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Co-transcriptional nuclear actin dynamics.

Percipalle P - Nucleus (2012)

Bottom Line: This high degree of promiscuity in the spectrum of protein-to-protein interactions correlates well with the conformational plasticity of actin and the ability to undergo regulated changes in its polymerization states.Several of the factors involved in controlling head-to-tail actin polymerization have been shown to be in the nucleus where they seem to regulate gene activity.By focusing on the multiple tasks performed by actin and actin-binding proteins, possible models of how actin dynamics controls the different phases of the RNA polymerase II transcription cycle are being identified.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Molecular Biology, Karolinska Institute, Stockholm, Sweden. piergiorgio.percipalle@ki.se

ABSTRACT
Actin is a key player for nuclear structure and function regulating both chromosome organization and gene activity. In the cell nucleus actin interacts with many different proteins. Among these proteins several studies have identified classical nuclear factors involved in chromatin structure and function, transcription and RNA processing as well as proteins that are normally involved in controlling the actin cytoskeleton. These discoveries have raised the possibility that nuclear actin performs its multi task activities through tight interactions with different sets of proteins. This high degree of promiscuity in the spectrum of protein-to-protein interactions correlates well with the conformational plasticity of actin and the ability to undergo regulated changes in its polymerization states. Several of the factors involved in controlling head-to-tail actin polymerization have been shown to be in the nucleus where they seem to regulate gene activity. By focusing on the multiple tasks performed by actin and actin-binding proteins, possible models of how actin dynamics controls the different phases of the RNA polymerase II transcription cycle are being identified.

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Figure 4. The actin nucleocytoplasmic transport cycle. Actin is actively imported into the nucleus in complex with cofilin. Ran-dependent nuclear import requires the import factor importin 9 which interacts with actin-associated cofilin. In the nucleus actin is excluded from heterochromatin and it is mostly found to be coupled to euchromatin and consistently, actin import supports transcription. From the cell nucleus actin is exported in complex with profilin. Active nuclear export of the profilin-actin complex is regulated by exportin 6 which specifically targets profilin. By controlling the nucleocytoplasmic shuttling of actin, cofilin and profilin tightly regulate transcription and gene activity.
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Figure 4: Figure 4. The actin nucleocytoplasmic transport cycle. Actin is actively imported into the nucleus in complex with cofilin. Ran-dependent nuclear import requires the import factor importin 9 which interacts with actin-associated cofilin. In the nucleus actin is excluded from heterochromatin and it is mostly found to be coupled to euchromatin and consistently, actin import supports transcription. From the cell nucleus actin is exported in complex with profilin. Active nuclear export of the profilin-actin complex is regulated by exportin 6 which specifically targets profilin. By controlling the nucleocytoplasmic shuttling of actin, cofilin and profilin tightly regulate transcription and gene activity.

Mentions: Here, the most intriguing question is whether such an exquisite regulatory mechanism is conserved in the cell nucleus and whether it could also be occurring along active genes. Profilin and cofilin are known to be relatively abundant in the nucleus.76,77 Profilin and cofilin shuttle between cytoplasm and nucleus. Cofilin serves as adaptor for active Ran-dependent nuclear import of the cofilactin complex via importin 9, whereas profilin is an adaptor for the nuclear export of actin through exportin 6.78,79 Above all, nuclear import of actin supports transcription (Fig. 4).79 Therefore profilin and cofilin are also important for gene activity. In C. tentans polytene chromosomes, profilin localizes to active transcription units and appears to be required for ongoing transcription, since a transcriptional block with actinomycin D or DRB leads to a global release of profilin from the transcription sites.73 These findings confirm and extend the importance of profilin in mammalian gene expression.77,80 In the nucleus, profilin was found to partly co-localize with snRNP-core proteins, Cajal bodies and gems,77,80 which altogether suggest a complex role(s) for profilin at different layers, in both transcription and pre-mRNA processing.


