PTENα, a PTEN isoform translated through alternative initiation, regulates mitochondrial function and energy metabolism

High glucose-induced downregulation of PTEN-Long is sufficient for proximal tubular cell injury in diabetic kidney disease

During the progression of diabetic kidney disease, proximal tubular epithelial cells respond to high glucose to induce hypertrophy and matrix expansion leading to renal fibrosis. Recently, a non-canonical PTEN has been shown to be translated from an upstream initiation codon CUG (leucine) to produce a longer protein called PTEN-Long (PTEN-L). Interestingly, the extended sequence present in PTEN-L contains cell secretion/penetration signal. Role of this non-canonical PTEN-L in diabetic renal tubular injury is not known. We show that high glucose decreases expression of PTEN-L. As a mechanism of its function, we find that reduced PTEN-L activates Akt-2, which phosphorylates and inactivate tuberin and PRAS40, resulting in activation of mTORC1 in tubular cells. Antibacterial agent acriflavine and antiviral agent ATA regulate translation from CUG codon. Acriflavine and ATA, respectively, decreased and increased expression of PTEN-L to altering Akt-2 and mTORC1 activation in the absence of change in expression of canonical PTEN. Consequently, acriflavine and ATA modulated high glucose-induced tubular cell hypertrophy and lamininγ1 expression. Importantly, expression of PTEN-L inhibited high glucose-stimulated Akt/mTORC1 activity to abrogate these processes. Since PTEN-L contains secretion/penetration signals, addition of conditioned medium containing PTEN-L blocked Akt-2/mTORC1 activity. Notably, in renal cortex of diabetic mice, we found reduced PTEN-L concomitant with Akt-2/mTORC1 activation, leading to renal hypertrophy and lamininγ1 expression. These results present first evidence for involvement of PTEN-L in diabetic kidney disease.

The Role of Ubiquitination and the E3 Ligase Nedd4 in Regulating Corneal Epithelial Wound Healing

Purpose

Ubiquitination serves as a fundamental post-translational modification in numerous cellular events. Yet, its role in regulating corneal epithelial wound healing (CEWH) remains elusive. This study endeavored to determine the function and mechanism of ubiquitination in CEWH.

Methods

Western blot and immunoprecipitation were used to discern ubiquitination alterations during CEWH in mice. Interventions, including neuronally expressed developmentally downregulated 4 (Nedd4) siRNA and proteasome/lysosome inhibitor, assessed their impact on CEWH. In vitro analyses, such as the scratch wound assay, MTS assay, and EdU staining, were conducted to gauge cell migration and proliferation in human corneal epithelial cells (HCECs). Moreover, transfection of miR-30/200 coupled with a luciferase activity assay ascertained their regulatory mechanism on Nedd4.

Results

Global ubiquitination levels were markedly increased during the mouse CEWH. Importantly, the application of either proteasomal or lysosomal inhibitors notably impeded the healing process both in vivo and in vitro. Furthermore, Nedd4 was identified as an essential E3 ligase for CEWH. Nedd4 expression was significantly upregulated during CEWH. In vivo studies revealed that downregulation of Nedd4 substantially delayed CEWH, whereas further investigations underscored its role in regulating cell proliferation and migration, through the Stat3 pathway by targeting phosphatase and tensin homolog (PTEN). Notably, our findings pinpointed miR-30/200 family members as direct regulators of Nedd4.

Conclusions

Ubiquitination holds pivotal significance in orchestrating CEWH. The critical E3 ligase Nedd4, under the regulatory purview of miR-30 and miR-200, facilitates CEWH through PTEN-mediated Stat3 signaling. This revelation sheds light on a prospective therapeutic target within the realm of CEWH.

RNA-binding protein PTENα blocks RIG-I activation to prevent viral inflammation

A timely inflammatory response is crucial for early viral defense, but uncontrolled inflammation harms the host. Retinoic acid-inducible gene I (RIG-I) has a pivotal role in detecting RNA viruses, yet the regulatory mechanisms governing its sensitivity remain elusive. Here we identify PTENα, an N-terminally extended form of PTEN, as an RNA-binding protein with a preference for the CAUC(G/U)UCAU motif. Using both in vivo and in vitro viral infection assays, we demonstrated that PTENα restricted the host innate immune response, relying on its RNA-binding capacity and phosphatase activity. Mechanistically, PTENα directly bound to viral RNA and enzymatically converted its 5'-triphosphate to 5'-monophosphate, thereby reducing RIG-I sensitivity. Physiologically, brain-intrinsic PTENα exerted protective effects against viral inflammation, while peripheral PTENα restricted host antiviral immunity and, to some extent, promoted viral replication. Collectively, our findings underscore the significance of PTENα in modulating viral RNA- and RIG-I-mediated immune recognition, offering potential therapeutic implications for infectious diseases.

The NTE domain of PTENα/β promotes cancer progression by interacting with WDR5 via its SSSRRSS motif

PTENα/β, two variants of PTEN, play a key role in promoting tumor growth by interacting with WDR5 through their N-terminal extensions (NTEs). This interaction facilitates the recruitment of the SET1/MLL methyltransferase complex, resulting in histone H3K4 trimethylation and upregulation of oncogenes such as NOTCH3, which in turn promotes tumor growth. However, the molecular mechanism underlying this interaction has remained elusive. In this study, we determined the first crystal structure of PTENα-NTE in complex with WDR5, which reveals that PTENα utilizes a unique binding motif of a sequence SSSRRSS found in the NTE domain of PTENα/β to specifically bind to the WIN site of WDR5. Disruption of this interaction significantly impedes cell proliferation and tumor growth, highlighting the potential of the WIN site inhibitors of WDR5 as a way of therapeutic intervention of the PTENα/β associated cancers. These findings not only shed light on the important role of the PTENα/β-WDR5 interaction in carcinogenesis, but also present a promising avenue for developing cancer treatments that target this pathway.

CircPTEN-MT from PTEN regulates mitochondrial energy metabolism

Phosphatase and tensin homolog (PTEN) is a multifunctional gene involved in a variety of physiological and pathological processes. Circular RNAs (circRNAs) are generated from back-splicing events during mRNA processing and participate in cell biological processes through binding to RNAs or proteins. However, PTEN-related circRNAs are largely unknown. Here, we report that circPTEN- mitochondria (MT) (hsa_circ_0002934) is a circular RNA encoded by exons 3, 4, and 5 of PTEN and is a critical regulator of mitochondrial energy metabolism. CircPTEN-MT is localized to mitochondria and physically associated with leucine-rich pentatricopeptide repeat-containing protein (LRPPRC), which regulates posttranscriptional gene expression in mitochondria. Knocking down circPTEN-MT reduces the interaction of LRPPRC and steroid receptor RNA activator (SRA) stem-loop interacting RNA binding protein (SLIRP) and inhibits the polyadenylation of mitochondrial mRNA, which decreases the mRNA level of the mitochondrial complex I subunit and reduces mitochondrial membrane potential and adenosine triphosphate production. Our data demonstrate that circPTEN-MT is an important regulator of cellular energy metabolism. This study expands our understanding of the role of PTEN, which produces both linear and circular RNAs with different and independent functions.

PTEN: an emerging target in rheumatoid arthritis?

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a critical tumor suppressor protein that regulates various biological processes such as cell proliferation, apoptosis, and inflammatory responses by controlling the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PI3K/AKT) signaling pathway. PTEN plays a crucial role in the pathogenesis of rheumatoid arthritis (RA). Loss of PTEN may contribute to survival, proliferation, and pro-inflammatory cytokine release of fibroblast-like synoviocytes (FLS). Also, persistent PI3K signaling increases myeloid cells' osteoclastic potential, enhancing localized bone destruction. Recent studies have shown that the expression of PTEN protein in the synovial lining of RA patients with aggressive FLS is minimal. Experimental upregulation of PTEN protein expression could reduce the damage caused by RA. Nonetheless, a complete comprehension of aberrant PTEN drives RA progression and its interactions with other crucial molecules remains elusive. This review is dedicated to promoting a thorough understanding of the signaling mechanisms of aberrant PTEN in RA and aims to furnish pertinent theoretical support for forthcoming endeavors in both basic and clinical research within this domain.

