Rnf165/Ark2C enhances BMP-Smad signaling to mediate motor axon extension

Nature's Secret Neuro-Regeneration Pathway in Axolotls, Polychaetes and Planarians for Human Therapeutic Target Pathways

Despite significant improvements in the comprehension of neuro-regeneration, restoring nerve injury in humans continues to pose a substantial therapeutic difficulty. In the peripheral nervous system (PNS), the nerve regeneration process after injury relies on Schwann cells. These cells play a crucial role in regulating and releasing different extracellular matrix proteins, including laminin and fibronectin, which are essential for facilitating nerve regeneration. However, during regeneration, the nerve is required to regenerate for a long distance and, subsequently, loses its capacity to facilitate regeneration during this progression. Meanwhile, it has been noted that nerve regeneration has limited capabilities in the central nervous system (CNS) compared to in the PNS. The CNS contains factors that impede the regeneration of axons following injury to the axons. The presence of glial scar formation results from this unfavourable condition, where glial cells accumulate at the injury site, generating a physical and chemical barrier that hinders the regeneration of neurons. In contrast to humans, several species, such as axolotls, polychaetes, and planarians, possess the ability to regenerate their neural systems following amputation. This ability is based on the vast amount of pluripotent stem cells that have the remarkable capacity to differentiate and develop into any cell within their body. Although humans also possess these cells, their numbers are extremely limited. Examining the molecular pathways exhibited by these organisms has the potential to offer a foundational understanding of the human regeneration process. This review provides a concise overview of the molecular pathways involved in axolotl, polychaete, and planarian neuro-regeneration. It has the potential to offer a new perspective on therapeutic approaches for neuro-regeneration in humans.

SCFOsFBK1 E3 ligase mediates jasmonic acid-induced turnover of OsATL53 and OsCCR14 to regulate lignification of rice anthers and roots

The rice F-box protein OsFBK1, which mediates the turnover of a cinnamoyl CoA-reductase, OsCCR14, has previously been shown to regulate anther and root lignification. Here, we identify OsATL53, a member of the ATL family of RING-H2 proteins that interacts with OsCCR14 in the cytoplasm. OsATL53 was identified in the same yeast two-hybrid library screening as reported previously for OsCCR14, and we show it to have cytoplasmic localization and E3 ligase ubiquitination properties. SCFOsFBK1 mediates turnover of OsATL53 in the cytoplasm and the nucleus, and that of OsCCR14 only in the nucleus, as shown by cell-free degradation assays. Confocal fluorescence lifetime imaging microscopy analyses demonstrate that in presence of jasmonic acid (JA), which plays a role in anther dehiscence, OsATL53-OsCCR14 undergoes conformational changes that trigger the complex to accumulate around the nuclear periphery and signals OsFBK1 to initiate degradation of the proteins in the respective cellular compartments. OsATL53 decreases the enzymatic activity of OsCCR14 and sequesters it in the cytoplasm, thereby regulating the lignification process. Transgenic rice with knockdown of OsATL53 display increased lignin deposition in the anthers and roots compared to the wild type, whilst knockdown of OsCCR14 results in decreased lignin content. Our results show that OsATL53 affects the activity of OsCCR14, and that their JA-induced degradation by SCFOsFBK1 regulates lignification of rice anthers and roots.

The UAS thioredoxin-like domain of UBXN7 regulates E3 ubiquitin ligase activity of RNF111/Arkadia

BACKGROUND

E3 ubiquitin ligases play critical roles in regulating cellular signaling pathways by inducing ubiquitylation of key components. RNF111/Arkadia is a RING E3 ubiquitin ligase that activates TGF-β signaling by inducing ubiquitylation and proteasomal degradation of the transcriptional repressor SKIL/SnoN. In this study, we have sought to identify novel regulators of the E3 ubiquitin ligase activity of RNF111 by searching for proteins that specifically interacts with its RING domain.

RESULTS

We found that UBXN7, a member of the UBA-UBX family, directly interacts with the RING domain of RNF111 or its related E3 RNF165/ARK2C that shares high sequence homology with RNF111. We showed that UBXN7 docks on RNF111 or RNF165 RING domain through its UAS thioredoxin-like domain. Overexpression of UBXN7 or its UAS domain increases endogenous RNF111, while an UBXN7 mutant devoid of UAS domain has no effect. Conversely, depletion of UBXN7 decreases RNF111 protein level. As a consequence, we found that UBXN7 can modulate degradation of the RNF111 substrate SKIL in response to TGF-β signaling. We further unveiled this mechanism of regulation by showing that docking of the UAS domain of UBXN7 inhibits RNF111 ubiquitylation by preventing interaction of the RING domain with the E2 conjugating enzymes. By analyzing the interactome of the UAS domain of UBXN7, we identified that it also interacts with the RING domain of the E3 TOPORS and similarly regulates its E3 ubiquitin ligase activity by impairing E2 binding.

