Conversion of a Single Polypharmacological Agent into Selective Bivalent Inhibitors of Intracellular Kinase Activity

Molecular Determinants of Affinity and Isoform Selectivity in Protein─Small Molecule Hybrid Inhibitors of Carbonic Anhydrase

Multiple studies have demonstrated the benefit of engineering hybrid ligands that combine the unique benefits of small molecules and proteins or peptides. However, the molecular complexity of hybrid ligands generates a parameter space so large it cannot be exhaustively explored. We systematically evaluated the impact of one molecular design element, conjugation site, on the discovery of functional protein-small molecule hybrids (PriSMs). We utilized a library of yeast-displayed fibronectin domain variants with amino acid and loop length diversity in the paratope and a single cysteine at one of 18 possible conjugation sites. The protein variants were coupled with maleimide-functionalized acetazolamide and sorted via competitive flow cytometry to discover potent and selective inhibitors of three isoforms of carbonic anhydrase. Deep sequencing of the resultant populations of functional PriSMs revealed an isoform-dependent distribution of conjugation site preferences. The top PriSMs showed potency and selectivity gains up to 23- and 100-fold (in this case, for CA-II vs CA-XII, with a 43-fold selectivity gain for CA-II vs CA-IX) relative to PEG2-acetazolamide alone. The presented study expands our fundamental understanding of the role of conjugation site in PriSM function and informs future PriSM engineering efforts by highlighting the benefit of conjugation site diversity in PriSM libraries.

CDRxAbs: antibody small-molecule conjugates with computationally designed target-binding synergy

Bioconjugates as therapeutic modalities combine the advantages and offset the disadvantages of their constituent parts to achieve a refined spectrum of action. We combine the concept of bioconjugation with the full atomic simulation capability of computational protein design to define a new class of molecular recognition agents: CDR-extended antibodies, abbreviated as CDRxAbs. A CDRxAb incorporates a covalently attached small molecule into an antibody/target binding interface using computational protein design to create an antibody small-molecule conjugate that binds tighter to the target of the small molecule than the small molecule would alone. CDRxAbs are also expected to increase the target binding specificity of their associated small molecules. In a proof-of-concept study using monomeric streptavidin/biotin pairs at either a nanomolar or micromolar-level initial affinity, we designed nanobody-biotin conjugates that exhibited >20-fold affinity improvement against their protein targets with step-wise optimization of binding kinetics and overall protein stability. The workflow explored through this process promises a novel approach to optimize small-molecule based therapeutics and to explore new chemical and target space for molecular-recognition agents in general.

Structure-Guided Drug Design Targeting Abl Kinase: How Structure and Regulation Can Assist in Designing New Drugs

The human protein Abelson kinase (Abl), a tyrosine kinase, plays a pivotal role in developing chronic myeloid leukemia (CML). Abl's involvement in various signaling pathways underscores its significance in regulating fundamental biological processes, including DNA damage responses, actin polymerization, and chromatin structural changes. The discovery of the Bcr-Abl oncoprotein, resulting from a chromosomal translocation in CML patients, revolutionized the understanding and treatment of the disease. The introduction of targeted therapies, starting with interferon-alpha and culminating in the development of tyrosine kinase inhibitors (TKIs) like imatinib, significantly improved patient outcomes. However, challenges such as drug resistance and side effects persist, indicating the necessity of research into novel therapeutic strategies. This review describes advancements in Abl kinase inhibitor development, emphasizing rational compound design from structural and regulatory information. Strategies, including bivalent inhibitors, PROTACs, and compounds targeting regulatory domains, promise to overcome resistance and minimize side effects. Additionally, leveraging the intricate structure and interactions of Bcr-Abl may provide insights into developing inhibitors for other kinases. Overall, this review highlights the importance of continued research into Abl kinase inhibition and its broader implications for therapeutic interventions targeting kinase-driven diseases. It provides valuable insights and strategies that may guide the development of next-generation therapies.

