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Cohesin Acetylation: From Antiestablishment to Establishment
Molecular Cell
Preview Cohesin Acetylation: From Antiestablishment to Establishment Jan-Michael Peters1,* and Venugopal Bhaskara1 1Research Institute of Molecular Pathology, Dr. Bohr-Gasse 7, A-1030 Vienna, Austria *Correspondence: [email protected] DOI 10.1016/j.molcel.2009.03.011
In a recent issue of Molecular Cell, Rowland et al. (2009) report that acetylation of cohesin in S phase transiently counteracts an intrinsic ‘‘antiestablishment’’ activity and, thus, enables establishment of sister chromatid cohesion. When one cell divides into two, all of its nuclear DNA must be faithfully duplicated, and the resulting ‘‘sister’’ DNA molecules must remain connected with each other. Without such sister chromatid cohesion, chromosomes cannot biorient on the spindle later in mitosis or meiosis, nor can they symmetrically segregate into the forming daughter cells. The establishment of sister chromatid cohesion during S phase is, therefore, essential for proper cell division. Cohesion is mediated by cohesins, multisubunit protein complexes that have been proposed to connect sister chromatids by encircling them as molecular rings (reviewed in Peters et al., 2008). Interestingly, the association of cohesin with DNA is required, but not sufficient, for building sister chromatid cohesion in S phase. The identity of other factors that render cohesin ‘‘cohesive’’ during DNA replication has remained one of the greatest enigmas in the areas of cell-cycle and chromosome biology research. For almost a decade, little was known about cohesion establishment in S phase, except that in budding yeast this process depends on the Eco1 acetyltransferase (Skibbens et al., 1999; Toth et al., 1999). Interestingly, early genetic experiments showed that Eco1 is needed only during DNA replication, i.e., when cohesion is established, but not afterwards, thus implying that Eco1 is dispensable for the maintenance of cohesion once it has been established (Skibbens et al., 1999; Toth et al., 1999). It also remained unclear if acetyltransferase activity was essential for Eco1’s function and, if so, what Eco1’s critical substrate might be. Both of these questions were answered by a recent series of key publications (Ben-Shahar et al., 2008;
U¨nal et al., 2008; Rowland et al., 2009). Each group reported that one of cohesin’s subunits, the ATPase Smc3, is the critical target of Eco1. Remarkably, the otherwise essential ECO1 gene becomes dispensable for viability in budding yeast if two lysine residues on Smc3 (K112 and K113), which are acetylated by Eco1, are substituted by glutamine or asparagine residues. These amino acids might mimic the acetylated form of lysine, at least in functional terms. This genetic suppression implies that cohesin acetylation is the only essential function of Eco1 in cohesion establishment. A similar situation might exist in mammalian cells, where the Smc3 subunit of the cohesin complex also becomes acetylated during S phase on two lysine residues that correspond to K112 and K113 in budding yeast (Zhang et al., 2008). Interestingly, U¨nal et al. (2008) observed that Smc3 acetylation occurs only following entry into S phase and depends on chromatin association of cohesin, whereas previous work by Uhlmann and colleagues indicated that Eco1 might travel along DNA together with replication forks (Lengronne et al., 2006). Together, these observations support a model in which cohesin is made cohesive at replication forks by Eco1, which acetylates K112 and K113 on Smc3 (Figure 1). How could two small chemical modifications make cohesin cohesive? A crucial hint to this important question comes from the discovery, made by three independent groups (Ben-Shahar et al., 2008; Rowland et al., 2009; Sutani et al., 2009), that Eco1 also becomes dispensable for viability if either of two other genes, PDS5 or WPL1, are mutated. Pds5 is an essential cohesin-binding protein that is required for cohesion, whereas the function of