CONCLUSIONS

Taken together, our results demonstrate that UBXN7 acts as a direct regulator for the E3 ubiquitin ligases RNF111, RNF165, and TOPORS and reveal that a thioredoxin-like domain can dock on specific RING domains to regulate their E3 ubiquitin ligase activity.

Epigenetic remodeling by vitamin C potentiates plasma cell differentiation

Ascorbate (vitamin C) is an essential micronutrient in humans. The severe chronic deficiency of ascorbate, termed scurvy, has long been associated with increased susceptibility to infections. How ascorbate affects the immune system at the cellular and molecular levels remained unclear. From a micronutrient analysis, we identified ascorbate as a potent enhancer for antibody response by facilitating the IL-21/STAT3-dependent plasma cell differentiation in mouse and human B cells. The effect of ascorbate is unique as other antioxidants failed to promote plasma cell differentiation. Ascorbate is especially critical during early B cell activation by poising the cells to plasma cell lineage without affecting the proximal IL-21/STAT3 signaling and the overall transcriptome. As a cofactor for epigenetic enzymes, ascorbate facilitates TET2/3-mediated DNA modification and demethylation of multiple elements at the Prdm1 locus. DNA demethylation augments STAT3 association at the Prdm1 promoter and a downstream enhancer, thus ensuring efficient gene expression and plasma cell differentiation. The results suggest that an adequate level of ascorbate is required for antibody response and highlight how micronutrients may regulate the activity of epigenetic enzymes to regulate gene expression. Our findings imply that epigenetic enzymes can function as sensors to gauge the availability of metabolites and influence cell fate decisions.

Ubiquitin and a charged loop regulate the ubiquitin E3 ligase activity of Ark2C

A large family of E3 ligases that contain both substrate recruitment and RING domains confer specificity within the ubiquitylation cascade. Regulation of RING E3s depends on modulating their ability to stabilise the RING bound E2~ubiquitin conjugate in the activated (or closed) conformation. Here we report the structure of the Ark2C RING bound to both a regulatory ubiquitin molecule and an activated E2~ubiquitin conjugate. The structure shows that the RING domain and non-covalently bound ubiquitin molecule together make contacts that stabilise the activated conformation of the conjugate, revealing why ubiquitin is a key regulator of Ark2C activity. We also identify a charged loop N-terminal to the RING domain that enhances activity by interacting with both the regulatory ubiquitin and ubiquitin conjugated to the E2. In addition, the structure suggests how Lys48-linked ubiquitin chains might be assembled by Ark2C and UbcH5b. Together this study identifies features common to RING E3s, as well elements that are unique to Ark2C and related E3s, which enhance assembly of ubiquitin chains.

Attachment of ubiquitin to proteins is tightly regulated and controls many signalling pathways. Here, the authors show that addition of ubiquitin by the RING E3 ligases Arkadia and Ark2C is enhanced by ubiquitin and a charged loop that precedes the RING domain.

A low affinity cis-regulatory BMP response element restricts target gene activation to subsets of Drosophila neurons

Retrograde BMP signaling and canonical pMad/Medea-mediated transcription regulate diverse target genes across subsets of Drosophila efferent neurons, to differentiate neuropeptidergic neurons and promote motor neuron terminal maturation. How a common BMP signal regulates diverse target genes across many neuronal subsets remains largely unresolved, although available evidence implicates subset-specific transcription factor codes rather than differences in BMP signaling. Here we examine the cis-regulatory mechanisms restricting BMP-induced FMRFa neuropeptide expression to Tv4-neurons. We find that pMad/Medea bind at an atypical, low affinity motif in the FMRFa enhancer. Converting this motif to high affinity caused ectopic enhancer activity and eliminated Tv4-neuron expression. In silico searches identified additional motif instances functional in other efferent neurons, implicating broader functions for this motif in BMP-dependent enhancer activity. Thus, differential interpretation of a common BMP signal, conferred by low affinity pMad/Medea binding motifs, can contribute to the specification of BMP target genes in efferent neuron subsets.

