Cellular functions of stem cell factors mediated by the ubiquitin-proteasome system

Degradation meets development: Implications in β-cell development and diabetes

Pancreatic development is orchestrated by timely synthesis and degradation of stage-specific transcription factors (TFs). The transition from one stage to another stage is dependent on the precise expression of the developmentally relevant TFs. Persistent expression of particular TF would impede the exit from the progenitor stage to the matured cell type. Intracellular protein degradation-mediated protein turnover contributes to a major extent to the turnover of these TFs and thereby dictates the development of different tissues. Since even subtle changes in the crucial cellular pathways would dramatically impact pancreatic β-cell performance, it is generally acknowledged that the biological activity of these pathways is tightly regulated by protein synthesis and degradation process. Intracellular protein degradation is executed majorly by the ubiquitin proteasome system (UPS) and Lysosomal degradation pathway. As more than 90% of the TFs are targeted to proteasomal degradation, this review aims to examine the crucial role of UPS in normal pancreatic β-cell development and how dysfunction of these pathways manifests in metabolic syndromes such as diabetes. Such understanding would facilitate designing a faithful approach to obtain a therapeutic quality of β-cells from stem cells.

The Role of Ubiquitin-Proteasome System in the Biology of Stem Cells

Selective degradation of cellular proteins by the ubiquitin-proteasome system (UPS) is one of the key regulatory mechanisms in eukaryotic cells. A growing body of evidence indicates that UPS is involved in the regulation of fundamental processes in mammalian stem cells, including proliferation, differentiation, cell migration, aging, and programmed cell death, via proteolytic degradation of key transcription factors and cell signaling proteins and post-translational modification of target proteins with ubiquitin. Studying molecular mechanisms of proteostasis in stem cells is of great importance for the development of new therapeutic approaches aimed at the treatment of autoimmune and neurodegenerative diseases, cancer, and other socially significant pathologies. This review discusses current data on the UPS functions in stem cells.

Tespa1 facilitates hematopoietic and leukemic stem cell maintenance by restricting c-Myc degradation

Hematopoietic stem cells (HSCs) and leukemia stem cells (LSCs) have robust self-renewal potential, which is responsible for sustaining normal and malignant hematopoiesis, respectively. Although considerable efforts have been made to explore the regulation of HSC and LSC maintenance, the underlying molecular mechanism remains obscure. Here, we observe that the expression of thymocyte-expressed, positive selection-associated 1 (Tespa1) is markedly increased in HSCs after stresses exposure. Of note, deletion of Tespa1 results in short-term expansion but long-term exhaustion of HSCs in mice under stress conditions due to impaired quiescence. Mechanistically, Tespa1 can interact with CSN subunit 6 (CSN6), a subunit of COP9 signalosome, to prevent ubiquitination-mediated degradation of c-Myc protein in HSCs. As a consequence, forcing c-Myc expression improves the functional defect of Tespa1-null HSCs. On the other hand, Tespa1 is identified to be highly enriched in human acute myeloid leukemia (AML) cells and is essential for AML cell growth. Furthermore, using MLL-AF9-induced AML model, we find that Tespa1 deficiency suppresses leukemogenesis and LSC maintenance. In summary, our findings reveal the important role of Tespa1 in promoting HSC and LSC maintenance and therefore provide new insights on the feasibility of hematopoietic regeneration and AML treatment.