Systematic Evaluation of Protein-Small Molecule Hybrids on the Yeast Surface

Protein-small molecule hybrids are structures that have the potential to combine the inhibitory properties of small molecules and the specificities of binding proteins. However, achieving such synergies is a substantial engineering challenge with fundamental principles yet to be elucidated. Recent work has demonstrated the power of the yeast display-based discovery of hybrids using a combination of fibronectin-binding domains and thiol-mediated conjugations to introduce small-molecule warheads. Here, we systematically study the effects of expanding the chemical diversity of these hybrids on the yeast surface by investigating a combinatorial set of fibronectins, noncanonical amino acid (ncAA) substitutions, and small-molecule pharmacophores. Our results show that previously discovered thiol-fibronectin hybrids are generally tolerant of a range of ncAA substitutions and retain binding functions to carbonic anhydrases following click chemistry-mediated assembly of hybrids with diverse linker structures. Most surprisingly, we identified several cases where replacement of a potent acetazolamide warhead with a substantially weaker benzenesulfonamide warhead still resulted in the assembly of multiple functional hybrids. In addition to these unexpected findings, we expanded the throughput of our system by validating a 96-well plate-based format to produce yeast-displayed hybrid conjugates in parallel. These efficient explorations of hybrid chemical diversity demonstrate that there are abundant opportunities to expand the functions of protein-small molecule hybrids and elucidate principles that dictate their efficient discovery and design.

Designing drugs and chemical probes with the dualsteric approach

Traditionally, drugs are monovalent, targeting only one site on the protein surface. This includes orthosteric and allosteric drugs, which bind the protein at orthosteric and allosteric sites, respectively. Orthosteric drugs are good in potency, whereas allosteric drugs have better selectivity and are solutions to classically undruggable targets. However, it would be difficult to simultaneously reach high potency and selectivity when targeting only one site. Also, both kinds of monovalent drugs suffer from mutation-caused drug resistance. To overcome these obstacles, dualsteric modulators have been proposed in the past twenty years. Compared to orthosteric or allosteric drugs, dualsteric modulators are bivalent (or bitopic) with two pharmacophores. Each of the two pharmacophores bind the protein at the orthosteric and an allosteric site, which could bring the modulator with special properties beyond monovalent drugs. In this study, we comprehensively review the current development of dualsteric modulators. Our main effort reason and illustrate the aims to apply the dualsteric approach, including a "double win" of potency and selectivity, overcoming mutation-caused drug resistance, developments of function-biased modulators, and design of partial agonists. Moreover, the strengths of the dualsteric technique also led to its application outside pharmacy, including the design of highly sensitive fluorescent tracers and usage as molecular rulers. Besides, we also introduced drug targets, designing strategies, and validation methods of dualsteric modulators. Finally, we detail the conclusions and perspectives.

Protein Engineering and High-Throughput Screening by Yeast Surface Display: Survey of Current Methods

Yeast surface display (YSD) is a powerful tool in biotechnology that links genotype to phenotype. In this review, the latest advancements in protein engineering and high-throughput screening based on YSD are covered. The focus is on innovative methods for overcoming challenges in YSD in the context of biotherapeutic drug discovery and diagnostics. Topics ranging from titrating avidity in YSD using transcriptional control to the development of serological diagnostic assays relying on serum biopanning and mitigation of unspecific binding are covered. Screening techniques against nontraditional cellular antigens, such as cell lysates, membrane proteins, and extracellular matrices are summarized and techniques are further delved into for expansion of the chemical repertoire, considering protein-small molecule hybrids and noncanonical amino acid incorporation. Additionally, in vivo gene diversification and continuous evolution in yeast is discussed. Collectively, these techniques enhance the diversity and functionality of engineered proteins isolated via YSD, broadening the scope of applications that can be addressed. The review concludes with future perspectives and potential impact of these advancements on protein engineering. The goal is to provide a focused summary of recent progress in the field.

DELs enable the development of BRET probes for target engagement studies in cells

DNA-encoded libraries (DELs) provide unmatched chemical diversity and starting points for novel drug modalities. Here, we describe a workflow that exploits the bifunctional attributes of DEL ligands as a platform to generate BRET probes for live cell target engagement studies. To establish proof of concept, we performed a DEL screen using aurora kinase A and successfully converted aurora DEL ligands as cell-active BRET probes. Aurora BRET probes enabled the validation and stratification of the chemical series identified from primary selection data. Furthermore, we have evaluated the effective repurposing of pre-existing DEL screen data to find suitable leads for BRET probe development. Our findings support the use of DEL workflows as an engine to create cell-active BRET probes independent of structure or compound SAR. The combination of DEL and BRET technology accelerates hit-to-lead studies in a live cell setting.