Arkadia/RNF111 is a SUMO-targeted ubiquitin ligase with preference for substrates marked with SUMO1-capped SUMO2/3 chain

Modification with SUMO regulates many eukaryotic proteins. Down-regulation of sumoylated forms of proteins involves either their desumoylation, and hence recycling of the unmodified form, or their proteolytic targeting by ubiquitin ligases that recognize their SUMO modification (termed STUbL or ULS). STUbL enzymes such as Uls1 and Slx5-Slx8 in budding yeast or RNF4 and Arkadia/RNF111 in humans bear multiple SUMO interaction motifs to recognize substrates carrying poly-SUMO chains. Using yeast as experimental system and isothermal titration calorimetry, we here show that Arkadia specifically selects substrates carrying SUMO1-capped SUMO2/3 hybrid conjugates and targets them for proteasomal degradation. Our data suggest that a SUMO1-specific binding site in Arkadia with sequence similarity to a SUMO1-binding site in DPP9 is required for targeting endogenous hybrid SUMO conjugates and PML nuclear bodies in human cells. We thus characterize Arkadia as a STUbL with a preference for substrate proteins marked with distinct hybrid SUMO chains.

The cellular functions of poly-SUMO chains of different compositions are not fully understood. Here, the authors characterize Arkadia/RNF111 as a SUMO-targeted ubiquitin ligase that recognizes proteins with hybrid SUMO1-capped SUMO2/3 chains and targets them for proteasomal degradation.

CTLs, a new class of RING-H2 ubiquitin ligases uncovered by YEELL, a motif close to the RING domain that is present across eukaryotes

RING ubiquitin E3 ligases enclose a RING domain for ubiquitin ligase activity and associated domains and/or conserved motifs outside the RING domain that collectively facilitate their classification and usually reveal some of key information related to mechanism of action. Here we describe a new family of E3 ligases that encodes a RING-H2 domain related in sequence to the ATL and BTL RING-H2 domains. This family, named CTL, encodes a motif designed as YEELL that expands 21 amino acids next to the RING-H2 domain that is present across most eukaryotic lineages. E3 ubiquitin ligase BIG BROTHER is a plant CTL that regulates organ size, and SUMO-targeted ubiquitin E3 ligase RNF111/ARKADIA is a vertebrate CTL. Basal animal and vertebrate, as well as fungi species, encode a single CTL gene that constraints the number of paralogs observed in vertebrates. Conversely, as previously described in ATL and BTL families in plants, CTL genes range from a single copy in green algae and 3 to 5 copies in basal species to 9 to 35 copies in angiosperms. Our analysis describes key structural features of a novel family of E3 ubiquitin ligases as an integral component of the set of core eukaryotic genes.

Axon pathfinding for locomotion

Motor neurons of the spinal cord are responsible for the assembly of neuromuscular connections indispensable for basic locomotion and skilled movements. A precise spatial relationship exists between the position of motor neuron cell bodies in the spinal cord and the course of their axonal projections to peripheral muscle targets. Motor neuron innervation of the vertebrate limb is a prime example of this topographic organization and by virtue of its accessibility and predictability has provided access to fundamental principles of motor system development and neuronal guidance. The seemingly basic binary map established by genetically defined motor neuron subtypes that target muscles in the limb is directed by a surprisingly large number of directional cues. Rather than being simply redundant, these converging signaling pathways are hierarchically linked and cooperate to increase the fidelity of axon pathfinding decisions. A current priority is to determine how multiple guidance signals are integrated by individual growth cones and how they synergize to delineate class-specific axonal trajectories.

Split Hand/Foot Malformation Associated with 7q21.3 Microdeletion: A Case Report

Split hand/foot malformation (SHFM) or ectrodactyly is a rare genetic condition affecting limb development. SHFM shows clinical and genetic heterogeneity. It can present as an isolated form or in combination with additional anomalies affecting the long bones (nonsyndromic form) or other organ systems including the craniofacial, genitourinary and ectodermal structures (syndromic ectrodactyly). This study reports a girl with SHFM who also exhibited developmental delay, mild dysmorphic facial features and sensorineural hearing loss. High-resolution banding analysis indicated an interstitial deletion within the 7q21 band. FISH using locus-specific BAC probes confirmed the microdeletion of 7q21.3. Chromosomal microarray analysis also revealed a microdeletion of 1.856 Mb in 7q21.3. However, a larger 8.44-Mb deletion involving bands 7q21.11q21.2 was observed, and the breakpoints were refined. The phenotype and the candidate genes underlying the pathogenesis of this disorder are discussed.