A vertebrate Vangl2 translational variant required for planar cell polarity

First described in the milkweed bug Oncopeltus fasciatus, planar cell polarity (PCP) is a developmental process essential for embryogenesis and development of polarized structures in Metazoans. This signaling pathway involves a set of evolutionarily conserved genes encoding transmembrane (Vangl, Frizzled, Celsr) and cytoplasmic (Prickle, Dishevelled) molecules. Vangl2 is of major importance in embryonic development as illustrated by its pivotal role during neural tube closure in human, mouse, Xenopus, and zebrafish embryos. Here, we report on the molecular and functional characterization of a Vangl2 isoform, Vangl2-Long, containing an N-terminal extension of about 50 aa, which arises from an alternative near-cognate AUA translation initiation site, lying upstream of the conventional start codon. While missing in Vangl1 paralogs and in all invertebrates, including Drosophila, this N-terminal extension is conserved in all vertebrate Vangl2 sequences. We show that Vangl2-Long belongs to a multimeric complex with Vangl1 and Vangl2. Using morpholino oligonucleotides to specifically knockdown Vangl2-Long in Xenopus, we found that this isoform is functional and required for embryo extension and neural tube closure. Furthermore, both Vangl2 and Vangl2-Long must be correctly expressed for the polarized distribution of the PCP molecules Pk2 and Dvl1 and for centriole rotational polarity in ciliated epidermal cells. Altogether, our study suggests that Vangl2-Long significantly contributes to the pool of Vangl2 molecules present at the plasma membrane to maintain PCP in vertebrate tissues.

To initiate or not to initiate: A critical assessment of eIF2A, eIF2D, and MCT-1·DENR to deliver initiator tRNA to ribosomes

Selection of the correct start codon is critical for high-fidelity protein synthesis. In eukaryotes, this is typically governed by a multitude of initiation factors (eIFs), including eIF2·GTP that directly delivers the initiator tRNA (Met-tRNAi Met ) to the P site of the ribosome. However, numerous reports, some dating back to the early 1970s, have described other initiation factors having high affinity for the initiator tRNA and the ability of delivering it to the ribosome, which has provided a foundation for further work demonstrating non-canonical initiation mechanisms using alternative initiation factors. Here we provide a critical analysis of current understanding of eIF2A, eIF2D, and the MCT-1·DENR dimer, the evidence surrounding their ability to initiate translation, their implications in human disease, and lay out important key questions for the field. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes Translation > Mechanisms Translation > Regulation.

Yeast eIF2A has a minimal role in translation initiation and uORF-mediated translational control in vivo

Initiating translation of most eukaryotic mRNAs depends on recruitment of methionyl initiator tRNA (Met-tRNAi) in a ternary complex (TC) with GTP-bound eukaryotic initiation factor 2 (eIF2) to the small (40S) ribosomal subunit, forming a 43S preinitiation complex (PIC) that attaches to the mRNA and scans the 5'-untranslated region (5' UTR) for an AUG start codon. Previous studies have implicated mammalian eIF2A in GTP-independent binding of Met-tRNAi to the 40S subunit and its recruitment to specialized mRNAs that do not require scanning, and in initiation at non-AUG start codons, when eIF2 function is attenuated by phosphorylation of its α-subunit during stress. The role of eIF2A in translation in vivo is poorly understood however, and it was unknown whether the conserved ortholog in budding yeast can functionally substitute for eIF2. We performed ribosome profiling of a yeast deletion mutant lacking eIF2A and isogenic wild-type (WT) cells in the presence or absence of eIF2α phosphorylation induced by starvation for amino acids isoleucine and valine. Whereas starvation of WT confers changes in translational efficiencies (TEs) of hundreds of mRNAs, the eIF2AΔ mutation conferred no significant TE reductions for any mRNAs in non-starved cells, and it reduced the TEs of only a small number of transcripts in starved cells containing phosphorylated eIF2α. We found no evidence that eliminating eIF2A altered the translation of mRNAs containing putative internal ribosome entry site (IRES) elements, or harboring uORFs initiated by AUG or near-cognate start codons, in non-starved or starved cells. Thus, very few mRNAs (possibly only one) appear to employ eIF2A for Met-tRNAi recruitment in yeast cells, even when eIF2 function is attenuated by stress.

Unraveling the Concealed Transcriptomic Landscape of PTEN in Human Malignancies

Background

Phosphatase and tensin homolog, widely known as PTEN, is a major negative regulator of the PI3K/AKT/mTOR signaling pathway, involved in the regulation of a variety of important cellular processes, including cell proliferation, growth, survival, and metabolism. Since most of the molecules involved in this biological pathway have been described as key regulators in cancer, the study of the corresponding genes at several levels is crucial.

Objective

Although previous studies have elucidated the physiological role of PTEN under normal conditions and its involvement in carcinogenesis and cancer progression, the transcriptional profile of PTEN has been poorly investigated.

Methods

In this study, instead of conducting the "gold-standard" direct RNA sequencing that fails to detect less abundant novel mRNAs due to the decreased sequencing depth, we designed and implemented a multiplexed PTEN-targeted sequencing approach that combined both short- and long-read sequencing.

Results

Our study has highlighted a broad spectrum of previously unknown PTEN mRNA transcripts and assessed their expression patterns in a wide range of human cancer and non-cancer cell lines, shedding light on the involvement of PTEN in cell cycle dysregulation and thus tumor development.

Conclusion

The identification of the described novel PTEN splice variants could have significant implications for understanding PTEN regulation and function, and provide new insights into PTEN biology, opening new avenues for monitoring PTEN-related diseases, including cancer.

Yeast eIF2A has a minimal role in translation initiation and uORF-mediated translational control in vivo

Initiating translation of most eukaryotic mRNAs depends on recruitment of methionyl initiator tRNA (Met-tRNAi) in a ternary complex (TC) with GTP-bound eukaryotic initiation factor 2 (eIF2) to the small (40S) ribosomal subunit, forming a 43S preinitiation complex (PIC) that attaches to the mRNA and scans the 5'-untranslated region (5' UTR) for an AUG start codon. Previous studies have implicated mammalian eIF2A in GTP-independent binding of Met-tRNAi to the 40S subunit and its recruitment to specialized mRNAs that do not require scanning, and in initiation at non-AUG start codons, when eIF2 function is attenuated by phosphorylation of its α-subunit during stress. The role of eIF2A in translation in vivo is poorly understood however, and it was unknown whether the conserved ortholog in budding yeast can functionally substitute for eIF2. We performed ribosome profiling of a yeast deletion mutant lacking eIF2A and isogenic wild-type (WT) cells in the presence or absence of eIF2α phosphorylation induced by starvation for amino acids isoleucine and valine. Whereas starvation of WT confers changes in translational efficiencies (TEs) of hundreds of mRNAs, the eIF2AΔ mutation conferred no significant TE reductions for any mRNAs in non-starved cells, and it reduced the TEs of only a small number of transcripts in starved cells containing phosphorylated eIF2α. We found no evidence that eliminating eIF2A altered the translation of mRNAs containing putative IRES elements, or harboring uORFs initiated by AUG or near-cognate start codons, in non-starved or starved cells. Thus, very few mRNAs (possibly only one) appear to employ eIF2A for Met-tRNAi recruitment in yeast cells, even when eIF2 function is attenuated by stress.

Early is Better: Report of a Cowden Syndrome

In the clinical practice, it is not common for pediatricians to visit children with overgrowth phenotype. When it happens, it is important to focus on the age of manifestations and research the pathogenic causes using appropriate genetic test. Cowden syndrome is one of these rare causes; it is an autosomal dominant genodermatosis characterized by multiple hamartomas of ectodermal, mesodermal, and endodermal origin. It is caused by loss of function mutations in the phosphatase and tensin homolog (PTEN) gene located on chromosome 10q23.1 Loss of function of the PTEN gene contributes to overgrowth and risk for a variety of cancers including breast, thyroid, endometrium, skin, kidneys, and colon. The early diagnosis of Cowden disease allows a careful monitoring of the patients who are facing the risk of cancer transformation, which is the principal complication of the condition.

