Identification of HN252 as a potent inhibitor of protein phosphatase PPM1B

Phosphatase, Mg2+/Mn2+ dependent 1B regulates the hematopoietic stem cells homeostasis via the Wnt/β-catenin signaling

Hematopoietic stem cells (HSC) are primarily dormant in a cell-cycle quiescence state to preserve their self-renewal capacity and long-term maintenance. How HSC maintain the balance between activation and quiescence remains largely unknown. Herein, we found that phosphatase, Mg2+/Mn2+ dependent 1B (Ppm1b) is required for the expansion of phenotypic HSC in vitro. By using a conditional knockout mouse model in which Ppm1b was specifically depleted in hematopoietic cells, we demonstrated that loss of Ppm1b impaired the HSC homeostasis and hematopoietic reconstitution. Ppm1b deficiency mice also exhibited B-cell leukocytopenia, which is due to the compromised commitment and proliferation of B-biased lymphoid progenitor cells from common lymphoid progenitors. With the aid of a small molecular inhibitor, we confirmed the roles of Ppm1b in adult hematopoiesis that phenocopied the effects with loss of Ppm1b. Furthermore, transcriptome profiling of Ppm1b-deficient HSC revealed the disruptive quiescence of HSC. Mechanistically, Ppm1b interacted with β-catenin and mediated its dephosphorylation. Loss of Ppm1b led to the decrease in the active β-catenin (non-phosphorylated) that interrupted the Wnt/β-catenin signaling in HSC, which consequently suppressed HSC expansion. Together, our study identified an indispensable role for Ppm1b in regulating HSC homeostasis via the Wnt/β-catenin pathway.

Hematopoietic stem cell fate under the influence of Ser/Thr protein phosphatases

Not available.

A comprehensive overview of PPM1B: From biological functions to diseases

Reversible phosphorylation of proteins is an important mechanism that regulates cellular processes, which are precisely regulated by protein kinases and phosphatases. PPM1B is a metal ion-dependent serine/threonine protein phosphatase, which regulates multiple biological functions by targeting substrate dephosphorylation, such as cell cycle, energy metabolism, inflammatory responses. In this review, we summarized the occurrent understandings of PPM1B focused on its regulation of signaling pathways, related diseases, and small-molecular inhibitors, which may provide new insights for the identification of PPM1B inhibitors and the treatment of PPM1B-related diseases.

Lysine crotonylation regulates leucine-deprivation-induced autophagy by a 14-3-3ε-PPM1B axis

Lysine crotonylation as a protein post-translational modification regulates diverse cellular processes and functions. However, the role of crotonylation in nutrient signaling pathways remains unclear. Here, we find a positive correlation between global crotonylation levels and leucine-deprivation-induced autophagy. Crotonylome profiling identifies many crotonylated proteins regulated by leucine deprivation. Bioinformatics analysis dominates 14-3-3 proteins in leucine-mediated crotonylome. Expression of 14-3-3ε crotonylation-deficient mutant significantly inhibits leucine-deprivation-induced autophagy. Molecular dynamics analysis shows that crotonylation increases molecular instability and disrupts the 14-3-3ε amphipathic pocket through which 14-3-3ε interacts with binding partners. Leucine-deprivation-induced 14-3-3ε crotonylation leads to the release of protein phosphatase 1B (PPM1B) from 14-3-3ε interaction. Active PPM1B dephosphorylates ULK1 and subsequently initiates autophagy. We further find that 14-3-3ε crotonylation is regulated by HDAC7. Taken together, our findings demonstrate that the 14-3-3ε-PPM1B axis regulated by crotonylation may play a vital role in leucine-deprivation-induced autophagy.

Binding of Vialinin A and p-Terphenyl Derivatives to Ubiquitin-Specific Protease 4 (USP4): A Molecular Docking Study

The para-terphenyl derivative vialinin A (Vi-A), isolated from Thelephora fungi, has been characterized as a potent inhibitor of the ubiquitin-specific protease 4 (USP4). Blockade of USP4 contributes to the anti-inflammatory and anticancer properties of the natural product. We have investigated the interaction of Vi-A with USP4 by molecular modeling, to locate the binding site (around residue V98 within the domain in USP segment) and to identify the binding process and interaction contacts. From this model, a series of 32 p-terphenyl compounds were tested as potential USP4 binders, mainly in the vialinin, terrestrin and telephantin series. We identified 11 compounds presenting a satisfactory USP4 binding capacity, including two fungal products, vialinin B and aurantiotinin A, with a more favorable empirical energy of USP4 interaction (ΔE) than the reference product Vi-A. The rare p-terphenyl aurantiotinin A, isolated from the basidiomycete T. aurantiotincta, emerged as a remarkable USP4 binder. Structure-binding relationships have been identified and discussed, to guide the future design of USP4 inhibitors based on the p-terphenyl skeleton. The docking study should help the identification of other protease inhibitors from fungus.

Discovery of N-arylcinnamamides as novel erythroblast enucleation inducers

Derivation of mature red blood cells (RBCs) from stem cells in vitro is a promising solution to the current shortage of blood supply, in which terminal enucleation is the rate-limiting step. Here we discovered two cinnamamides B8 and B16 showed potential activities of enhancing the enucleation of erythroblasts through the screening of "in-house" compound library. Subsequently, twenty-four N-arylcinnamamides were rationally designed and synthesized on the basis of the structure of B8 and B16, in which N-(9H-carbazol-2-yl)cinnamamide (KS-2) significantly elevated the percentage of reticulocytes in the cultured mouse fetal liver cells in vitro (relative enucleation = 2.43). The underlying mechanism of KS-2 in promoting mouse erythroid enucleation is accelerating the process of cell cycle exit via p53 activation in late stage erythrocytes. These results strongly suggest that compound KS-2 is worthy of further study as a potential erythrocyte enucleation inducer.

Anti-inflammatory and anticancer p-terphenyl derivatives from fungi of the genus Thelephora

Fungi from the genus Thelephora have been exploited to identify bioactive compounds. The main natural products characterized are para-terphenyl derivatives, chiefly represented by the lead anti-inflammatory compound vialinin A isolated from species T. vialis and T. terrestris. Different series of p-terphenyls have been identified, including vialinins, ganbajunins, terrestrins, telephantins and other products. Their mechanism of action is not always clearly identified, and different potential molecule targets have been proposed. The lead vialinin A functions as a protease inhibitor, efficiently targeting ubiquitin-specific peptidases USP4/5 and sentrin-specific protease SENP1 which are prominent anti-inflammatory and anticancer targets. Protease inhibition is coupled with a powerful inhibition of the cellular production of tumor necrosis factor TNFα. Other mechanisms contributing to the anti-inflammatory or anti-proliferative action of these p-terphenyl compounds have been invoked, including the formation of cytotoxic copper complexes for derivatives bearing a catechol central unit such vialinin A, terrestrin B and telephantin O. These p-terphenyl compounds could be further exploited to design novel anticancer agents, as evidenced with the parent compound terphenyllin (essentially found in Aspergillus species) which has revealed marked antitumor and anti-metastatic effects in xenograft models of gastric and pancreatic cancer. This review shed light on the structural and functional diversity of p-terphenyls compounds isolated from Thelephora species, their molecular targets and pharmacological properties.

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.