Xiangshu Xiao

Bio: Xiangshu Xiao is an academic researcher from Oregon Health & Science University. The author has contributed to research in topics: Protein–protein interaction & Small molecule. The author has an hindex of 1, co-authored 1 publications receiving 57 citations.

Discovery of a small-molecule inhibitor of the KIX-KID interaction.

Abstract: Protein–protein interactions are essential for transmitting signals from extracellular space to cell nuclei and also for cell–cell communication. Small molecules that target protein–protein interactions, therefore, are great research tools for dissecting the biological functions of a given protein–protein interaction and potential therapeutics for many different human diseases.[1] However, targeting protein–protein interactions by small molecules remains a significant challenge.[1, 2]

Protein lysine acetylation by p300/CBP.

Abstract: Since their discovery in the 1980s and 1990s, the human protein lysine acetyltransferase encoded by the paralogous p300 and CBP genes has received much interest. p300/CBP functions in regulating the expression of genes controlling several basic cellular processes, such as proliferation and homeostasis, and plays a role in a variety of human diseases, particularly solid tumors. Numerous natural product and synthetic inhibitors of the acetyltransferase activity have been identified and used to generate a crystal structure of the active site, probe the p300/CBP enzyme kinetics, and interrogate p300/CBP cellular functions. These studies revealed that acetyl-CoA binds in a tunnel enclosed by a unique loop, while the substrate protein transiently associates with an acidic patch, following a hit-and-run kinetic mechanism. p300/CBP acetylates histones as well as other proteins including other epigenetic enzymes and transcription factors. Studies with inhibitor compounds in cells and animals have confirmed that the p300/CBP acetylation activity has roles in diverse functions including cell migration and invasion, maintenance of the differentiated state, tau-mediated neurodegeneration, and learning and memory. Also, important components of p300/CBP are the domains flanking the acetyltransferase domain, including three cysteine/histidine-rich domains and a bromodomain. Protein ligands of these have been identified. Their roles in regulating the acetyltransferase activity and substrate specificity, as well as identification of compounds that can block or mimic ligand binding, are topics of ongoing study. Biochemical investigation of protein acetylation has posed unique challenges, due in part to its dynamic reversibility, the weak affinity of binding modules that recognize it, and the complexity of the multiprotein interaction networks. Therefore, diverse techniques in biochemistry, molecular biology, and proteomics have coevolved with our understanding of the p300/CBP enzyme. In this Review, part of the thematic issue on Epigenetics, we summarize the current understanding of p300/CBP including the novel technologies developed for these studies.

Transcriptional/epigenetic regulator CBP/p300 in tumorigenesis: structural and functional versatility in target recognition.

Abstract: In eukaryotic cells, gene transcription is regulated by sequence-specific DNA-binding transcription factors that recognize promoter and enhancer elements near the transcriptional start site. Some coactivators promote transcription by connecting transcription factors to the basal transcriptional machinery. The highly conserved coactivators CREB-binding protein (CBP) and its paralog, E1A-binding protein (p300), each have four separate transactivation domains (TADs) that interact with the TADs of a number of DNA-binding transcription activators as well as general transcription factors (GTFs), thus mediating recruitment of basal transcription machinery to the promoter. Most promoters comprise multiple activator-binding sites, and many activators contain tandem TADs, thus multivalent interactions may stabilize CBP/p300 at the promoter, and intrinsically disordered regions in CBP/p300 and many activators may confer adaptability to these multivalent complexes. CBP/p300 contains a catalytic histone acetyltransferase (HAT) domain, which remodels chromatin to ‘relax’ its superstructure and enables transcription of proximal genes. The HAT activity of CBP/p300 also acetylates some transcription factors (e.g., p53), hence modulating the function of key transcriptional regulators. Through these numerous interactions, CBP/p300 has been implicated in complex physiological and pathological processes, and, in response to different signals, can drive cells towards proliferation or apoptosis. Dysregulation of the transcriptional and epigenetic functions of CBP/p300 is associated with leukemia and other types of cancer, thus it has been recognized as a potential anti-cancer drug target. In this review, we focus on recent exciting findings in the structural mechanisms of CBP/p300 involving multivalent and dynamic interactions with binding partners, which may pave new avenues for anti-cancer drug development.

Targeting CREB for cancer therapy: friend or foe.