USP25 UPREGULATION BOOSTS GSDMD -MEDIATED PYROPTOSIS OF ACINAR CELLS IN ACUTE PANCREATITIS

ABSTRACT

Acute pancreatitis (AP) is an inflammation-associated disorder in the digestive system. Ubiquitin-specific peptidase 25 ( USP25 ) can modulate inflammation in diseases. This study expounded on the role of USP25 in pyroptosis of acinar cells in AP. Acinar cells were treated with lipopolysaccharide (LPS) and caerulein (CRE) to induce AP. Afterward, the expression patterns of USP25 , microRNA (miR)-10a-5p, and Krüppel-like factor 4 ( KLF4 ) in acinar cells were examined. Then, acinar cell viability and levels of NLR family pyrin-domain containing 3 (NLRP3), cleaved caspase-1, cleaved N -terminal gasdermin D ( GSDMD - N ), interleukin (IL)-1β, and IL-18 were determined. We observed that USP25 was highly expressed in AP models, and silencing USP25 increased cell viability and inhibited pyroptosis of AP acinar cells. The bindings of USP25 to KLF4 and miR-10a-5p to KLF4 and the GSDMD 3'UTR sequence were validated. We found that USP25 binding to KLF4 inhibited ubiquitination degradation of KLF4 , KLF4 transcriptionally decreased miR-10a-5p expression, and miR-10a-5p targeted GSDMD expression. Finally, rescue experiments proved that KLF4 overexpression or miR-10a-5p suppression enhanced pyroptosis of AP acinar cells. Overall, USP25 stabilized KLF4 expression through deubiquitination, limited miR-10a-5p expression, and increased GSDMD expression, finally promoting pyroptosis of acinar cells in AP.

The Pt(S-pr-thiosal)2 and BCL1 Leukemia Lymphoma: Antitumor Activity In Vitro and In Vivo

B cell malignancies are, despite the development of targeted therapy in a certain percentage of the patients still a chronic disease with relapses, requiring multiple lines of therapy. Regimens that include platinum-based drugs provide high response rates in different B cell lymphomas, high-risk chronic lymphocytic leukemia (CLL), and devastating complication of CLL, Richter’s syndrome. The aim of this study was to explore the potential antitumor activity of previously synthetized platinum(IV) complex with alkyl derivatives of thyosalicilc acid, PtCl2(S-pr-thiosal)2, toward murine BCL1 cells and to delineate possible mechanisms of action. The PtCl2(S-pr-thiosal)2 reduced the viability of BCL1 cells in vitro but also reduced the growth of metastases in the leukemia lymphoma model in BALB/c mice. PtCl2(S-pr-thiosal)2 induced apoptosis, inhibited proliferation of BCL1 cells, and induced cell cycle disturbance. Treatment of BCL1 cells with PtCl2(S-pr-thiosal)2 inhibited expression of cyclin D3 and cyclin E and enhanced expression of cyclin-dependent kinase inhibitors p16, p21, and p27 resulting in cell cycle arrest in the G1 phase, reduced the percentage of BCL1 cells in the S phase, and decreased expression of Ki-67. PtCl2(S-pr-thiosal)2 treatment reduced expression of phosphorylated STAT3 and downstream-regulated molecules associated with cancer stemness and proliferation, NANOG, cyclin D3, and c-Myc, and expression of phosphorylated NFκB in vitro and in vivo. In conclusion, PtCl2(S-pr-thiosal)2 reduces STAT3 and NFκB phosphorylation resulting in inhibition of BCL1 cell proliferation and the triggering of apoptotic cell death.

Kap1 Regulates the Stability of Lin28A in Embryonic Stem Cells

Lin28A is an RNA-binding protein that controls mammalian development and maintenance of the pluripotency of embryonic stem cells (ESCs) via regulating the processing of the microRNA let-7. Lin28A is highly expressed in ESCs, and ectopic expression of this protein facilitates reprogramming of somatic cells to induced pluripotent stem cells. However, the mechanisms underlying the post-translational regulation of Lin28A protein stability in ESCs remain unclear. In the present study, we identified Kap1 (KRAB-associated protein 1) as a novel Lin28A-binding protein using affinity purification and mass spectrometry. Kap1 specifically interacted with the N-terminal region of Lin28A through its coiled-coil domain. Kap1 overexpression significantly attenuated Lin28A ubiquitination and increased its stability. However, small interfering RNA-mediated knockdown of Kap1 promoted the ubiquitination of Lin28A, leading to its proteasomal degradation. Trim71, an E3 ubiquitin ligase, induced Lin28A degradation and Kap1 knockdown accelerated the Trim71-dependent degradation of Lin28A. Mutation of the lysine 177 residue of Lin28A to arginine abrogated the ubiquitination and degradation of Lin28A which were accelerated by Kap1 silencing. Moreover, Kap1 overexpression led to the accumulation of Lin28A in the cytoplasm, but not in the nucleus, and reduced the levels of let-7 subtypes. These results suggest that Kap1 plays a key role in regulation of the stability of Lin28A by modulating the Trim71-mediated ubiquitination and subsequent degradation of Lin28A, thus playing a pivotal role in the regulation of ESC self-renewal and pluripotency.

