in mRNA degradation and silencing. By stabilizing these RBPs, STAG3 may facilitate the sequestration of specific mRNAs, thereby repressing their translation. The destabilization of TNRC6C upon STAG3 knockdown indicates that STAG3 is vital for maintaining the integrity of P-bodies, which serve as sites for mRNA storage and degradation.
At the centrosome, STAG3's interaction with microtubule-associated proteins suggests a role in organizing the cytoskeleton, which is critical for the transport of mRNAs to specific cellular locations. The centrosome has been identified as a site for localized translation, and STAG3's presence there may help regulate the translation of mRNAs that are essential for cell fate decisions. The destabilization of centrosome structure upon STAG3 knockdown further supports its role in maintaining the functional integrity of these cytoplasmic condensates, thereby controlling the spatial and temporal aspects of gene expression.

What are the full spectrum of mRNA targets that are post-transcriptionally regulated by STAG3, and how do these contribute to the control of cell identity and fate decisions?

The full spectrum of mRNA targets regulated by STAG3 includes key pluripotency factors and germ cell markers, such as Dppa3 and Nanog. STAG3's post-transcriptional regulation of these mRNAs is critical for maintaining cell identity and facilitating transitions between different cell states, such as from pluripotency to differentiation.
For instance, STAG3 negatively regulates Dppa3 translation, which is essential for the exit from pluripotency in mouse embryonic stem cells (mESCs). The upregulation of Dppa3 upon STAG3 knockdown leads to a hyper-ESC state, indicating that STAG3 is necessary for proper differentiation signaling. Similarly, the increase in Nanog protein levels upon STAG3 knockdown suggests that STAG3 also plays a role in the regulation of other pluripotency-associated mRNAs.
Moreover, STAG3's interaction with RBPs that bind to specific mRNA sequences, such as AU-rich elements, allows it to selectively regulate mRNAs involved in cytoskeletal organization and intracellular transport. This selective regulation is crucial for maintaining the dynamic nature of cell identity, as it enables cells to respond to differentiation cues while preserving essential pluripotent characteristics.

Given that STAG3 is upregulated in various cancers, how might its role in post-transcriptional regulation of gene expression be deregulated in the context of cancer and contribute to disease progression?

In the context of cancer, the upregulation of STAG3 may lead to the deregulation of post-transcriptional gene expression, contributing to tumorigenesis and disease progression. The mechanisms by which STAG3 may become dysregulated include alterations in its expression levels, changes in its interaction with RBPs, and modifications to its localization within the cell.
In cancer cells, the increased levels of STAG3 could enhance the stability and translation of mRNAs that promote cell proliferation and survival, while simultaneously repressing mRNAs that are involved in differentiation and apoptosis. This shift in mRNA regulation could result in a more aggressive cancer phenotype, characterized by increased migratory and invasive capabilities.
Furthermore, the destabilization of key proteins involved in mRNA regulation, such as TNRC6C, upon STAG3 knockdown suggests that STAG3 may play a role in maintaining the integrity of P-bodies and other cytoplasmic condensates that are crucial for mRNA silencing. In cancer, the disruption of these regulatory mechanisms could lead to the accumulation of oncogenic mRNAs and the loss of tumor suppressor mRNAs, thereby promoting uncontrolled cell growth and metastasis.
Overall, the role of STAG3 in post-transcriptional regulation highlights its potential as a therapeutic target in cancer, where restoring normal STAG3 function could help re-establish proper gene expression patterns and inhibit tumor progression.