Wpl1 in yeast (also known as Rad61) was previously poorly understood. Wpl1 is distantly related to vertebrate Wapl (Kueng et al., 2006), a cohesin-associated protein that is required to remove cohesin from DNA and that forms a complex with Pds5 (Gandhi et al., 2006; Kueng et al., 2006). New results show that Wpl1 also binds to Pds5 and associates with DNA at the same sites as cohesin, lending further support to the idea that Wpl1 represents the budding yeast othologue of Wapl (Ben-Shahar et al., 2008; Rowland et al., 2009; Sutani et al., 2009). Could Wpl1, like its vertebrate counterpart, also have a role in removing cohesin from DNA, and if so, could Smc3 acetylation promote cohesion establishment by protecting cohesin from this dissociation activity? Although this model seemed attractive at first, the phenotypic analysis of yeast cells lacking Wpl1 suggests a different view. In contrast to Wapl-depleted vertebrate cells, which have increased amounts of cohesin on their DNA and ‘‘hypercohesed’’ mitotic chromosomes (Gandhi et al., 2006; Kueng et al., 2006), yeast cells lacking Wpl1 have reduced amounts of cohesin bound to chromatin and display mild cohesion defects (Rowland et al., 2009; Sutani et al., 2009). These results indicate that Wpl1 does not have a major role in removing cohesin from DNA and, therefore, are not consistent with the idea that Smc3 acetylation protects cohesin from dissociation. Instead, Rowland et al. (2009) now propose that Smc3 acetylation might antagonize an ‘‘antiestablishment’’ activity, which normally prevents cohesin from becoming cohesive. Based on the observations that Eco1 becomes dispensable if Wpl1 is deleted, or if Pds5 or the
Molecular Cell 34, April 10, 2009 ª2009 Elsevier Inc. 1
Molecular Cell
Preview
Figure 1. A Speculative Model for the Role of Smc3 Acetylation in Cohesion Establishment during DNA Replication Eco1 might acetylate Smc3 specifically at replication forks (the acetylated lysine residues are indicated as red dots). This modification might promote establishment of cohesion by causing transient opening of the cohesin ring, which according to previous work, could occur via separation of the hinge dimerization domains of Smc1 and Smc3 (reviewed in Peters et al., 2008). Ring closure by a yet-to-be-identified mechanism might then facilitate the entrapment of the sister chromatids inside the cohesin complex.
cohesin subunit Scc3 are mutated, and based on the finding that these three proteins physically interact with each other, they further speculate that this antiestablishment activity is associated with a cohesin subcomplex comprising Wpl1, Pds5, and Scc3. How could these proteins prevent cohesion establishment, how could this be overcome by Smc3 acetylation, and why would an antiestablishment activity exist in the first place? For all three questions, only speculative answers exist today. Rowland et al. (2009) point out that the antiestablishment activity of Wpl1, Pds5, and Scc3 might be related to their other roles in maintaining cohesion after DNA replication. According to the ring model of cohesin function, these proteins could help to maintain cohesin ring closure around DNA, a function that would have to be transiently overcome during S phase to allow entry of DNA into the ring. In this sense, cohesin rings could be like ‘‘snapgate’’ carabiners, which are kept shut by a spring, with the spring corresponding to Wpl1-Pds5-Scc3 in cohesin. Interestingly, Sutani et al. (2009) observed that cohesin complexes containing the putative acetylmimicking Smc3 mutants are associated with less Pds5 than wild-type cohesin. It is therefore possible that Smc3 acetylation
antagonizes antiestablishment activity by changing molecular interactions between cohesin and Pds5-Wpl1. Alternatively, acetylation could affect Smc3 ATPase activity, which is known to regulate the association of cohesin with DNA. Consistent with this possibility, molecular modeling has predicted that the acetylated residues, K112 and K113, are located in close proximity to the Smc3 ATP-binding site (Ben-Shahar et al., 2008; U¨nal et al., 2008; Rowland et al., 2009). Another mystery that requires further investigation is the paradoxical situation that depletion of Wpl1 in yeast and of Wapl in vertebrate cells leads to opposite phenotypes. It is difficult to imagine that these proteins have adopted completely different functions despite their common evolutionary origin. It is more plausible to assume that Wpl1 and Wapl perform similar functions in mechanistic terms but that defects in these functions lead to different phenotypes in different organisms. There is excellent precedence for such phenomena. For example, inactivation of securin, a regulator of the cohesin protease separase, can either lead to precocious sister chromatid separation or to the opposite phenotype, inhibition of sister chromatid separation, depending on the species studied (reviewed in Peters