Protein clearance strategies for disease intervention

Protein homeostasis, or proteostasis, is essential for cell function and viability. Unwanted, damaged, misfolded and aggregated proteins are degraded by the ubiquitin–proteasome system (UPS) and the autophagy-lysosome pathway. Growing evidence indicates that alterations in these major proteolytic mechanisms lead to a demise in proteostasis, contributing to the onset and development of distinct diseases. Indeed, dysregulation of the UPS or autophagy is linked to several neurodegenerative, infectious and inflammatory disorders as well as cancer. Thus, modulation of protein clearance pathways is a promising approach for therapeutics. In this review, we discuss recent findings and open questions on how targeting proteolytic mechanisms could be applied for disease intervention.

Effects of deubiquitylases on the biological behaviors of neural stem cells

New neurons are generated throughout life in distinct regions of the mammalian brain due to the proliferation and differentiation of neural stem cells (NSCs). Ubiquitin, a post-translational modification of cellular proteins, is an important factor in regulating neurogenesis. Deubiquitination is a biochemical process that mediates the removal of ubiquitin moieties from ubiquitin-conjugated substrates. Recent studies have provided growing evidence that deubiquitylases (DUBs) which reverse ubiquitylation process play critical roles in NSCs maintenance, differentiation and maturation. This review mainly focused on the relationship of DUBs and NSCs, and further summarized recent advances in our understanding of DUBs on regulating NSCs biological behaviors.

Isolation and Characterization of Human Colon Adenocarcinoma Stem-Like Cells Based on the Endogenous Expression of the Stem Markers

BACKGROUND

Cancer stem cells' (CSCs) self-maintenance is regulated via the pluripotency pathways promoting the most aggressive tumor phenotype. This study aimed to use the activity of these pathways for the CSCs' subpopulation enrichment and separating cells characterized by the OCT4 and SOX2 expression.

METHODS

To select and analyze CSCs, we used the SORE6x lentiviral reporter plasmid for viral transduction of colon adenocarcinoma cells. Additionally, we assessed cell chemoresistance, clonogenic, invasive and migratory activity and the data of mRNA-seq and intrinsic disorder predisposition protein analysis (IDPPA).

RESULTS

We obtained the line of CSC-like cells selected on the basis of the expression of the OCT4 and SOX2 stem cell factors. The enriched CSC-like subpopulation had increased chemoresistance as well as clonogenic and migration activities. The bioinformatic analysis of mRNA seq data identified the up-regulation of pluripotency, development, drug resistance and phototransduction pathways, and the downregulation of pathways related to proliferation, cell cycle, aging, and differentiation. IDPPA indicated that CSC-like cells are predisposed to increased intrinsic protein disorder.

CONCLUSION

The use of the SORE6x reporter construct for CSCs enrichment allows us to obtain CSC-like population that can be used as a model to search for the new prognostic factors and potential therapeutic targets for colon cancer treatment.