Co-transcriptional nuclear actin dynamics.

Percipalle P - Nucleus (2012)

Figure 4. The actin nucleocytoplasmic transport cycle. Actin is actively imported into the nucleus in complex with cofilin. Ran-dependent nuclear import requires the import factor importin 9 which interacts with actin-associated cofilin. In the nucleus actin is excluded from heterochromatin and it is mostly found to be coupled to euchromatin and consistently, actin import supports transcription. From the cell nucleus actin is exported in complex with profilin. Active nuclear export of the profilin-actin complex is regulated by exportin 6 which specifically targets profilin. By controlling the nucleocytoplasmic shuttling of actin, cofilin and profilin tightly regulate transcription and gene activity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585027&req=5

Figure 4: Figure 4. The actin nucleocytoplasmic transport cycle. Actin is actively imported into the nucleus in complex with cofilin. Ran-dependent nuclear import requires the import factor importin 9 which interacts with actin-associated cofilin. In the nucleus actin is excluded from heterochromatin and it is mostly found to be coupled to euchromatin and consistently, actin import supports transcription. From the cell nucleus actin is exported in complex with profilin. Active nuclear export of the profilin-actin complex is regulated by exportin 6 which specifically targets profilin. By controlling the nucleocytoplasmic shuttling of actin, cofilin and profilin tightly regulate transcription and gene activity.
Mentions: Here, the most intriguing question is whether such an exquisite regulatory mechanism is conserved in the cell nucleus and whether it could also be occurring along active genes. Profilin and cofilin are known to be relatively abundant in the nucleus.76,77 Profilin and cofilin shuttle between cytoplasm and nucleus. Cofilin serves as adaptor for active Ran-dependent nuclear import of the cofilactin complex via importin 9, whereas profilin is an adaptor for the nuclear export of actin through exportin 6.78,79 Above all, nuclear import of actin supports transcription (Fig. 4).79 Therefore profilin and cofilin are also important for gene activity. In C. tentans polytene chromosomes, profilin localizes to active transcription units and appears to be required for ongoing transcription, since a transcriptional block with actinomycin D or DRB leads to a global release of profilin from the transcription sites.73 These findings confirm and extend the importance of profilin in mammalian gene expression.77,80 In the nucleus, profilin was found to partly co-localize with snRNP-core proteins, Cajal bodies and gems,77,80 which altogether suggest a complex role(s) for profilin at different layers, in both transcription and pre-mRNA processing.

Bottom Line: This high degree of promiscuity in the spectrum of protein-to-protein interactions correlates well with the conformational plasticity of actin and the ability to undergo regulated changes in its polymerization states.Several of the factors involved in controlling head-to-tail actin polymerization have been shown to be in the nucleus where they seem to regulate gene activity.By focusing on the multiple tasks performed by actin and actin-binding proteins, possible models of how actin dynamics controls the different phases of the RNA polymerase II transcription cycle are being identified.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Molecular Biology, Karolinska Institute, Stockholm, Sweden. piergiorgio.percipalle@ki.se

ABSTRACT
Actin is a key player for nuclear structure and function regulating both chromosome organization and gene activity. In the cell nucleus actin interacts with many different proteins. Among these proteins several studies have identified classical nuclear factors involved in chromatin structure and function, transcription and RNA processing as well as proteins that are normally involved in controlling the actin cytoskeleton. These discoveries have raised the possibility that nuclear actin performs its multi task activities through tight interactions with different sets of proteins. This high degree of promiscuity in the spectrum of protein-to-protein interactions correlates well with the conformational plasticity of actin and the ability to undergo regulated changes in its polymerization states. Several of the factors involved in controlling head-to-tail actin polymerization have been shown to be in the nucleus where they seem to regulate gene activity. By focusing on the multiple tasks performed by actin and actin-binding proteins, possible models of how actin dynamics controls the different phases of the RNA polymerase II transcription cycle are being identified.

Show MeSH