The intrinsically disordered region of eIF5B stimulates IRES usage and nucleates biological granule formation

Cells activate stress response pathways to survive adverse conditions. Such responses involve the inhibition of global cap-dependent translation. This inhibition is a block that essential transcripts must escape via alternative methods of translation initiation, e.g., an internal ribosome entry site (IRES). IRESs have distinct structures and generally require a limited repertoire of translation factors. Cellular IRESs have been identified in many critical cellular stress response transcripts. We previously identified cellular IRESs in the murine insulin receptor (Insr) and insulin-like growth factor 1 receptor (Igf1r) transcripts and demonstrated their resistance to eukaryotic initiation factor 4F (eIF4F) inhibition. Here, we find that eIF5B preferentially promotes Insr, Igf1r, and hepatitis C virus IRES activity through a non-canonical mechanism that requires its highly charged and disordered N terminus. We find that the N-terminal region of eIF5B can drive cytoplasmic granule formation. This eIF5B granule is triggered by cellular stress and is sufficient to specifically promote IRES activity.

Increased levels of eIF2A inhibit translation by sequestering 40S ribosomal subunits

eIF2A was the first eukaryotic initiator tRNA carrier discovered but its exact function has remained enigmatic. Uncharacteristic of translation initiation factors, eIF2A is reported to be non-cytosolic in multiple human cancer cell lines. Attempts to study eIF2A mechanistically have been limited by the inability to achieve high yield of soluble recombinant protein. Here, we developed a purification paradigm that yields ∼360-fold and ∼6000-fold more recombinant human eIF2A from Escherichia coli and insect cells, respectively, than previous reports. Using a mammalian in vitro translation system, we found that increased levels of recombinant human eIF2A inhibit translation of multiple reporter mRNAs, including those that are translated by cognate and near-cognate start codons, and does so prior to start codon recognition. eIF2A also inhibited translation directed by all four types of cap-independent viral IRESs, including the CrPV IGR IRES that does not require initiation factors or initiator tRNA, suggesting excess eIF2A sequesters 40S subunits. Supplementation with additional 40S subunits prevented eIF2A-mediated inhibition and pull-down assays demonstrated direct binding between recombinant eIF2A and purified 40S subunits. These data support a model that eIF2A must be kept away from the translation machinery to avoid sequestering 40S ribosomal subunits.

Blockade of Hepatocyte PCSK9 Ameliorates Hepatic Ischemia-Reperfusion Injury by Promoting Pink1-Parkin-Mediated Mitophagy

BACKGROUND & AIMS

Hepatic ischemia-reperfusion injury is a significant complication of partial hepatic resection and liver transplantation, impacting the prognosis of patients undergoing liver surgery. The protein proprotein convertase subtilisin/kexin type 9 (PCSK9) is primarily synthesized by hepatocytes and has been implicated in myocardial ischemic diseases. However, the role of PCSK9 in hepatic ischemia-reperfusion injury remains unclear. This study aims to investigate the role and mechanism of PCSK9 in hepatic ischemia-reperfusion injury.

METHODS

We first examined the expression of PCSK9 in mouse warm ischemia-reperfusion models and AML12 cells subjected to hypoxia/reoxygenation. Subsequently, we explored the impact of PCSK9 on liver ischemia-reperfusion injury by assessing mitochondrial damage and the resulting inflammatory response.

RESULTS

Our findings reveal that PCSK9 is up-regulated in response to ischemia-reperfusion injury and exacerbates hepatic ischemia-reperfusion injury. Blocking PCSK9 can alleviate hepatocyte mitochondrial damage and the consequent inflammatory response mediated by ischemia-reperfusion. Mechanistically, this protective effect is dependent on mitophagy.

CONCLUSIONS

Inhibiting PCSK9 in hepatocytes attenuates the inflammatory responses triggered by reactive oxygen species and mitochondrial DNA by promoting PINK1-Parkin-mediated mitophagy. This, in turn, ameliorates hepatic ischemia-reperfusion injury.

Novel anti-PTEN C2 domain monoclonal antibodies to analyse the expression and function of PTEN isoform variants

PTEN is a major tumor suppressor gene frequently mutated in human tumors, and germline PTEN gene mutations are the molecular diagnostic of PTEN Hamartoma Tumor Syndrome (PHTS), a heterogeneous disorder that manifests with multiple hamartomas, cancer predisposition, and neurodevelopmental alterations. A diversity of translational and splicing PTEN isoforms exist, as well as PTEN C-terminal truncated variants generated by disease-associated nonsense mutations. However, most of the available anti-PTEN monoclonal antibodies (mAb) recognize epitopes at the PTEN C-terminal tail, which may introduce a bias in the analysis of the expression of PTEN isoforms and variants. We here describe the generation and precise characterization of anti-PTEN mAb recognizing the PTEN C2-domain, and their use to monitor the expression and function of PTEN isoforms and PTEN missense and nonsense mutations associated to disease. These anti-PTEN C2 domain mAb are suitable to study the pathogenicity of PTEN C-terminal truncations that retain stability and function but have lost the PTEN C-terminal epitopes. The use of well-defined anti-PTEN mAb recognizing distinct PTEN regions, as the ones here described, will help to understand the deleterious effects of specific PTEN mutations in human disease.

Hyperphosphorylated PTEN exerts oncogenic properties

PTEN is a multifaceted tumor suppressor that is highly sensitive to alterations in expression or function. The PTEN C-tail domain, which is rich in phosphorylation sites, has been implicated in PTEN stability, localization, catalytic activity, and protein interactions, but its role in tumorigenesis remains unclear. To address this, we utilized several mouse strains with nonlethal C-tail mutations. Mice homozygous for a deletion that includes S370, S380, T382 and T383 contain low PTEN levels and hyperactive AKT but are not tumor prone. Analysis of mice containing nonphosphorylatable or phosphomimetic versions of S380, a residue hyperphosphorylated in human gastric cancers, reveal that PTEN stability and ability to inhibit PI3K-AKT depends on dynamic phosphorylation-dephosphorylation of this residue. While phosphomimetic S380 drives neoplastic growth in prostate by promoting nuclear accumulation of β-catenin, nonphosphorylatable S380 is not tumorigenic. These data suggest that C-tail hyperphosphorylation creates oncogenic PTEN and is a potential target for anti-cancer therapy.

Mitophagy as a mitochondrial quality control mechanism in myocardial ischemic stress: from bench to bedside

Myocardial ischemia reduces the supply of oxygen and nutrients to cardiomyocytes, leading to an energetic crisis or cell death. Mitochondrial dysfunction is a decisive contributor to the reception, transmission, and modification of cardiac ischemic signals. Cells with damaged mitochondria exhibit impaired mitochondrial metabolism and increased vulnerability to death stimuli due to disrupted mitochondrial respiration, reactive oxygen species overproduction, mitochondrial calcium overload, and mitochondrial genomic damage. Various intracellular and extracellular stress signaling pathways converge on mitochondria, so dysfunctional mitochondria tend to convert from energetic hubs to apoptotic centers. To interrupt the stress signal transduction resulting from lethal mitochondrial damage, cells can activate mitophagy (mitochondria-specific autophagy), which selectively eliminates dysfunctional mitochondria to preserve mitochondrial quality control. Different pharmacological and non-pharmacological strategies have been designed to augment the protective properties of mitophagy and have been validated in basic animal experiments and pre-clinical human trials. In this review, we describe the process of mitophagy in cardiomyocytes under ischemic stress, along with its regulatory mechanisms and downstream effects. Then, we discuss promising therapeutic approaches to preserve mitochondrial homeostasis and protect the myocardium against ischemic damage by inducing mitophagy.