Cellular Functions of OCT-3/4 Regulated by Ubiquitination in Proliferating Cells

Octamer-binding transcription factor 3/4 (OCT-3/4), which is involved in the tumorigenesis of somatic cancers, has diverse functions during cancer development. Overexpression of OCT-3/4 has been detected in various human somatic tumors, indicating that OCT-3/4 activation may contribute to the development and progression of cancers. Stem cells can undergo self-renewal, pluripotency, and reprogramming with the help of at least four transcription factors, OCT-3/4, SRY box-containing gene 2 (SOX2), Krüppel-like factor 4 (KLF4), and c-MYC. Of these, OCT-3/4 plays a critical role in maintenance of undifferentiated state of embryonic stem cells (ESCs) and in production of induced pluripotent stem cells (iPSCs). Stem cells can undergo partitioning through mitosis and separate into specific cell types, three embryonic germ layers: the endoderm, the mesoderm, and the trophectoderm. It has been demonstrated that the stability of OCT-3/4 is mediated by the ubiquitin-proteasome system (UPS), which is one of the key cellular mechanisms for cellular homeostasis. The framework of the mechanism is simple, but the proteolytic machinery is complicated. Ubiquitination promotes protein degradation, and ubiquitination of OCT-3/4 leads to regulation of cellular proliferation and differentiation. Therefore, it is expected that OCT-3/4 may play a key role in proliferation and differentiation of proliferating cells.

CRL4-Cereblon complex in Thalidomide Embryopathy: a translational investigation

The Cereblon-CRL4 complex has been studied predominantly with regards to thalidomide treatment of multiple myeloma. Nevertheless, the role of Cereblon-CRL4 in Thalidomide Embryopathy (TE) is still not understood. Not all embryos exposed to thalidomide develop TE, hence here we evaluate the role of the CRL4-Cereblon complex in TE variability and susceptibility. We sequenced CRBN, DDB1, CUL4A, IKZF1, and IKZF3 in individuals with TE. To better interpret the variants, we suggested a score and a heatmap comprising their regulatory effect. Differential gene expression after thalidomide exposure and conservation of the CRL4-Cereblon protein complex were accessed from public repositories. Results suggest a summation effect of Cereblon variants on pre-axial longitudinal limb anomalies, and heatmap scores identify the CUL4A variant rs138961957 as potentially having an effect on TE susceptibility. CRL4-Cereblon gene expression after thalidomide exposure and CLR4-Cereblon protein conservation does not explain the difference in Thalidomide sensitivity between species. In conclusion, we suggest that CRL4-Cereblon variants act through several regulatory mechanisms, which may influence CRL4-Cereblon complex assembly and its ability to bind thalidomide. Human genetic variability must be addressed not only to further understand the susceptibility to TE, but as a crucial element in therapeutics, including in the development of pharmacogenomics strategies.

Deubiquitinase inhibitor degrasyn suppresses metastasis by targeting USP5-WT1-E-cadherin signalling pathway in pancreatic ductal adenocarcinoma

Wilm's tumour-1 (WT1) is overexpressed in pancreatic ductal adenocarcinoma (PDAC) and enhances metastasis. Deubiquitination stabilizes target proteins, and inhibiting deubiquitination facilitates the degradation of target proteins. However, whether inhibiting deubiquitination of WT1 facilitates its degradation and presents anti-cancer ability in PDAC is unknown. Here, we found that deubiquitinase inhibitor degrasyn rapidly induced the degradation of endogenous and exogenous WT1 through enhancing ubiquitination of WT1 followed by the up-regulation of E-cadherin. Knockdown of WT1 by short hairpin RNAs (shRNAs) inhibited metastasis and overexpression of WT1 partially prevented degrasyn-induced anti-metastasis activity, suggesting that degrasyn presents anti-metastasis activity partially through degrading WT1 protein. We further identified that USP5 deubiquitinated WT1 and stabilized its expression. The higher expressions of USP5 and WT1 are associated with tumour metastasis. More importantly, degrasyn inhibited the activity of USP5 and overexpression of USP5 partially prevented degrasyn-induced degradation of WT1 protein, suggesting that degrasyn degraded WT1 protein through inhibiting the activity of USP5. Finally, degrasyn reduced the tumorigenicity in a xenograft mouse model and reduced the metastasis in vivo. Our results indicate that degrasyn presents strong anti-cancer activity through USP5-WT1-E-cadherin signalling in PDAC. Therefore, degrasyn holds promise as cancer therapeutic agent in PDAC with high expressions of USP5 and WT1.