Abstract: The cyclic-AMP response element-binding protein (CREB) is a nuclear transcription factor activated by phosphorylation at Ser133 by multiple serine/threonine (Ser/Thr) kinases. Upon phosphorylation, CREB binds the transcriptional co-activator, CBP (CREB-binding protein), to initiate CREB-dependent gene transcription. CREB is a critical regulator of cell differentiation, proliferation and survival in the nervous system. Recent studies have shown that CREB is involved tumor initiation, progression and metastasis, supporting its role as a proto-oncogene. Overexpression and over-activation of CREB were observed in cancer tissues from patients with prostate cancer, breast cancer, non-small-cell lung cancer and acute leukemia while down-regulation of CREB in several distinct cancer cell lines resulted in inhibition of cell proliferation and induction of apoptosis, suggesting that CREB may be a promising target for cancer therapy. Although CREB, as a transcription factor, is a challenging target for small molecules, various small molecules have been discovered to inhibit CREB phosphorylation, CREB-DNA, or CREB-CBP interaction. These results suggest that CREB is a suitable transcription factor for drug targeting and therefore targeting CREB could represent a novel strategy for cancer therapy.

CREB Family Transcription Factors Are Major Mediators of BDNF Transcriptional Autoregulation in Cortical Neurons

Abstract: BDNF signaling via its transmembrane receptor TrkB has an important role in neuronal survival, differentiation, and synaptic plasticity. Remarkably, BDNF is capable of modulating its own expression levels in neurons, forming a transcriptional positive feedback loop. In the current study, we have investigated this phenomenon in primary cultures of rat cortical neurons using overexpression of dominant-negative forms of several transcription factors, including CREB, ATF2, C/EBP, USF, and NFAT. We show that CREB family transcription factors, together with the coactivator CBP/p300, but not the CRTC family, are the main regulators of rat BDNF gene expression after TrkB signaling. CREB family transcription factors are required for the early induction of all the major BDNF transcripts, whereas CREB itself directly binds only to BDNF promoter IV, is phosphorylated in response to BDNF-TrkB signaling, and activates transcription from BDNF promoter IV by recruiting CBP. Our complementary reporter assays with BDNF promoter constructs indicate that the regulation of BDNF by CREB family after BDNF-TrkB signaling is generally conserved between rat and human. However, we demonstrate that a nonconserved functional cAMP-responsive element in BDNF promoter IXa in humans renders the human promoter responsive to BDNF-TrkB-CREB signaling, whereas the rat ortholog is unresponsive. Finally, we show that extensive BDNF transcriptional autoregulation, encompassing all major BDNF transcripts, occurs also in vivo in the adult rat hippocampus during BDNF-induced LTP. Collectively, these results improve the understanding of the intricate mechanism of BDNF transcriptional autoregulation.SIGNIFICANCE STATEMENT Deeper understanding of stimulus-specific regulation of BDNF gene expression is essential to precisely adjust BDNF levels that are dysregulated in various neurological disorders. Here, we have elucidated the molecular mechanisms behind TrkB signaling-dependent BDNF mRNA induction and show that CREB family transcription factors are the main regulators of BDNF gene expression after TrkB signaling. Our results suggest that BDNF-TrkB signaling may induce BDNF gene expression in a distinct manner compared with neuronal activity. Moreover, our data suggest the existence of a stimulus-specific distal enhancer modulating BDNF gene expression.

Identification of a Potent Inhibitor of CREB-Mediated Gene Transcription with Efficacious in Vivo Anticancer Activity

Abstract: Recent studies have shown that nuclear transcription factor cyclic adenosine monophosphate response element binding protein (CREB) is overexpressed in many different types of cancers. Therefore, CREB has been pursued as a novel cancer therapeutic target. Naphthol AS-E and its closely related derivatives have been shown to inhibit CREB-mediated gene transcription and cancer cell growth. Previously, we identified naphthamide 3a as a different chemotype to inhibit CREB’s transcription activity. In a continuing effort to discover more potent CREB inhibitors, a series of structural congeners of 3a was designed and synthesized. Biological evaluations of these compounds uncovered compound 3i (666-15) as a potent and selective inhibitor of CREB-mediated gene transcription (IC50 = 0.081 ± 0.04 μM). 666-15 also potently inhibited cancer cell growth without harming normal cells. In an in vivo MDA-MB-468 xenograft model, 666-15 completely suppressed the tumor growth without overt toxicity. These results further suppo...