Secondary ubiquitin-RING docking enhances Arkadia and Ark2C E3 ligase activity

RING-domain E3 ligases enhance transfer of ubiquitin to substrate proteins by stabilizing the RING-bound thioester-linked E2∼ubiquitin conjugate in a defined conformation that primes the active site for nucleophilic attack. Here we report that the monomeric RING domains from the human E3 ligases Arkadia and Ark2C bind directly to free ubiquitin with an affinity comparable to that of other dedicated ubiquitin-binding domains. Further work showed that the Ark-like RING domain and the noncovalently bound ubiquitin molecule coordinately stabilize the E2-conjugated ubiquitin (donor ubiquitin) in the 'closed' conformation. Our studies identify the RING domain of Arkadia as a ubiquitin-binding domain and provide insight into a new ubiquitin-dependent mechanism used by monomeric RING domains to activate ubiquitin transfer. This study also suggests how substrates that have been monoubiquitinated could be favored for further ubiquitination.

Bone morphogenetic protein 2–mediated mandible reconstruction successfully heals bony defects but inhibits concurrent inferior alveolar nerve grafting: a rabbit experimental model

BACKGROUND

Bone morphogenetic protein 2 (BMP-2) has been used to reconstruct mandibular defects. An elegant addition to this reconstruction method would be incorporation of a nerve graft wrapped in a BMP-2 carrier to reconstitute the inferior alveolar nerve (IAN) and restore sensation to the lower face. We developed a rabbit model to determine the effect BMP-2 has on nerve regeneration following neurorrhaphy.

METHODS

An inferior border mandibulectomy was created in 16 adult New Zealand white rabbits. The IAN was protected, divided, and repaired with either primary neurorrhaphy or reverse autografts. Bone defects were treated with no treatment controls (n = 2), absorbable collagen sponge (ACS) (vehicle controls) (n = 7), and ACS soaked in BMP-2 (treatment group) (n = 7). Animals underwent computed tomography (CT) 2 days and 6 weeks postoperatively. The percent bone defect healing was calculated using Amira 3D imaging software. At 6 weeks, IANs were harvested mesial to the reconstruction and were evaluated with toluidine blue histology to identify myelinated axons. Reconstructed mandible segments were evaluated with micro-CT and hematoxylin-eosin histology.

RESULTS

Bone morphogenetic protein 2-treated animals demonstrated significantly more bone healing than did the ACS and empty defect groups (82%, 38%, 44%, respectively; P < 0.01). One hundred percent of ACS-treated nerves (n = 4) demonstrated axon regrowth, whereas only 25% of BMP-2-treated nerves (n = 4) did. Micro-CT and histology showed BMP-2 caused bone growth around the IAN, but regenerated bone infiltrated the repair site and created a physical barrier to axon growth.

CONCLUSIONS

Bone morphogenetic protein 2 can successfully heal bone defects in the rabbit mandible, but ectopic bone growth can inhibit IAN recovery after repair. Level of Evidence: Not gradable.

Single-stranded γPNAs for in vivo site-specific genome editing via Watson-Crick recognition

Triplex-forming peptide nucleic acids (PNAs) facilitate gene editing by stimulating recombination of donor DNAs within genomic DNA via site-specific formation of altered helical structures that further stimulate DNA repair. However, PNAs designed for triplex formation are sequence restricted to homopurine sites. Herein we describe a novel strategy where next generation single-stranded gamma PNAs (γPNAs) containing miniPEG substitutions at the gamma position can target genomic DNA in mouse bone marrow at mixed-sequence sites to induce targeted gene editing. In addition to enhanced binding, γPNAs confer increased solubility and improved formulation into poly(lactic-co-glycolic acid) (PLGA) nanoparticles for efficient intracellular delivery. Single-stranded γPNAs induce targeted gene editing at frequencies of 0.8% in mouse bone marrow cells treated ex vivo and 0.1% in vivo via IV injection, without detectable toxicity. These results suggest that γPNAs may provide a new tool for induced gene editing based on Watson-Crick recognition without sequence restriction.