The function and regulation of OTU deubiquitinases

Post-translational modification of cellular proteins by ubiquitin regulates numerous cellular processes, including cell division, immune responses, and apoptosis. Ubiquitin-mediated control over these processes can be reversed by deubiquitinases (DUBs), which remove ubiquitin from target proteins and depolymerize polyubiquitin chains. Recently, much progress has been made in the DUBs. In humans, the ovarian tumor protease (OTU) subfamily of DUBs includes 16 members, most of which mediate cell signaling cascades. These OTUs show great variation in structure and function, which display a series of mechanistic features. In this review, we provide a comprehensive analysis of current progress in character, structure and function of OTUs, such as the substrate specificity and catalytic activity regulation. Then we discuss the relationship between some diseases and OTUs. Finally, we summarize the structure of viral OTUs and their function in immune escape and viral survival. Despite the challenges, OTUs might provide new therapeutic targets, due to their involvement in key regulatory processes.

Purinergic Signaling Pathway in Human Olfactory Neuronal Precursor Cells

Extracellular ATP and trophic factors released by exocytosis modulate in vivo proliferation, migration, and differentiation in multipotent stem cells (MpSC); however, the purinoceptors mediating this signaling remain uncharacterized in stem cells derived from the human olfactory epithelium (hOE). Our aim was to determine the purinergic pathway in isolated human olfactory neuronal precursor cells (hONPC) that exhibit MpSC features. Cloning by limiting dilution from a hOE heterogeneous primary culture was performed to obtain a culture predominantly constituted by hONPC. Effectiveness of cloning to isolate MpSC-like precursors was corroborated through immunodetection of specific protein markers and by functional criteria such as self-renewal, proliferation capability, and excitability of differentiated progeny. P2 receptor expression in hONPC was determined by Western blot, and the role of these purinoceptors in the ATP-induced exocytosis and changes in cytosolic Ca²⁺ ([Ca²⁺]_i) were evaluated using the fluorescent indicators FM1-43 and Fura-2 AM, respectively. The clonal culture was enriched with SOX2 and OCT3/4 transcription factors; additionally, the proportion of nestin-immunopositive cells, the proliferation capability, and functionality of differentiated progeny remained unaltered through the long-term clonal culture. hONPC expressed P2X receptor subtypes 1, 3-5, and 7, as well as P2Y2, 4, 6, and 11; ATP induced both exocytosis and a transient [Ca²⁺]_i increase predominantly by activation of metabotropic P2Y receptors. Results demonstrated for the first time that ex vivo-expressed functional P2 receptors in MpSC-like hONPC regulate exocytosis and Ca²⁺ signaling. This purinergic-triggered release of biochemical messengers to the extracellular milieu might be involved in the paracrine signaling among hOE cells.

When nature's robots go rogue: exploring protein homeostasis dysfunction and the implications for understanding human aging disease pathologies

INTRODUCTION

Proteins have been historically regarded as 'nature's robots': Molecular machines that are essential to cellular/extracellular physical mechanical properties and catalyze key reactions for cell/system viability. However, these robots are kept in check by other protein-based machinery to preserve proteome integrity and stability. During aging, protein homeostasis is challenged by oxidation, decreased synthesis, and increasingly inefficient mechanisms responsible for repairing or degrading damaged proteins. In addition, disruptions to protein homeostasis are hallmarks of many neurodegenerative diseases and diseases disproportionately affecting the elderly. Areas covered: Here we summarize age- and disease-related changes to the protein machinery responsible for preserving proteostasis and describe how both aging and disease can each exacerbate damage initiated by the other. We focus on alteration of proteostasis as an etiological or phenomenological factor in neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, along with Down syndrome, ophthalmic pathologies, and cancer. Expert commentary: Understanding the mechanisms of proteostasis and their dysregulation in health and disease will represent an essential breakthrough in the treatment of many (senescence-associated) pathologies. Strides in this field are currently underway and largely attributable to the introduction of high-throughput omics technologies and their combination with novel approaches to explore structural and cross-link biochemistry.