Endothelial plasticity across PTEN and Hippo pathways: A complex hormetic rheostat modulated by extracellular vesicles

Vascularization is a multifactorial and spatiotemporally regulated process, essential for cell and tissue survival. Vascular alterations have repercussions on the development and progression of diseases such as cancer, cardiovascular diseases, and diabetes, which are the leading causes of death worldwide. Additionally, vascularization continues to be a challenge for tissue engineering and regenerative medicine. Hence, vascularization is the center of interest for physiology, pathophysiology, and therapeutic processes. Within vascularization, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and Hippo signaling have pivotal roles in the development and homeostasis of the vascular system. Their suppression is related to several pathologies, including developmental defects and cancer. Non-coding RNAs (ncRNAs) are among the regulators of PTEN and/or Hippo pathways during development and disease. The purpose of this paper is to review and discuss the mechanisms by which exosome-derived ncRNAs modulate endothelial cell plasticity during physiological and pathological angiogenesis, through the regulation of PTEN and Hippo pathways, aiming to establish new perspectives on cellular communication during tumoral and regenerative vascularization.

Nuclear PTEN's Functions in Suppressing Tumorigenesis: Implications for Rare Cancers

Phosphatase and tensin homolog (PTEN) encodes a tumor-suppressive phosphatase with both lipid and protein phosphatase activity. The tumor-suppressive functions of PTEN are lost through a variety of mechanisms across a wide spectrum of human malignancies, including several rare cancers that affect pediatric and adult populations. Originally discovered and characterized as a negative regulator of the cytoplasmic, pro-oncogenic phosphoinositide-3-kinase (PI3K) pathway, PTEN is also localized to the nucleus where it can exert tumor-suppressive functions in a PI3K pathway-independent manner. Cancers can usurp the tumor-suppressive functions of PTEN to promote oncogenesis by disrupting homeostatic subcellular PTEN localization. The objective of this review is to describe the changes seen in PTEN subcellular localization during tumorigenesis, how PTEN enters the nucleus, and the spectrum of impacts and consequences arising from disrupted PTEN nuclear localization on tumor promotion. This review will highlight the immediate need in understanding not only the cytoplasmic but also the nuclear functions of PTEN to gain more complete insights into how important PTEN is in preventing human cancers.

Intracellular complement: Evidence, definitions, controversies, and solutions

The term "intracellular complement" has been introduced recently as an umbrella term to distinguish functions of complement proteins that take place intracellularly, rather than in the extracellular environment. However, this rather undefined term leaves some confusion as to the classification of what intracellular complement really is, and as to which intracellular compartment(s) it should refer to. In this review, we will describe the evidence for both canonical and non-canonical functions of intracellular complement proteins, as well as the current controversies and unanswered questions as to the nature of the intracellular complement. We also suggest new terms to facilitate the accurate description and discussion of specific forms of intracellular complement and call for future experiments that will be required to provide more definitive evidence and a better understanding of the mechanisms of intracellular complement activity.

Role of Tumor Suppressor PTEN and Its Regulation in Malignant Transformation of Endometrium

Tumor-suppressive effects of PTEN are well-known, but modern evidence suggest that they are not limited to its ability to inhibit pro-oncogenic PI3K/AKT signaling pathway. Features of PTEN structure facilitate its interaction with substrates of different nature and display its activity in various ways both in the cytoplasm and in cell nuclei, which makes it possible to take a broader look at its ability to suppress tumor growth. The possible mechanisms of the loss of PTEN effects are also diverse - PTEN can be regulated at many levels, leading to change in the protein activity or its amount in the cell, while their significance for the development of malignant tumors has yet to be studied. Here we summarize the current data on the PTEN structure, its functions and changes in its regulatory mechanisms during malignant transformation of the cells, focusing on one of the most sensitive to the loss of PTEN types of malignant tumors - endometrial cancer.

PTEN Dual Lipid- and Protein-Phosphatase Function in Tumor Progression

Simple Summary

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a multifunctional tumor suppressor with protein- and lipid-phosphatase activities. The inactivation of PTEN is commonly found in all human cancers and is correlated with tumor progression. PTEN-lipid-phosphatase activity has been well documented to dephosphorylate phosphatidylinositol-3, 4, 5-phosphate (PIP3), which hinders cell growth and survival by dampening the PI3K and AKT signaling activity. PTEN-protein-phosphatase activity is less well studied and understood. Recent studies have reported that PTEN-protein-phosphatase activity dephosphorylates the different proteins and acts in various cell functions. We here review the PTEN mutations and protein-phosphatase substrates in tumor progression. We aim to address the gap in our understanding as to how PTEN protein phosphatase contributes to its tumor-suppression functions.

Abstract

PTEN is the second most highly mutated tumor suppressor in cancer, following only p53. The PTEN protein functions as a phosphatase with lipid- and protein-phosphatase activity. PTEN-lipid-phosphatase activity dephosphorylates PIP3 to form PIP2, and it then antagonizes PI3K and blocks the activation of AKT, while its protein-phosphatase activity dephosphorylates different protein substrates and plays various roles in tumorigenesis. Here, we review the PTEN mutations and protein-phosphatase substrates in tumorigenesis and metastasis. Our purpose is to clarify how PTEN protein phosphatase contributes to its tumor-suppressive functions through PI3K-independent activities.

PTEN: An Emerging Potential Target for Therapeutic Intervention in Respiratory Diseases

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a potent tumor suppressor that regulates several key cellular processes, including proliferation, survival, genomic integrity, migration, and invasion, via PI3K-dependent and independent mechanisms. A subtle decrease in PTEN levels or catalytic activity is implicated not only in cancer but also in a wide spectrum of other diseases, including various respiratory diseases. A systemic overview of the advances in the molecular and cellular mechanisms of PTEN involved in the initiation and progression of respiratory diseases may offer novel targets for the development of effective therapeutics for the treatment of respiratory diseases. In the present review, we highlight the novel findings emerging from current research on the role of PTEN expression and regulation in airway pathological conditions such as asthma/allergic airway inflammation, pulmonary hypertension (PAH), chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and other acute lung injuries (ALI). Moreover, we discuss the clinical implications of PTEN alteration and recently suggested therapeutic possibilities for restoration of PTEN expression and function in respiratory diseases.

The Role of PTEN-L in Modulating PINK1-Parkin-Mediated Mitophagy

An inherent challenge that mitochondria face is the continuous exposure to diverse stresses which increase their likelihood of dysregulation. In response, human cells have evolved sophisticated quality control mechanisms to identify and eliminate abnormal dysfunctional mitochondria. One pivotal mitochondrial quality control pathway is PINK1/Parkin-dependent mitophagy which mediates the selective removal of the dysfunctional mitochondria from the cell by autophagy. PTEN-induced putative kinase 1 (PINK1) is a mitochondrial Ser/Thr kinase that was originally identified as a gene responsible for autosomal recessive early-onset Parkinson's disease (PD). Notably, upon failure of mitochondrial import, Parkin, another autosomal-recessive PD gene, is recruited to mitochondria and mediates the autophagic clearance of deregulated mitochondria. Importantly, recruitment of Parkin to damaged mitochondria hinges on the accumulation of PINK1 on the outer mitochondrial membrane (OMM). Normally, PINK1 is imported from the cytosol through the translocase of the outer membrane (TOM) complex, a large multimeric channel responsible for the import of most mitochondrial proteins. After import, PINK1 is rapidly degraded. Thus, at steady-state, PINK1 levels are kept low. However, upon mitochondrial import failure, PINK1 accumulates and forms a high-molecular weight > 700 kDa complex with TOM on the OMM. Thus, PINK1 functions as sensor, tagging dysfunctional mitochondria for Parkin-mediated mitophagy. Although much has been learned about the function of PINK1 in mitophagy, the biochemical and structural basis of negative regulation of PINK1 operation and functions is far from clear. Recent work unveiled new players as PTEN-l as negative regulator of PINK1 function. Herein, we review key aspects of mitophagy and PINK1/Parkin-mediated mitophagy with highlighting the role of negative regulation of PINK1 function and presenting some of the key future directions in PD cell biology.