2 Molecular Cell 34, April 10, 2009 ª2009 Elsevier Inc.
et al., 2008). This unusual situation could stem from the dual roles played by securin: it functions both as a chaperone, i.e., an activator, and as an inhibitor of separase. Depending on which function is more important in a given species, the resulting phenotypes of securin deletion might, thus, be very different. By analogy, the existence of different Wpl1/Wapl phenotypes in yeast and mammalian cells might indicate that this protein affects multiple aspects of cohesin-DNA interactions, cohesion establishment, cohesion maintenance, and cohesin dissociation. A clear understanding of these processes at the molecular level will require a more detailed mechanistic study of how the interactions between cohesin and DNA are regulated. REFERENCES Ben-Shahar, T.R., Heeger, S., Lehane, C., East, P., Flynn, H., Skehel, M., and Uhlmann, F. (2008). Science 321, 563–566. Gandhi, R., Gillespie, P.J., and Hirano, T. (2006). Curr. Biol. 16, 2406–2417. Kueng, S., Hegemann, B., Peters, B.H., Lipp, J.J., Schleiffer, A., Mechtler, K., and Peters, J.M. (2006). Cell 127, 955–967. Lengronne, A., McIntyre, J., Katou, Y., Kanoh, Y., Hopfner, K.P., Shirahige, K., and Uhlmann, F. (2006). Mol. Cell 23, 787–799. Peters, J.M., Tedeschi, A., and Schmitz, J. (2008). Genes Dev. 22, 3089–3114. Rowland, B.D., Roig, M.B., Nishino, T., Kurze, A., Uluocak, P., Mishra, A., Beckoue¨t, F., Underwood, P., Metson, J., Imre, R., et al. (2009). Mol. Cell 33, 763–774. Skibbens, R.V., Corson, L.B., Koshland, D., and Hieter, P. (1999). Genes Dev. 13, 307–319. Sutani, T., Kawaguchi, T., Kanno, R., Itoh, T., and Shirahige, K. (2009). Curr. Biol. 19, 492–497. Toth, A., Ciosk, R., Uhlmann, F., Galova, M., Schleiffer, A., and Nasmyth, K. (1999). Genes Dev. 13, 320–333. U¨nal, E., Heidinger-Pauli, J.M., Kim, W., Guacci, V., Onn, I., Gygi, S.P., and Koshland, D.E. (2008). Science 321, 566–569. Zhang, J., Shi, X., Li, Y., Kim, B.J., Jia, J., Huang, Z., Yang, T., Fu, X., Jung, S.Y., Wang, Y., et al. (2008). Mol. Cell 31, 143–151.
Preview Cohesin Acetylation: From Antiestablishment to Establishment Jan-Michael Peters1,* and Venugopal Bhaskara1 1Research Institute of Molecular Pathology, Dr. Bohr-Gasse 7, A-1030 Vienna, Austria *Correspondence: [email protected] DOI 10.1016/j.molcel.2009.03.011
In a recent issue of Molecular Cell, Rowland et al. (2009) report that acetylation of cohesin in S phase transiently counteracts an intrinsic ‘‘antiestablishment’’ activity and, thus, enables establishment of sister chromatid cohesion. When one cell divides into two, all of its nuclear DNA must be faithfully duplicated, and the resulting ‘‘sister’’ DNA molecules must remain connected with each other. Without such sister chromatid cohesion, chromosomes cannot biorient on the spindle later in mitosis or meiosis, nor can they symmetrically segregate into the forming daughter cells. The establishment of sister chromatid cohesion during S phase is, therefore, essential for proper cell division. Cohesion is mediated by cohesins, multisubunit protein complexes that have been proposed to connect sister chromatids by encircling them as molecular rings (reviewed in Peters et al., 2008). Interestingly, the association of cohesin with DNA is required, but not sufficient, for building sister chromatid cohesion in S phase. The identity of other factors that render cohesin ‘‘cohesive’’ during DNA replication has remained one of the greatest enigmas in the areas of cell-cycle and chromosome biology research. For almost a decade, little was known about cohesion establishment in S phase, except that in budding yeast this process depends on the Eco1 acetyltransferase (Skibbens et al., 1999; Toth et al., 1999). Interestingly, early genetic experiments showed that Eco1 is needed only during DNA replication, i.e., when cohesion is established, but not afterwards, thus implying that Eco1 is dispensable for the maintenance of cohesion once it has been established (Skibbens et al., 1999; Toth et al., 1999). It also remained unclear if acetyltransferase activity was essential for Eco1’s function and, if so, what Eco1’s critical substrate might be. Both of these questions were answered by a recent series of key publications (Ben-Shahar et al., 2008;