Genomic profiling screens small molecules of metastatic prostate carcinoma

The aim of the present study was to investigate the pathogenesis of metastatic prostate carcinoma, to find the metabolic pathways changed in the disease and to screen out the potential therapeutic drugs. GSE38241 was downloaded from Gene Expression Omnibus; the Geoquery package was applied to preprocessed expression profiling, and the differentially-expressed genes (DEGs) were selected with limma (linear regression model packages). Next, WikiPathways cluster analysis was performed for DEGs on a Gene Set Analysis Toolkit V2 platform, and DEGs with hypergeometric algorithms were calculated through gene set enrichment analysis. A total of 1,126 DEGs were identified between the normal prostate and metastatic prostate carcinoma. In addition, KPNA4, SYT1, PLCB1, SPRED1, MBNL2, RNF165, MEF2C, MBNL1, ZFP36L1 and CELF2, were found to be likely to play significant roles in the process of metastatic prostate carcinoma. The small molecules STOCK1N-35874 and 5182598 could simulate the state of normal cells well, while the small molecules MS-275 and quinostatin could simulate the state of metastatic prostate carcinoma cells. In conclusions, the small molecules STOCK1N-35874 and 5182598 were identified to be good potential therapeutic drugs for the treatment of metastatic prostate carcinoma, while the two small molecules MS-275 and quinostatin could cause metastatic prostate carcinoma.

Deconstruction of DNA methylation patterns during myogenesis reveals specific epigenetic events in the establishment of the skeletal muscle lineage

The progressive restriction of differentiation potential from pluripotent embryonic stem cells (ESCs) to tissue-specific stem cells involves widespread epigenetic reprogramming, including modulation of DNA methylation patterns. Skeletal muscle stem cells are required for the growth, maintenance, and regeneration of skeletal muscle. To investigate the contribution of DNA methylation to the establishment of the myogenic program, we analyzed ESCs, skeletal muscle stem cells in proliferating (myoblasts) and differentiating conditions (myotubes), and mature myofibers. About 1.000 differentially methylated regions were identified during muscle-lineage determination and terminal differentiation, mainly located in gene bodies and intergenic regions. As a whole, myogenic stem cells showed a gain of DNA methylation, while muscle differentiation was accompanied by loss of DNA methylation in CpG-poor regions. Notably, the hypomethylated regions in myogenic stem cells were neighbored by enhancer-type chromatin, suggesting the involvement of DNA methylation in the regulation of cell-type specific enhancers. Interestingly, we demonstrated the hypomethylation of the muscle cell-identity Myf5 super-enhancer only in muscle cells. Furthermore, we observed that upstream stimulatory factor 1 binding to Myf5 super-enhancer occurs upon DNA demethylation in myogenic stem cells. Taken altogether, we characterized the unique DNA methylation signature of skeletal muscle stem cells and highlighted the importance of DNA methylation-mediated regulation of cell identity Myf5 super-enhancer during cellular differentiation.

Celsr3 and Fzd3 in axon guidance

The assembly of functional neuronal circuits depends on the correct wiring of axons and dendrites. To reach their targets, axons are guided by a variety of extracellular guidance cues, including Netrins, Ephrins, Semaphorins and Slits. Corresponding receptors in the growth cone, the dynamic structure at the tip of the growing axon, sense and integrate these positional signals, and activate downstream effectors to regulate cytoskeletal organization. In addition to the four canonical families of axon guidance cues mentioned above, some proteins that regulate planar cell polarity were recently found to be critical for axon guidance. The seven-transmembrane domain receptors Celsr3 and Fzd3, in particular, control the development of most longitudinal tracts in the central nervous system, and axon navigation in the peripheral, sympathetic and enteric nervous systems. Despite their unequivocally important role, however, underlying molecular mechanisms remain elusive. We do not know which extracellular ligands they recognize, whether they have co-receptors in the growth cone, and what their downstream effectors are. Here, we review some recent advances and discuss future trends in this emerging field.

Bone morphogenetic protein signaling in vertebrate motor neurons and neuromuscular communication

An accurate communication between motor neurons and skeletal muscle fibers is required for the proper assembly, growth and maintenance of neuromuscular junctions (NMJs). Several signaling and extracellular matrix molecules play stimulatory and inhibitory roles on the assembly of functional synapses. Studies in Drosophila have revealed crucial functions for early morphogens, such as members of the Wnt and Bone Morphogenetic Proteins (BMP) signaling pathways, during the assembly and maturation of the NMJ. Here, we bring together recent findings that led us to propose that BMPs also work in vertebrate organisms as diffusible cues to communicate motor neurons and skeletal muscles.