Furin extracellularly cleaves secreted PTENα/β to generate C-terminal fragment with a tumor-suppressive role

PTENα and PTENβ (PTENα/β), two long translational variants of phosphatase and tensin homolog on chromosome 10 (PTEN), exert distinct roles from canonical PTEN, including promoting carcinogenesis and accelerating immune-resistant cancer progression. However, their roles in carcinogenesis remain greatly unknown. Herein, we report that, after secreting into the extracellular space, PTENα/β proteins are efficiently cleaved into a short N-terminal and a long C-terminal fragment by the proprotein convertase Furin at a polyarginine stretch in their N-terminal extensions. Although secreted PTENα/β and their cleaved fragment cannot enter cells, treatment of the purified C-terminal fragment but not cleavage-resistant mutants of PTENα exerts a tumor-suppressive role in vivo. As a result, overexpression of cleavage-resistant PTENα mutants manifest a tumor-promoting role more profound than that of wild-type PTENα. In line with these, the C-terminal fragment is significantly downregulated in liver cancer tissues compared to paired normal tissues, which is consistent with the downregulated expression of Furin. Collectively, we show that extracellular PTENα/β present opposite effects on carcinogenesis from intracellular PTENα/β, and propose that the tumor-suppressive C-terminal fragment of PTENα/β might be used as exogenous agent to treat cancer.

Human UFSP1 translated from an upstream near-cognate initiation codon functions as an active UFM1-specific protease

Ubiquitin-fold modifier 1 (UFM1) is a recently identified ubiquitin-like posttranslational modification with important biological functions. However, the regulatory mechanisms governing UFM1 modification of target proteins (UFMylation) and the cellular processes controlled by UFMylation remain largely unknown. It has been previously shown that a UFM1-specific protease (UFSP2) mediates the maturation of the UFM1 precursor and drives the de-UFMylation reaction. Furthermore, it has long been thought that UFSP1, an ortholog of UFSP2, is inactive in many organisms, including human, because it lacks an apparent protease domain when translated from the canonical start codon (⁴⁴⁵AUG). Here, we demonstrate using the combination of site-directed mutagenesis, CRISPR/Cas9–mediated genome editing, and mass spectrometry approaches that translation of human UFSP1 initiates from an upstream near-cognate codon, ²¹⁷CUG, via eukaryotic translation initiation factor eIF2A-mediated translational initiation rather than from the annotated ⁴⁴⁵AUG, revealing the presence of a catalytic protease domain containing a Cys active site. Moreover, we show that both UFSP1 and UFSP2 mediate maturation of UFM1 and de-UFMylation of target proteins. This study demonstrates that human UFSP1 functions as an active UFM1-specific protease, thus contributing to our understanding of the UFMylation/de-UFMylation process.

Protein synthesis control in cancer: selectivity and therapeutic targeting

Translational control of mRNAs is a point of convergence for many oncogenic signals through which cancer cells tune protein expression in tumorigenesis. Cancer cells rely on translational control to appropriately adapt to limited resources while maintaining cell growth and survival, which creates a selective therapeutic window compared to non-transformed cells. In this review, we first discuss how cancer cells modulate the translational machinery to rapidly and selectively synthesize proteins in response to internal oncogenic demands and external factors in the tumor microenvironment. We highlight the clinical potential of compounds that target different translation factors as anti-cancer therapies. Next, we detail how RNA sequence and structural elements interface with the translational machinery and RNA-binding proteins to coordinate the translation of specific pro-survival and pro-growth programs. Finally, we provide an overview of the current and emerging technologies that can be used to illuminate the mechanisms of selective translational control in cancer cells as well as within the microenvironment.

Mechanistic convergence across initiation sites for RAN translation in fragile X associated tremor ataxia syndrome

Repeat associated non-AUG (RAN) translation of CGG repeats in the 5'UTR of FMR1 produces toxic proteins that contribute to fragile X-associated tremor/ataxia syndrome (FXTAS) pathogenesis. The most abundant RAN product, FMRpolyG, initiates predominantly at an ACG upstream of the repeat. Accurate FMRpolyG measurements in FXTAS patients are lacking. We used data-dependent acquisition and parallel reaction monitoring (PRM) mass spectrometry coupled with stable isotope labeled standard peptides to identify signature FMRpolyG fragments in patient samples. Following immunoprecipitation, PRM detected FMRpolyG signature peptides in transfected cells, and FXTAS tissues and cells, but not in controls. We identified two amino-terminal peptides: an ACG-initiated Ac-MEAPLPGGVR and a GUG-initiated Ac-TEAPLPGGVR, as well as evidence for RAN translation initiation within the CGG repeat itself in two reading frames. Initiation at all sites increased following cellular stress, decreased following eIF1 overexpression and was eIF4A and M7G cap-dependent. These data demonstrate that FMRpolyG is quantifiable in human samples and FMR1 RAN translation initiates via similar mechanisms for near-cognate codons and within the repeat through processes dependent on available initiation factors and cellular environment.

circPTEN1, a circular RNA generated from PTEN, suppresses cancer progression through inhibition of TGF-β/Smad signaling

Background

PTEN is one of the most frequently mutated genes in human cancer. Although the roles of canonical PTEN protein and PTEN isoforms have been extensively explored, the current understanding of PTEN family members cannot fully illustrate the diversity of their roles in biological processes and tumor development. Notably, the function of noncoding RNAs arising from PTEN has been less elucidated.

Methods

We searched circBase and circInteractome to analyze the potential of PTEN for generating circRNAs. Then, Sanger sequencing, RNase R and Actinomycin D assays were used to verify the ring structure of circPTEN1. In situ hybridization and qRT-PCR were used to determine the level of circPTEN1 in peritumor and tumor tissues of colorectal cancer (CRC). Furthermore, functional experiments, including Transwell assay, 3D multicellular tumor spheroid invasion assay and metastasis models, were performed using circPTEN1 knockdown and overexpression cell lines in vitro and in vivo to investigate the effects of circPTEN1 on tumor metastasis in CRC. Mechanistically, luciferase reporter assay, fluorescence in situ hybridization, electrophoretic mobility shift assay, RNA immunoprecipitation, RNA pull-down and mass spectrometry were executed.

Results

We identified a circular RNA generated from the PTEN gene, designated circPTEN1, that is frequently downregulated in colorectal cancer, and decreased expression of circPTEN1 predicts poor survival. Low expression of circPTEN1 promotes metastasis in PDX models in vivo and accelerates cancer cell invasion in vitro, whereas overexpression of circPTEN1 reveals opposite roles. Mechanically, we found that circPTEN1 is capable of binding the MH2 domain of Smad4 to disrupt its physical interaction with Smad2/3, which reduces the formation and subsequent nucleus translocation of Smad complexes and consequently suppresses the expression of its downstream genes associated with epithelial-mesenchymal transition upon TGF-β stimulation. Furthermore, we found that eIF4A3 suppresses the cyclization of circPTEN1 by directly binding to the circPTEN1 flanking region.

Conclusions

Our study uncovered a novel PTEN gene-generated circRNA with a tumor suppression function, and further revealed the mechanism of circPTEN1 in CRC metastasis mediated by TGF-β. The identification of circPTEN1 provides a new direction for PTEN investigation, and elucidation of circPTEN1/TGF-β/Smad signaling may pave the way for the development of a potential therapeutic strategy for the suppression of cancer progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01495-y.

PTEN and AKT/GSK-3β/CRMP-2 signaling pathway are involved in neuronal apoptosis and axonal injury in early brain injury after SAH in rats

In early brain injury (EBI) after subarachnoid hemorrhage (SAH), white matter (WM) axonal injury plays a key role in the prognosis of the disease. The purpose of this study was to investigate the effects of phosphatase and tensin homolog deleted on chromosome ten (PTEN) on axonal injury and neuronal apoptosis post-SAH in rats and to find its underlying mechanism. Adeno-associated virus was injected into the lateral ventricle to suppress or promote PTEN. Neural function post-SAH in animals was determined by the modified Garcia score, beam balance, and Rotarod test, and the blood–brain barrier disruption was assessed by the brain water content. Axonal injury post-SAH was observed by TEM and determined by IF, and neuron apoptosis was measured by TUNEL staining. The mechanism was analyzed by Western blot to detect p-PTEN/PTEN, p-AKT/AKT, p-GSK-3β/GSK-3β, p-CRMP-2/CRMP-2, axonal injury marker β-APP and pro- and anti-apoptosis proteins, including Bax and Bcl-2, expression. We found 1. After knocking down PTEN, neuronal apoptosis and axonal injury were alleviated, and nerve function and blood–brain barrier were protected; accordingly, after overexpression of PTEN, neuronal apoptosis and axon damage were aggravated, and nerve function damage and blood–brain barrier damage were increased. 2. PTEN and AKT/GSK-3β/CRMP-2 pathway were jointly involved in regulating neuronal apoptosis and WM axon injury after SAH. According to our research, PTEN was a negative factor of EBI, and together with the AKT/GSK-3β/CRMP-2 signaling pathway aggravates neuronal apoptosis and WM axon damage after SAH. Inhibition of PTEN expression may become a new target for SAH treatment.