Kaleidoscope megamolecules synthesis and application using self-assembly technology

The megamolecules with high ordered structures play an important role in chemical biology and biomedical engineering. Self-assembly, a long-discovered but very appealing technique, could induce many reactions between biomacromolecules and organic linking molecules, such as an enzyme domain and its covalent inhibitors. Enzyme and its small-molecule inhibitors have achieved many successes in medical application, which realize the catalysis process and theranostic function. By employing the protein engineering technology, the building blocks of enzyme fusion protein and small molecule linker can be assembled into a novel architecture with the specified organization and conformation. Molecular level recognition of enzyme domain could provide both covalent reaction sites and structural skeleton for the functional fusion protein. In this review, we will discuss the range of tools available to combine functional domains by using the recombinant protein technology, which can assemble them into precisely specified architectures/valences and develop the kaleidoscope megamolecules for catalytic and medical application.

Multitargeting the Action of 5-HT6 Serotonin Receptor Ligands by Additional Modulation of Kinases in the Search for a New Therapy for Alzheimer's Disease: Can It Work from a Molecular Point of View?

In view of the unsatisfactory treatment of cognitive disorders, in particular Alzheimer’s disease (AD), the aim of this review was to perform a computer-aided analysis of the state of the art that will help in the search for innovative polypharmacology-based therapeutic approaches to fight against AD. Apart from 20-year unrenewed cholinesterase- or NMDA-based AD therapy, the hope of effectively treating Alzheimer’s disease has been placed on serotonin 5-HT₆ receptor (5-HT₆R), due to its proven, both for agonists and antagonists, beneficial procognitive effects in animal models; however, research into this treatment has so far not been successfully translated to human patients. Recent lines of evidence strongly emphasize the role of kinases, in particular microtubule affinity-regulating kinase 4 (MARK4), Rho-associated coiled-coil-containing protein kinase I/II (ROCKI/II) and cyclin-dependent kinase 5 (CDK5) in the etiology of AD, pointing to the therapeutic potential of their inhibitors not only against the symptoms, but also the causes of this disease. Thus, finding a drug that acts simultaneously on both 5-HT₆R and one of those kinases will provide a potential breakthrough in AD treatment. The pharmacophore- and docking-based comprehensive literature analysis performed herein serves to answer the question of whether the design of these kind of dual agents is possible, and the conclusions turned out to be highly promising.

Engineered protein-small molecule conjugates empower selective enzyme inhibition

Potent, specific ligands drive precision medicine and fundamental biology. Proteins, peptides, and small molecules constitute effective ligand classes. Yet greater molecular diversity would aid the pursuit of ligands to elicit precise biological activity against challenging targets. We demonstrate a platform to discover protein-small molecule (PriSM) hybrids to combine unique pharmacophore activities and shapes with constrained, efficiently engineerable proteins. In this platform, a fibronectin protein library is displayed on yeast with a single cysteine coupled to acetazolamide via a maleimide-poly(ethylene glycol) linker. Magnetic and flow cytometric sorts enrich specific binders to carbonic anhydrase isoforms. Isolated PriSMs exhibit potent, specific inhibition of carbonic anhydrase isoforms with efficacy superior to that of acetazolamide or protein alone, including an 80-fold specificity increase and 9-fold potency gain. PriSMs are engineered with multiple linker lengths, protein conjugation sites, and sequences against two different isoforms, which reveal platform flexibility and impacts of molecular designs. PriSMs advance the molecular diversity of efficiently engineerable ligands.

Proteomics in the pharmaceutical and biotechnology industry: a look to the next decade

INTRODUCTION

Pioneering technologies such as proteomics have helped fuel the biotechnology and pharmaceutical industry with the discovery of novel targets and an intricate understanding of the activity of therapeutics and their various activities in vitro and in vivo. The field of proteomics is undergoing an inflection point, where new sensitive technologies are allowing intricate biological pathways to be better understood, and novel biochemical tools are pivoting us into a new era of chemical proteomics and biomarker discovery. In this review, we describe these areas of innovation, and discuss where the fields are headed in terms of fueling biotechnological and pharmacological research and discuss current gaps in the proteomic technology landscape.

AREAS COVERED

Single cell sequencing and single molecule sequencing. Chemoproteomics. Biological matrices and clinical samples including biomarkers. Computational tools including instrument control software, data analysis.

