1. A Recurrent Phospho-Sumoyl Switch in Transcriptional Repression and Beyond 
Xiang-Jiao Yang, Serge Grégoire 
Molecular Cell 
Volume 23, Issue 6, Pages (September 2006)
DOI: /j.molcel
Copyright © 2006 Elsevier Inc. Terms and Conditions

2. Figure 1 Sequence Characteristics of the Phospho-Sumoyl Switch
(A) Cartoon illustrating stimulation of sumoylation by a neighboring phosphate group. The sequence motif is shown within a rectangle, with the SUMO motif and the phosphate acceptor indicated in orange. For the motif, ψ represents a bulky hydrophobic residue (frequently valine, leucine, or isoleucine), and x is any residue.
(B) Sequence alignment of the sumoylation motif found in HSF1 and HSF4 from human (h), rat (r), mouse (m), Xenopus (x), zebrafish (z), and Gallus (g), with highly conserved residues shaded in green. Arrows denote sumoylated and phosphorylated residues, with responsible kinases also shown.
(C) Comparison of the sumoylation sites present in PPARγ proteins from human (h), rat (r), mouse (m), Xenopus (x), and marine fish (f), with highly conserved residues shaded in green. Of note, PPARγ is also subject to ligand-inducible sumoylation that occurs at a different site (Pascual et al., 2005).
(D) Sequence alignment of the sumoylation motif found in MEF2 from human (h), mouse (m), Xenopus (x), Drosophila (d), and C. elegans (c), with highly conserved residues shaded in green.
Molecular Cell  , DOI: ( /j.molcel )
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3. Figure 2
Sequence Conservation Islands Found in MEF2 and GATA1 Proteins
(A) Comparison of human MEF2C and MEF2D sequences. The alignment is modified from BLASTp search results, with the plus sign denoting conserved substitutions. The region corresponding to the motif ψKxExxSP is highlighted in green and labeled as a conservation island. A similar conservation island is present among MEF2 proteins from humans, Drosophila, and C. elegans (data not shown).
(B) Alignment of human (h) and Xenopus (x) GATA1 sequences, which are derived from NP_ and P23767, respectively. The analysis was done and is illustrated as in (A).
Molecular Cell  , DOI: ( /j.molcel )
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4. Figure 3
Cartoons Depicting Signaling Pathways to Turn On and Off the Phospho-Sumoyl Switch
(A) ERK1 phosphorylates HSF1 on Ser307 and primes Ser303 phosphorylation by GSK3β, which in turn stimulates Lys298 sumoylation and leads to transcriptional repression. Upon dephosphorylation, sumoylation is reversed to activate transcription. The issue of how stress exposure affects GSK3β and an unidentified phosphatase to regulate the sequential modifications awaits further investigation.
(B) Through signaling cascades, a mitogen signal activates ERK2 to phosphorylate PPARγ2 on Ser112, thereby stimulating sumoylation of Lys107 and leading to transcriptional repression. The phosphatase involved remains to be identified.
(C) Kinases such as Cdk5 phosphorylate MEF2 on Ser444 and promote sumoylation of Lys439 (based on positions of human MEF2D), keeping MEF2 in a repressed state. Upon membrane depolarization, calcium influx through voltage-gated channels activates calcineurin to dephosphorylate MEF2 and poise it for activation.
Molecular Cell  , DOI: ( /j.molcel )
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5. Figure 4
Hypothetical Models on How Sequential Phosphorylation and Sumoylation May Exert Effects
(A) The SUMO moiety contains a binding site for recruiting a target that may possess a SUMO-interacting motif (SIM). The question mark denotes that the neighboring phosphate group may or may not affect target recruitment.
(B) Tyr701 phosphorylation of STAT1 promotes a docking site for its own SH2 domain and leads to dimerization for nuclear localization and transcriptional activation. Sumoylation of Lys703 negatively regulates signaling duration, perhaps by inhibiting SH2 association. It remains to be determined whether Ser708 is phosphorylated and, if so, whether phosphorylation stimulates subsequent sumoylation.
(C) Phosphorylation of PPARγ on Ser112 promotes sumoylation of Lys107, which may affect recruitment of WW domain proteins like TAZ and YAP to the PPxY motif. It is also possible that phosphorylation affects the recruitment independent of sumoylation. Further experimentation is needed to distinguish between these possibilities.
Molecular Cell  , DOI: ( /j.molcel )
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