Molecular Signaling to Preserve Mitochondrial Integrity against Ischemic Stress in the Heart: Rescue or Remove Mitochondria in Danger

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide, and ischemic heart disease is the most common cause of heart failure (HF). The heart is a high-energy demanding organ, and myocardial energy reserves are limited. Mitochondria are the powerhouses of the cell, but under stress conditions, they become damaged, release necrotic and apoptotic factors, and contribute to cell death. Loss of cardiomyocytes plays a significant role in ischemic heart disease. In response to stress, protective signaling pathways are activated to limit mitochondrial deterioration and protect the heart. To prevent mitochondrial death pathways, damaged mitochondria are removed by mitochondrial autophagy (mitophagy). Mitochondrial quality control mediated by mitophagy is functionally linked to mitochondrial dynamics. This review provides a current understanding of the signaling mechanisms by which the integrity of mitochondria is preserved in the heart against ischemic stress.

PTENα is responsible for protection of brain against oxidative stress during aging

Neural cells are continuously subjected to oxidative stress arising from electrochemical activity, and cellular protection systems can turn on the oxidative stress response to detect and alleviate adverse conditions. However, the function and mechanism of the protective systems are complicated and remain largely elusive. We report that PTENα, an isoform of the PTEN family, mediates defense signaling in response to oxidative stress during brain aging. We show that genetic ablation of Ptenα in mice increases oxidative stress and results in neuronal cell death, culminating in accelerated decline of cognition and motor coordination as age increases. PTENα maintains COX activity and promotes energy metabolism through abrogating NEDD4L-mediated degradation of COX4 in response to oxidative stress. In the presence of Parkinson's disease-associated mutation, PTENα loses the capability to protect COX4 and ameliorate defects caused by Ptenα deletion. Our study reveals an important role of PTENα in response to oxidative stress. We propose that dysregulation of PTENα signaling may accelerate the rate of brain aging and promote the development of neurodegenerative disorders.

Phosphatidylinositol 4,5-bisphosphate is regenerated by speeding of the PI 4-kinase pathway during long PLC activation

The dynamic metabolism of membrane phosphoinositide lipids involves several cellular compartments including the ER, Golgi, and plasma membrane. There are cycles of phosphorylation and dephosphorylation and of synthesis, transfer, and breakdown. The simplified phosphoinositide cycle comprises synthesis of phosphatidylinositol in the ER, transport, and phosphorylation in the Golgi and plasma membranes to generate phosphatidylinositol 4,5-bisphosphate, followed by receptor-stimulated hydrolysis in the plasma membrane and return of the components to the ER for reassembly. Using probes for specific lipid species, we have followed and analyzed the kinetics of several of these events during stimulation of M₁ muscarinic receptors coupled to the G-protein G_q. We show that during long continued agonist action, polyphosphorylated inositol lipids are initially depleted but then regenerate while agonist is still present. Experiments and kinetic modeling reveal that the regeneration results from gradual but massive up-regulation of PI 4-kinase pathways rather than from desensitization of receptors. Golgi pools of phosphatidylinositol 4-phosphate and the lipid kinase PI4KIIIα (PI4KA) contribute to this homeostatic regeneration. This powerful acceleration, which may be at the level of enzyme activity or of precursor and product delivery, reveals strong regulatory controls in the phosphoinositide cycle.

PTEN hamartoma tumour syndrome: what happens when there is no PTEN germline mutation?

Hereditary cancer syndromes represent ~10% of all incident cancers. It is important to identify individuals having these disorders because, unlike patients with sporadic cancer, these patients require specialised life-long care, with implications for their families. Importantly, the identification of alterations in cancer-predisposing genes facilitates gene-informed molecular diagnosis, cancer risk assessment and gene-specific clinical management. Moreover, knowledge about gene function in the inherited cancers offers insights towards biological processes pertinent to the more common sporadic cancers. Conversely, without a known gene, clinical management is less precise, and it is impossible to offer predictive testing of family members. PTEN hamartoma tumour syndrome (PHTS) is an umbrella term encompassing four overgrowth and cancer predisposition disorders associated with germline PTEN mutations. With time, it became evident that only a finite subset of individuals with PHTS-associated phenotypes harbour germline PTEN mutations. Therefore, non-PTEN aetiologies exist in PTEN wildtype patients. Indeed, gene discovery efforts over the last decade elucidated multiple candidate cancer predisposition genes. While a subset of genes (e.g. AKT1, PIK3CA) are biologically plausible as being key effectors within the PTEN signalling cascade, other genes required meticulous functional interrogation to explain their contribution to PHTS-related phenotypes. Collectively, the extensive phenotypic heterogeneity of the clinical syndromes typically united by PTEN is reflected by the genetic heterogeneity revealed through gene discovery. Validating these gene discoveries is critical because, while PTEN wildtype patients can be diagnosed clinically, they do not have the benefit of specific gene-informed risk assessment and subsequent management.

PTENα functions as an immune suppressor and promotes immune resistance in PTEN-mutant cancer

PTEN is frequently mutated in human cancers and PTEN mutants promote tumor progression and metastasis. PTEN mutations have been implicated in immune regulation, however, the underlying mechanism is largely unknown. Here, we report that PTENα, the isoform of PTEN, remains active in cancer bearing stop-gained PTEN mutations. Through counteraction of CD8⁺ T cell-mediated cytotoxicity, PTENα leads to T cell dysfunction and accelerates immune-resistant cancer progression. Clinical analysis further uncovers that PTENα-active mutations suppress host immune responses and result in poor prognosis in cancer as relative to PTENα-inactive mutations. Furthermore, germline deletion of Ptenα in mice increases cell susceptibility to immune attack through augmenting stress granule formation and limiting synthesis of peroxidases, leading to massive oxidative cell death and severe inflammatory damage. We propose that PTENα protects tumor from T cell killing and thus PTENα is a potential target in antitumor immunotherapy.

PTENα is an N-terminally extended isoform of PTEN, a gene frequently mutated in human cancers. Here the authors show that PTENα remains active in PTEN-mutant cancers and is associated with tumor immune escape by promoting tumor cell resistance to T cell cytotoxicity.

Preparation and characterization of a polyclonal antibody against PTEN-Long

Phosphatase and tensin homolog-long (PTEN-L) is a translational isoform of PTEN, which exists in both intracellular and extracellular locations. Previous studies demonstrated that PTEN-L could inhibit oncogenesis due to its lipid phosphatase activity. However, recent studies found that PTEN-L could promote the proliferation of some types of cancer cells. Moreover, as a protein phosphatase, PTEN-L can suppress mitophagy by counteracting PTEN-induced putative kinase protein 1 (PINK1)-Parkin-mediated ubiquitin phosphorylation, namely, PTEN-L is critical for exploring the mitophagy progression and the treatment of mitochondrial diseases. Accounting for the critical functions of PTEN-L, its antibody can be used for the treatment or prognosis of tumors and mitochondrial diseases. Currently, the commercial antibody of PTEN-L is not available. In our study, the recombinant PTEN-L protein was expressed in Escherichia coli BL21 and used as an antigen to immunize Japan's big-eared white rabbit for the preparation of polyclonal antibody. The PTEN-L protein can be captured by PTEN-L antibody specifically and effectively. Taken together, a PTEN_L antibody is a valuable tool for further exploring the function of PTEN-L in oncogenesis and mitochondrial diseases, and it would be a new choice for the prognosis or treatment of cancer and mitochondrial diseases.