EXPERT OPINION

Proteomics will likely remain a key technology in the coming decade, but will have to evolve with respect to type and granularity of data, cost and throughput of data generation as well as integration with other technologies to fulfill its promise in drug discovery.

BET bromodomain inhibitors regulate keratinocyte plasticity

Although most acute skin wounds heal rapidly, non-healing skin ulcers represent an increasing and substantial unmet medical need that urgently requires effective therapeutics. Keratinocytes resurface wounds to re-establish the epidermal barrier by transitioning to an activated, migratory state, but this ability is lost in dysfunctional chronic wounds. Small-molecule regulators of keratinocyte plasticity with the potential to reverse keratinocyte malfunction in situ could offer a novel therapeutic approach in skin wound healing. Utilizing high-throughput phenotypic screening of primary keratinocytes, we identify such small molecules, including bromodomain and extra-terminal domain (BET) protein family inhibitors (BETi). BETi induce a sustained activated, migratory state in keratinocytes in vitro, increase activation markers in human epidermis ex vivo and enhance skin wound healing in vivo. Our findings suggest potential clinical utility of BETi in promoting keratinocyte re-epithelialization of skin wounds. Importantly, this novel property of BETi is exclusively observed after transient low-dose exposure, revealing new potential for this compound class.

Recent advances in development of hetero-bivalent kinase inhibitors

Identifying a pharmacological agent that targets only one of more than 500 kinases present in humans is an important challenge. One potential solution to this problem is the development of bivalent kinase inhibitors, which consist of two connected fragments, each bind to a dissimilar binding site of the bisubstrate enzyme. The main advantage of bivalent (type V) kinase inhibitors is generating more interactions with target enzymes that can enhance the molecules' selectivity and affinity compared to single-site inhibitors. Earlier type V inhibitors were not suitable for the cellular environment and were mostly used in in vitro studies. However, recently developed bivalent compounds have high kinase affinity, high biological and chemical stability in vivo. This review summarized the hetero-bivalent kinase inhibitors described in the literature from 2014 to the present. We attempted to classify the molecules by serine/threonine and tyrosine kinase inhibitors, and then each target kinase and its hetero-bivalent inhibitor was assessed in depth. In addition, we discussed the analysis of advantages, limitations, and perspectives of bivalent kinase inhibitors compared with the monovalent kinase inhibitors.

A mass spectrometry-based proteome map of drug action in lung cancer cell lines

Mass spectrometry-based discovery proteomics is an essential tool for the proximal readout of cellular drug action. Here, we apply a robust proteomic workflow to rapidly profile the proteomes of five lung cancer cell lines in response to more than 50 drugs. Integration of millions of quantitative protein-drug associations substantially improved the mechanism of action (MoA) deconvolution of single compounds. For example, MoA specificity increased after removal of proteins that frequently responded to drugs and the aggregation of proteome changes across cell lines resolved compound effects on proteostasis. We leveraged these findings to demonstrate efficient target identification of chemical protein degraders. Aggregating drug response across cell lines also revealed that one-quarter of compounds modulated the abundance of one of their known protein targets. Finally, the proteomic data led us to discover that inhibition of mitochondrial function is an off-target mechanism of the MAP2K1/2 inhibitor PD184352 and that the ALK inhibitor ceritinib modulates autophagy.

Avoiding or Co-Opting ATP Inhibition: Overview of Type III, IV, V, and VI Kinase Inhibitors

As described in the previous chapter, most kinase inhibitors that have been developed for use in the clinic act by blocking ATP binding; however, there is growing interest in identifying compounds that target kinase activities and functions without interfering with the conserved features of the ATP-binding site. This chapter will highlight alternative approaches that exploit unique kinase structural features that are being targeted to identify more selective and potent inhibitors. The figure below, adapted from (Sammons et al., Molecular Carcinogenesis 58:1551–1570, 2019), provides a graphical description of the various approaches to manipulate kinase activity. In addition to the type I and II inhibitors, type III kinase inhibitors have been identified to target sites adjacent to the ATP-binding site in the catalytic domain. New information on kinase structure and substrate-binding sites has enabled the identification of type IV kinase inhibitor compounds that target regions outside the catalytic domain. The combination of targeting unique allosteric sites outside the catalytic domain with ATP-targeted compounds has yielded a number of novel bivalent type V kinase inhibitors. Finally, emerging interest in the development of irreversible compounds that form selective covalent interactions with key amino acids involved in kinase functions comprise the class of type VI kinase inhibitors.