Zebrafish Rnf111 is encoded by multiple transcripts and is required for epiboly progression and prechordal plate development

Arkadia (also known as RING finger 111) encodes a nuclear E3 ubiquitin ligase that targets intracellular effectors and modulators of TGFβ/Nodal-related signaling for polyubiquitination and proteasome-dependent degradation. In the mouse, loss of Arkadia results in early embryonic lethality, with defects attributed to compromised Nodal signaling. Here, we report the isolation of zebrafish arkadia/rnf111, which is represented by 5 transcript variants. arkadia/rnf111 is broadly expressed during the blastula and gastrula stages, with eventual enrichment in the anterior mesendoderm, including the prechordal plate. Morpholino knockdown experiments reveal an unexpected role for Arkadia/Rnf111 in both early blastula organization and epiboly progression. Using a splice junction morpholino, we present additional evidence that arkadia/rnf111 transcript variants containing a 3' alternative exon are specifically required for epiboly progression in the late gastrula. This result suggests that arkadia/rnf111 transcript variants encode functionally relevant protein isoforms that provide additional intracellular flexibility and regulation to the Nodal signaling pathway.

BMP signaling in axon regeneration

Neuronal competence to re-extend axons and a permissive environment that allows growth cone navigation are two major determinants for successful axon regeneration. Here, we review the roles of bone morphogenetic protein (BMP) signaling in mediating both neuronal and glial injury responses after CNS injury. BMPs can activate a pro-regenerative transcription program in neurons through Smad-mediated canonical pathway, or act locally on cytoskeleton assembly at distal axons via non-canonical pathways. Emerging evidence implicates retrograde BMP signalosomes in connecting the cytoskeletal and nuclear responses. In addition, BMP/Smad signaling modulates neurotrophin-mediated axonal outgrowth, and interacts with the epigenetic machinery to initiate epigenetic reprogramming for axon regeneration. Besides their influences on neurons, BMPs also regulate astrogliosis, inflammatory processes, and neural progenitor cell differentiation at the injury site, all of which can either positively or negatively modify the injury microenvironment. Lastly, an increasing number of BMP signaling partners, sensitizers, and downstream effectors collectively fine-tune the signaling intensity and spatiotemporal dynamics of BMP activity in an integrated signaling network during axon regeneration.

Multiple Arkadia/RNF111 structures coordinate its Polycomb body association and transcriptional control

The RING domain protein Arkadia/RNF111 is a ubiquitin ligase in the transforming growth factor β (TGFβ) pathway. We previously identified Arkadia as a small ubiquitin-like modifier (SUMO)-binding protein with clustered SUMO-interacting motifs (SIMs) that together form a SUMO-binding domain (SBD). However, precisely how SUMO interaction contributes to the function of Arkadia was not resolved. Through analytical molecular and cell biology, we found that the SIMs share redundant function with Arkadia's M domain, a region distinguishing Arkadia from its paralogs ARKL1/ARKL2 and the prototypical SUMO-targeted ubiquitin ligase (STUbL) RNF4. The SIMs and M domain together promote both Arkadia's colocalization with CBX4/Pc2, a component of Polycomb bodies, and the activation of a TGFβ pathway transcription reporter. Transcriptome profiling through RNA sequencing showed that Arkadia can both promote and inhibit gene expression, indicating that Arkadia's activity in transcriptional control may depend on the epigenetic context, defined by Polycomb repressive complexes and DNA methylation.

Regulation of transcription factor activity by interconnected post-translational modifications

Transcription factors comprise just over 7% of the human proteome and serve as gatekeepers of cellular function, integrating external signal information into gene expression programs that reconfigure cellular physiology at the most basic levels. Surface-initiated cell signaling pathways converge on transcription factors, decorating these proteins with an array of post-translational modifications (PTMs) that are often interdependent, being linked in time, space, and combinatorial function. These PTMs orchestrate every activity of a transcription factor over its entire lifespan--from subcellular localization to protein-protein interactions, sequence-specific DNA binding, transcriptional regulatory activity, and protein stability--and play key roles in the epigenetic regulation of gene expression. The multitude of PTMs of transcription factors also offers numerous potential points of intervention for development of therapeutic agents to treat a wide spectrum of diseases. We review PTMs most commonly targeting transcription factors, focusing on recent reports of sequential and linked PTMs of individual factors.