Pseudomonas aeruginosa Consumption of Airway Metabolites Promotes Lung Infection

Prevailing dogma indicates that the lung of cystic fibrosis (CF) individuals is infected by multiple pathogens due to the abundant accumulation of mucus, which traps most of inhaled organisms. However, this hypothesis does not explain how specific opportunists, like Pseudomonas aeruginosa, are selected in the CF lung to cause chronic disease. This strongly suggests that other factors than mucus are accrued in the human airway and might predispose to bacterial disease, especially by P. aeruginosa. In this review we discuss the role of macrophage metabolites, like succinate and itaconate, in P. aeruginosa pneumonia. We analyze how dysfunction of the CF transmembrane conductance regulator (CFTR) favors release of these metabolites into the infected airway, and how P. aeruginosa exploits these elements to induce transcriptomic and metabolic changes that increase its capacity to cause intractable disease. We describe the host and pathogen pathways associated with succinate and itaconate catabolism, mechanisms of bacterial adaptation to these determinants, and suggest how both experimental settings and future therapies should consider macrophage metabolites abundance to better study P. aeruginosa pathogenesis.

Protein tyrosine phosphatome metabolic screen identifies TC-PTP as a positive regulator of cancer cell bioenergetics and mitochondrial dynamics

Metabolic reprogramming occurs in cancer cells and is regulated partly by the opposing actions of tyrosine kinases and tyrosine phosphatases. Several members of the protein tyrosine phosphatase (PTP) superfamily have been linked to cancer as either pro-oncogenic or tumor-suppressive enzymes. In order to investigate which PTPs can modulate the metabolic state of cancer cells, we performed an shRNA screen of PTPs in HCT116 human colorectal cancer cells. Among the 72 PTPs efficiently targeted, 24 were found to regulate mitochondrial respiration, 8 as negative and 16 as positive regulators. Of the latter, we selected TC-PTP (PTPN2) for further characterization since inhibition of this PTP resulted in major functional defects in oxidative metabolism without affecting glycolytic flux. Transmission electron microscopy revealed an increase in the number of damaged mitochondria in TC-PTP-null cells, demonstrating the potential role of this PTP in regulating mitochondrial homeostasis. Downregulation of STAT3 by siRNA-mediated silencing partially rescued the mitochondrial respiration defect observed in TC-PTP-deficient cells, supporting the role of this signaling axis in regulating mitochondrial activity. In addition, mitochondrial stress prevented an increased expression of electron transport chain-related genes in cells with TC-PTP silencing, correlating with decreased ATP production, cellular proliferation, and migration. Our shRNA-based metabolic screen revealed that PTPs can serve as either positive or negative regulators of cancer cell metabolism. Taken together, our findings uncover a new role for TC-PTP as an activator of mitochondrial metabolism, validating this PTP as a key target for cancer therapeutics.

Alternative Splicing of MoPTEN Is Important for Growth and Pathogenesis in Magnaporthe oryzae

Human PTEN, a dual-phosphatase tumor suppressor, is frequently dysregulated by alternative splicing. Fungi harbor PTEN homologs, but alternative splicing of fungal PTENs has not been reported as far as we know. Here, we described an alternative splicing case in the PTEN homolog of Magnaporthe oryzae (MoPTEN). Two splice variants of MoPTEN were detected and identified, which are resulted from an intron retention and exclusion (MoPTEN-1/2). Both proteins were different in lipid and protein phosphatase activity and in expression patterns. The MoPTEN deletion mutant (ΔMoPTEN) showed the defects in conidiation, appressorium formation, and pathogenesis. ΔMoPTEN could be completely restored by MoPTEN, but rescued partially by MoPTEN-1 in the defect of conidium and appressorium formation, and by MoPTEN-2 in the defect of invasive development. Assays to assess sensitivity to oxidative stress reveal the involvement of MoPTEN-2 in scavenging exogenous and host-derived H₂O₂. Taken together, MoPTEN undergoes alternative splicing, and both variants cooperatively contribute to conidium and appressorium development, and invasive hyphae growth in plant cells, revealing a novel disease development pathway in M. oryzae.

Redefining the PTEN promoter: Identification of novel upstream transcription start regions

Germline mutation of PTEN is causally observed in Cowden syndrome (CS) and is one of the most common, penetrant risk genes for autism spectrum disorder (ASD). However, the majority of individuals who present with CS-like clinical features are PTEN-mutation negative. Reassessment of PTEN promoter regulation may help explain abnormal PTEN dosage, as only the minimal promoter and coding regions are currently included in diagnostic PTEN mutation analysis. Therefore, we reanalyzed the architecture of the PTEN promoter using next-generation sequencing datasets. Specifically, run-on sequencing assays identified two additional transcription start regions (TSRs) at -2053 and - 1906 basepairs from the canonical start of PTEN, thus extending the PTEN 5'UTR and redefining the PTEN promoter. We show that these novel upstream TSRs are active in cancer cell lines, human cancer, and normal tissue. Further, these TSRs can produce novel PTEN transcripts due to the introduction of new splice donors at -2041, -1826, and - 1355, which may allow for splicing out of the PTEN 5'UTR or the first and second exon in upstream-initiated transcripts. Combining ENCODE ChIP-seq and pertinent literature, we also compile and analyze all transcription factors (TFs) binding at the redefined PTEN locus. Enrichment analyses suggest that TFs bind specifically to the upstream TSRs may be implicated in inflammatory processes. Together, these data redefine the architecture of the PTEN promoter, an important step toward a comprehensive model of PTEN transcription regulation, a basis for future investigations into the new promoters' role in disease pathogenesis.

Multifaceted control of mRNA translation machinery in cancer

The mRNA translation machinery is tightly regulated through several, at times overlapping, mechanisms that modulate its efficiency and accuracy. Due to their fast rate of growth and metabolism, cancer cells require an excessive amount of mRNA translation and protein synthesis. However, unfavorable conditions, such as hypoxia, amino acid starvation, and oxidative stress, which are abundant in cancer, as well as many anti-cancer treatments inhibit mRNA translation. Cancer cells adapt to the various internal and environmental stresses by employing specialised transcript-specific translation to survive and gain a proliferative advantage. We will highlight the major signaling pathways and mechanisms of translation that regulate the global or mRNA-specific translation in response to the intra- or extra-cellular signals and stresses that are key components in the process of tumourigenesis.

PTENε suppresses tumor metastasis through regulation of filopodia formation

PTEN is one of the most frequently mutated genes in malignancies and acts as a powerful tumor suppressor. Tumorigenesis is involved in multiple and complex processes including initiation, invasion, and metastasis. The complexity of PTEN function is partially attributed to PTEN family members such as PTENα and PTENβ. Here, we report the identification of PTENε (also named as PTEN5), a novel N‐terminal‐extended PTEN isoform that suppresses tumor invasion and metastasis. We show that the translation of PTENε/PTEN5 is initiated from the CUG⁸¹⁶ codon within the 5′UTR region of PTEN mRNA. PTENε/PTEN5 mainly localizes in the cell membrane and physically associates with and dephosphorylates VASP and ACTR2, which govern filopodia formation and cell motility. We found that endogenous depletion of PTENε/PTEN5 promotes filopodia formation and enhances the metastasis capacity of tumor cells. Overall, we identify a new isoform of PTEN with distinct subcellular localization and molecular function compared to the known members of the PTEN family. These findings advance our current understanding of the importance and diversity of PTEN functions.