U¨nal et al., 2008; Rowland et al., 2009). Each group reported that one of cohesin’s subunits, the ATPase Smc3, is the critical target of Eco1. Remarkably, the otherwise essential ECO1 gene becomes dispensable for viability in budding yeast if two lysine residues on Smc3 (K112 and K113), which are acetylated by Eco1, are substituted by glutamine or asparagine residues. These amino acids might mimic the acetylated form of lysine, at least in functional terms. This genetic suppression implies that cohesin acetylation is the only essential function of Eco1 in cohesion establishment. A similar situation might exist in mammalian cells, where the Smc3 subunit of the cohesin complex also becomes acetylated during S phase on two lysine residues that correspond to K112 and K113 in budding yeast (Zhang et al., 2008). Interestingly, U¨nal et al. (2008) observed that Smc3 acetylation occurs only following entry into S phase and depends on chromatin association of cohesin, whereas previous work by Uhlmann and colleagues indicated that Eco1 might travel along DNA together with replication forks (Lengronne et al., 2006). Together, these observations support a model in which cohesin is made cohesive at replication forks by Eco1, which acetylates K112 and K113 on Smc3 (Figure 1). How could two small chemical modifications make cohesin cohesive? A crucial hint to this important question comes from the discovery, made by three independent groups (Ben-Shahar et al., 2008; Rowland et al., 2009; Sutani et al., 2009), that Eco1 also becomes dispensable for viability if either of two other genes, PDS5 or WPL1, are mutated. Pds5 is an essential cohesin-binding protein that is required for cohesion, whereas the function of
Wpl1 in yeast (also known as Rad61) was previously poorly understood. Wpl1 is distantly related to vertebrate Wapl (Kueng et al., 2006), a cohesin-associated protein that is required to remove cohesin from DNA and that forms a complex with Pds5 (Gandhi et al., 2006; Kueng et al., 2006). New results show that Wpl1 also binds to Pds5 and associates with DNA at the same sites as cohesin, lending further support to the idea that Wpl1 represents the budding yeast othologue of Wapl (Ben-Shahar et al., 2008; Rowland et al., 2009; Sutani et al., 2009). Could Wpl1, like its vertebrate counterpart, also have a role in removing cohesin from DNA, and if so, could Smc3 acetylation promote cohesion establishment by protecting cohesin from this dissociation activity? Although this model seemed attractive at first, the phenotypic analysis of yeast cells lacking Wpl1 suggests a different view. In contrast to Wapl-depleted vertebrate cells, which have increased amounts of cohesin on their DNA and ‘‘hypercohesed’’ mitotic chromosomes (Gandhi et al., 2006; Kueng et al., 2006), yeast cells lacking Wpl1 have reduced amounts of cohesin bound to chromatin and display mild cohesion defects (Rowland et al., 2009; Sutani et al., 2009). These results indicate that Wpl1 does not have a major role in removing cohesin from DNA and, therefore, are not consistent with the idea that Smc3 acetylation protects cohesin from dissociation. Instead, Rowland et al. (2009) now propose that Smc3 acetylation might antagonize an ‘‘antiestablishment’’ activity, which normally prevents cohesin from becoming cohesive. Based on the observations that Eco1 becomes dispensable if Wpl1 is deleted, or if Pds5 or the
Molecular Cell 34, April 10, 2009 ª2009 Elsevier Inc. 1
Molecular Cell
Preview
Figure 1. A Speculative Model for the Role of Smc3 Acetylation in Cohesion Establishment during DNA Replication Eco1 might acetylate Smc3 specifically at replication forks (the acetylated lysine residues are indicated as red dots). This modification might promote establishment of cohesion by causing transient opening of the cohesin ring, which according to previous work, could occur via separation of the hinge dimerization domains of Smc1 and Smc3 (reviewed in Peters et al., 2008). Ring closure by a yet-to-be-identified mechanism might then facilitate the entrapment of the sister chromatids inside the cohesin complex.