Subcellular drug targeting illuminates local kinase action

Deciphering how signaling enzymes operate within discrete microenvironments is fundamental to understanding biological processes. A-kinase anchoring proteins (AKAPs) restrict the range of action of protein kinases within intracellular compartments. We exploited the AKAP targeting concept to create genetically encoded platforms that restrain kinase inhibitor drugs at distinct subcellular locations. Local Kinase Inhibition (LoKI) allows us to ascribe organelle-specific functions to broad specificity kinases. Using chemical genetics, super resolution microscopy, and live-cell imaging we discover that centrosomal delivery of Polo-like kinase 1 (Plk1) and Aurora A (AurA) inhibitors attenuates kinase activity, produces spindle defects, and prolongs mitosis. Targeted inhibition of Plk1 in zebrafish embryos illustrates how centrosomal Plk1 underlies mitotic spindle assembly. Inhibition of kinetochore-associated pools of AurA blocks phosphorylation of microtubule-kinetochore components. This versatile precision pharmacology tool enhances investigation of local kinase biology.

CPSF3-dependent pre-mRNA processing as a druggable node in AML and Ewing's sarcoma

The post-genomic era has seen many advances in our understanding of cancer pathways, yet resistance and tumor heterogeneity necessitate multiple approaches to target even monogenic tumors. Here, we combine phenotypic screening with chemical genetics to identify pre-messenger RNA endonuclease cleavage and polyadenylation specificity factor 3 (CPSF3) as the target of JTE-607, a small molecule with previously unknown target. We show that CPSF3 represents a synthetic lethal node in a subset of acute myeloid leukemia (AML) and Ewing's sarcoma cancer cell lines. Inhibition of CPSF3 by JTE-607 alters expression of known downstream effectors in AML and Ewing's sarcoma lines, upregulates apoptosis and causes tumor-selective stasis in mouse xenografts. Mechanistically, it prevents the release of newly synthesized pre-mRNAs, resulting in read-through transcription and the formation of DNA-RNA hybrid R-loop structures. This study implicates pre-mRNA processing, and specifically CPSF3, as a druggable target providing an avenue to therapeutic intervention in cancer.

A High Content Screen in Macrophages Identifies Small Molecule Modulators of STING-IRF3 and NFkB Signaling

We screened a library of bioactive small molecules for activators and inhibitors of innate immune signaling through IRF3 and NFkB pathways with the goals of advancing pathway understanding and discovering probes for immunology research. We used high content screening to measure the translocation from the cytoplasm to nucleus of IRF3 and NFkB in primary human macrophages; these transcription factors play a critical role in the activation of STING and other pro-inflammatory pathways. Our pathway activator screen yielded a diverse set of hits that promoted nuclear translocation of IRF3 and/or NFkB, but the majority of these compounds did not cause activation of downstream pathways. Screening for antagonists of the STING pathway yielded multiple kinase inhibitors, some of which inhibit kinases not previously known to regulate the activity of this pathway. Structure-activity relationships (SARs) and subsequent chemical proteomics experiments suggested that MAPKAPK5 (PRAK) is a kinase that regulates IRF3 translocation in human macrophages. Our work establishes a high content screening approach for measuring pro-inflammatory pathways in human macrophages and identifies novel ways to inhibit such pathways; among the targets of the screen are several molecules that may merit further development as anti-inflammatory drugs.

Quantitative, Wide-Spectrum Kinase Profiling in Live Cells for Assessing the Effect of Cellular ATP on Target Engagement

For kinase inhibitors, intracellular target selectivity is fundamental to pharmacological mechanism. Although a number of acellular techniques have been developed to measure kinase binding or enzymatic inhibition, such approaches can fail to accurately predict engagement in cells. Here we report the application of an energy transfer technique that enabled the first broad-spectrum, equilibrium-based approach to quantitatively profile target occupancy and compound affinity in live cells. Using this method, we performed a selectivity profiling for clinically relevant kinase inhibitors against 178 full-length kinases, and a mechanistic interrogation of the potency offsets observed between cellular and biochemical analysis. For the multikinase inhibitor crizotinib, our approach accurately predicted cellular potency and revealed improved target selectivity compared with biochemical measurements. Due to cellular ATP, a number of putative crizotinib targets are unexpectedly disengaged in live cells at a clinically relevant drug dose.