Recent advances in PTEN signalling axes in cancer

In over two decades since the discovery of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), nearly 18,000 publications have attempted to elucidate its functions and roles in normal physiology and disease. The frequent disruption of PTEN in cancer cells was a strong indication that it had critical roles in tumour suppression. Germline PTEN mutations have been identified in patients with heterogeneous tumour syndromic diseases, known as PTEN hamartoma tumour syndrome (PHTS), and in some individuals with autism spectrum disorders (ASD). Today we know that by limiting oncogenic signalling through the phosphoinositide 3-kinase (PI3K) pathway, PTEN governs a number of processes including survival, proliferation, energy metabolism, and cellular architecture. Some of the most exciting recent advances in the understanding of PTEN biology and signalling have revisited its unappreciated roles as a protein phosphatase, identified non-enzymatic scaffold functions, and unravelled its nuclear function. These discoveries are certain to provide a new perspective on its full tumour suppressor potential, and knowledge from this work will lead to new anti-cancer strategies that exploit PTEN biology. In this review, we will highlight some outstanding questions and some of the very latest advances in the understanding of the tumour suppressor PTEN.

Redox Regulation of PTEN by Peroxiredoxins

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is known as a tumor suppressor gene that is frequently mutated in numerous human cancers and inherited syndromes. PTEN functions as a negative regulator of PI3K/Akt signaling pathway by dephosphorylating phosphatidylinositol (3, 4, 5)-trisphosphate (PIP3) to phosphatidylinositol (4, 5)-bisphosphate (PIP2), which leads to the inhibition of cell growth, proliferation, cell survival, and protein synthesis. PTEN contains a cysteine residue in the active site that can be oxidized by peroxides, forming an intramolecular disulfide bond between Cys¹²⁴ and Cys⁷¹. Redox regulation of PTEN by reactive oxygen species (ROS) plays a crucial role in cellular signaling. Peroxiredoxins (Prxs) are a superfamily of peroxidase that catalyzes reduction of peroxides and maintains redox homeostasis. Mammalian Prxs have 6 isoforms (I-VI) and can scavenge cellular peroxides. It has been demonstrated that Prx I can preserve and promote the tumor-suppressive function of PTEN by preventing oxidation of PTEN under benign oxidative stress via direct interaction. Also, Prx II-deficient cells increased PTEN oxidation and insulin sensitivity. Furthermore, Prx III has been shown to protect PTEN from oxidation induced by 15s-HpETE and 12s-HpETE, these are potent inflammatory and pro-oxidant mediators. Understanding the tight connection between PTEN and Prxs is important for providing novel therapies. Herein, we summarized recent studies focusing on the relationship of Prxs and the redox regulation of PTEN.

A comprehensive review on the role of protein tyrosine phosphatases in gastric cancer development and progression

The main post-translational reversible modulation of proteins is phosphorylation and dephosphorylation, catalyzed by protein kinases (PKs) and protein phosphatases (PPs) which is crucial for homeostasis. Imbalance in this crosstalk can be related to diseases, including cancer. Plenty of evidence indicates that protein tyrosine phosphatases (PTPs) can act as tumor suppressors and tumor promoters. In gastric cancer (GC), there is a lack of understanding of the molecular aspects behind the tumoral onset and progression. Here we describe several members of the PTP family related to gastric carcinogenesis. We discuss the associated molecular mechanisms which support the down or up modulation of different PTPs. We emphasize the Helicobacter pylori (H. pylori) virulence which is in part associated with the activation of PTP receptors. We also explore the involvement of intracellular redox state in response to H. pylori infection. In addition, some PTP members are under influence by genetic mutations, epigenetics mechanisms, and miRNA modulation. The understanding of multiple aspects of PTPs in GC may provide new targets and perspectives on drug development.

Genetic Determinants of the Effects of Training on Muscle and Adipose Tissue Homeostasis in Obesity Associated with Lymphedema

It is widely accepted that metabolic changes associated with training are influenced by a person's genetic background. In this review, we explore the polymorphisms underlying interindividual variability in response to training of weight loss and muscle mass increase in obese individuals, with or without lymphedema, and in normal-weight subjects. We searched PubMed for articles in English published up to May 2019 using the following keywords: (((physical training[Title/Abstract] OR sport activity[Title/Abstract]) AND predisposition[Title/Abstract]) AND polymorphism [Title/Abstract]). We identified 38 single-nucleotide polymorphisms that may modulate the genetic adaptive response to training. The identification of genetic marker(s) that improve the beneficial effects of training may in perspective make it possible to assess training programs, which in combination with dietary intervention can optimize body weight reduction in obese subjects, with or without lymphedema. This is particularly important for patients with lymphedema because obesity can worsen the clinical status, and therefore, a personalized approach that could reduce obesity would be fundamental in the clinical management of lymphedema.

Airway immunometabolites fuel Pseudomonas aeruginosa infection

Pulmonary infections are associated with a brisk inflammatory reaction to bacterial surface components. Lipopolysaccharides (LPS) trigger macrophage activation and release of mitochondrial metabolites that control the intensity of the immune response. Whereas succinate induces oxidative stress (ROS), HIF1α stabilization, glycolysis and IL-1β release, itaconate suppresses inflammation by inhibiting succinate oxidation, glycolytic flux and promoting anti-oxidant Nrf2-HO-1 functions. P. aeruginosa is a major pathogen associated with acute and chronic lung infection. Although both secreted toxins, LPS and proteases are key factors to establish acute P. aeruginosa pneumonia, lack of these components in chronic P. aeruginosa isolates suggest these organisms exploit other mechanisms to adapt and persist in the lung. Upon inhalation, P. aeruginosa strains trigger airway macrophage reprograming and bacterial variants obtained from acutely and chronically infected subjects exhibit metabolic adaptation consistent with succinate and itaconate assimilation; namely, high expression of extracellular polysaccharides (EPS), reduced lptD-LPS function, increased glyoxylate shunt (GS) activity and substantial biofilm production. In this review we discuss recent findings illustrating how P. aeruginosa induces and adapts to macrophage metabolites in the human lung, and that catabolism of succinate and itaconate contribute to their formidable abilities to tolerate oxidative stress, phagocytosis and immune clearance.

Neddylation of PTEN regulates its nuclear import and promotes tumor development

PTEN tumor suppressor opposes the PI3K/Akt signaling pathway in the cytoplasm and maintains chromosomal integrity in the nucleus. Nucleus-cytoplasm shuttling of PTEN is regulated by ubiquitylation, SUMOylation and phosphorylation, and nuclear PTEN has been proposed to exhibit tumor-suppressive functions. Here we show that PTEN is conjugated by Nedd8 under high glucose conditions, which induces PTEN nuclear import without effects on PTEN stability. PTEN neddylation is promoted by the XIAP ligase and removed by the NEDP1 deneddylase. We identify Lys197 and Lys402 as major neddylation sites on PTEN. Neddylated PTEN accumulates predominantly in the nucleus and promotes rather than suppresses cell proliferation and metabolism. The nuclear neddylated PTEN dephosphorylates the fatty acid synthase (FASN) protein, inhibits the TRIM21-mediated ubiquitylation and degradation of FASN, and then promotes de novo fatty acid synthesis. In human breast cancer tissues, neddylated PTEN correlates with tumor progression and poor prognosis. Therefore, we demonstrate a previously unidentified pool of nuclear PTEN in the Nedd8-conjugated form and an unexpected tumor-promoting role of neddylated PTEN.

Approaches to Investigating the Protein Interactome of PTEN

The tumor suppressor phosphatase and tensin homologue (PTEN) is a redox-sensitive dual specificity phosphatase with an essential role in the negative regulation of the PI3K-AKT signaling pathway, affecting metabolic and cell survival processes. PTEN is commonly mutated in cancer, and dysregulation in the metabolism of PIP₃ is implicated in other diseases such as diabetes. PTEN interactors are responsible for some functional roles of PTEN beyond the negative regulation of the PI3K pathway and are thus of great importance in cell biology. Both high-data content proteomics-based approaches and low-data content PPI approaches have been used to investigate the interactome of PTEN and elucidate further functions of PTEN. While low-data content approaches rely on co-immunoprecipitation and Western blotting, and as such require previously generated hypotheses, high-data content approaches such as affinity pull-down proteomic assays or the yeast 2-hybrid system are hypothesis generating. This review provides an overview of the PTEN interactome, including redox effects, and critically appraises the methods and results of high-data content investigations into the global interactome of PTEN. The biological significance of findings from recent studies is discussed and illustrates the breadth of cellular functions of PTEN that can be discovered by these approaches.