cohesin subunit Scc3 are mutated, and based on the finding that these three proteins physically interact with each other, they further speculate that this antiestablishment activity is associated with a cohesin subcomplex comprising Wpl1, Pds5, and Scc3. How could these proteins prevent cohesion establishment, how could this be overcome by Smc3 acetylation, and why would an antiestablishment activity exist in the first place? For all three questions, only speculative answers exist today. Rowland et al. (2009) point out that the antiestablishment activity of Wpl1, Pds5, and Scc3 might be related to their other roles in maintaining cohesion after DNA replication. According to the ring model of cohesin function, these proteins could help to maintain cohesin ring closure around DNA, a function that would have to be transiently overcome during S phase to allow entry of DNA into the ring. In this sense, cohesin rings could be like ‘‘snapgate’’ carabiners, which are kept shut by a spring, with the spring corresponding to Wpl1-Pds5-Scc3 in cohesin. Interestingly, Sutani et al. (2009) observed that cohesin complexes containing the putative acetylmimicking Smc3 mutants are associated with less Pds5 than wild-type cohesin. It is therefore possible that Smc3 acetylation
antagonizes antiestablishment activity by changing molecular interactions between cohesin and Pds5-Wpl1. Alternatively, acetylation could affect Smc3 ATPase activity, which is known to regulate the association of cohesin with DNA. Consistent with this possibility, molecular modeling has predicted that the acetylated residues, K112 and K113, are located in close proximity to the Smc3 ATP-binding site (Ben-Shahar et al., 2008; U¨nal et al., 2008; Rowland et al., 2009). Another mystery that requires further investigation is the paradoxical situation that depletion of Wpl1 in yeast and of Wapl in vertebrate cells leads to opposite phenotypes. It is difficult to imagine that these proteins have adopted completely different functions despite their common evolutionary origin. It is more plausible to assume that Wpl1 and Wapl perform similar functions in mechanistic terms but that defects in these functions lead to different phenotypes in different organisms. There is excellent precedence for such phenomena. For example, inactivation of securin, a regulator of the cohesin protease separase, can either lead to precocious sister chromatid separation or to the opposite phenotype, inhibition of sister chromatid separation, depending on the species studied (reviewed in Peters
2 Molecular Cell 34, April 10, 2009 ª2009 Elsevier Inc.
et al., 2008). This unusual situation could stem from the dual roles played by securin: it functions both as a chaperone, i.e., an activator, and as an inhibitor of separase. Depending on which function is more important in a given species, the resulting phenotypes of securin deletion might, thus, be very different. By analogy, the existence of different Wpl1/Wapl phenotypes in yeast and mammalian cells might indicate that this protein affects multiple aspects of cohesin-DNA interactions, cohesion establishment, cohesion maintenance, and cohesin dissociation. A clear understanding of these processes at the molecular level will require a more detailed mechanistic study of how the interactions between cohesin and DNA are regulated. REFERENCES Ben-Shahar, T.R., Heeger, S., Lehane, C., East, P., Flynn, H., Skehel, M., and Uhlmann, F. (2008). Science 321, 563–566. Gandhi, R., Gillespie, P.J., and Hirano, T. (2006). Curr. Biol. 16, 2406–2417. Kueng, S., Hegemann, B., Peters, B.H., Lipp, J.J., Schleiffer, A., Mechtler, K., and Peters, J.M. (2006). Cell 127, 955–967. Lengronne, A., McIntyre, J., Katou, Y., Kanoh, Y., Hopfner, K.P., Shirahige, K., and Uhlmann, F. (2006). Mol. Cell 23, 787–799. Peters, J.M., Tedeschi, A., and Schmitz, J. (2008). Genes Dev. 22, 3089–3114. Rowland, B.D., Roig, M.B., Nishino, T., Kurze, A., Uluocak, P., Mishra, A., Beckoue¨t, F., Underwood, P., Metson, J., Imre, R., et al. (2009). Mol. Cell 33, 763–774. Skibbens, R.V., Corson, L.B., Koshland, D., and Hieter, P. (1999). Genes Dev. 13, 307–319. Sutani, T., Kawaguchi, T., Kanno, R., Itoh, T., and Shirahige, K. (2009). Curr. Biol. 19, 492–497. Toth, A., Ciosk, R., Uhlmann, F., Galova, M., Schleiffer, A., and Nasmyth, K. (1999). Genes Dev. 13, 320–333. U¨nal, E., Heidinger-Pauli, J.M., Kim, W., Guacci, V., Onn, I., Gygi, S.P., and Koshland, D.E. (2008). Science 321, 566–569. Zhang, J., Shi, X., Li, Y., Kim, B.J., Jia, J., Huang, Z., Yang, T., Fu, X., Jung, S.Y., Wang, Y., et al. (2008). Mol. Cell 31, 143–151.