Examining the influence of specificity ligands and ATP-competitive ligands on the overall effectiveness of bivalent kinase inhibitors

Background

Identifying selective kinase inhibitors remains a major challenge. The design of bivalent inhibitors provides a rational strategy for accessing potent and selective inhibitors. While bivalent kinase inhibitors have been successfully designed, no comprehensive assessment of affinity and selectivity for a series of bivalent inhibitors has been performed. Here, we present an evaluation of the structure activity relationship for bivalent kinase inhibitors targeting ABL1.

Methods

Various SNAPtag constructs bearing different specificity ligands were expressed in vitro. Bivalent inhibitor formation was accomplished by synthesizing individual ATP-competitive kinase inhibitors containing a SNAPtag targeting moiety, enabling the spontaneous self-assembly of the bivalent inhibitor. Assembled bivalent inhibitors were incubated with K562 lysates, and then subjected to affinity enrichment using various ATP-competitive inhibitors immobilized to sepharose beads. Resulting eluents were analyzed using Tandem Mass Tag (TMT) labeling and two-dimensional liquid chromatography-tandem mass spectrometry (2D–LC-MS/MS). Relative binding affinity of the bivalent inhibitor was determined by calculating the concentration at which 50% of a given kinase remained bound to the affinity matrix.

Results

The profiling of three parental ATP-competitive inhibitors and nine SNAPtag conjugates led to the identification of 349 kinase proteins. In all cases, the bivalent inhibitors exhibited enhanced binding affinity and selectivity for ABL1 when compared to the parental compound conjugated to SNAPtag alone. While the rank order of binding affinity could be predicted by considering the binding affinities of the individual specificity ligands, the resulting affinity of the assembled bivalent inhibitor was not predictable. The results from this study suggest that as the potency of the ATP-competitive ligand increases, the contribution of the specificity ligand towards the overall binding affinity of the bivalent inhibitor decreases. However, the affinity of the specificity components in its interaction with the target is essential for achieving selectivity.

Conclusion

Through comprehensive chemical proteomic profiling, this work provides the first insight into the influence of ATP-competitive and specificity ligands binding to their intended target on a proteome-wide scale. The resulting data suggest a subtle interplay between the ATP-competitive and specificity ligands that cannot be accounted for by considering the specificity or affinity of the individual components alone.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-017-0125-1) contains supplementary material, which is available to authorized users.

Bivalent Inhibitors of c-Src Tyrosine Kinase That Bind a Regulatory Domain

We have developed a general methodology to produce bivalent kinase inhibitors for c-Src that interact with the SH2 and ATP binding pockets. Our approach led to a highly selective bivalent inhibitor of c-Src. We demonstrate impressive selectivity for c-Src over homologous kinases. Exploration of the unexpected high level of selectivity yielded insight into the inherent flexibility of homologous kinases. Finally, we demonstrate that our methodology is modular and both the ATP-competitive fragment and conjugation chemistry can be swapped.

CLK2 inhibition ameliorates autistic features associated with SHANK3 deficiency

SH3 and multiple ankyrin repeat domains 3 (SHANK3) haploinsufficiency is causative for the neurological features of Phelan-McDermid syndrome (PMDS), including a high risk of autism spectrum disorder (ASD). We used unbiased, quantitative proteomics to identify changes in the phosphoproteome of Shank3-deficient neurons. Down-regulation of protein kinase B (PKB/Akt)-mammalian target of rapamycin complex 1 (mTORC1) signaling resulted from enhanced phosphorylation and activation of serine/threonine protein phosphatase 2A (PP2A) regulatory subunit, B56β, due to increased steady-state levels of its kinase, Cdc2-like kinase 2 (CLK2). Pharmacological and genetic activation of Akt or inhibition of CLK2 relieved synaptic deficits in Shank3-deficient and PMDS patient-derived neurons. CLK2 inhibition also restored normal sociability in a Shank3-deficient mouse model. Our study thereby provides a novel mechanistic and potentially therapeutic understanding of deregulated signaling downstream of Shank3 deficiency.