A unified nomenclature and amino acid numbering for human PTEN

Therapeutic Potential of Translational Readthrough at Disease-Associated Premature Termination Codons From Tumor Suppressor Genes

Tumor suppressor genes are frequently targeted by mutations introducing premature termination codons (PTC) in the protein coding sequence, both in sporadic cancers and in the germline of patients with cancer predisposition syndromes. These mutations have a high pathogenic impact since they generate C-terminal truncated proteins with altered stability and function. In addition, PTC mutations trigger transcript degradation by nonsense-mediated mRNA decay. Suppression of PTC by translational readthrough restores protein biosynthesis and stabilizes the PTC-targeted mRNA, making a suitable therapeutic approach the reconstitution of active full-length tumor suppressor proteins by pharmacologically-induced translational readthrough. Here, we review the recent advances in small molecule pharmacological induction of translational readthrough of disease-associated PTC from tumor suppressor genes, and discuss the therapeutic potential of translational readthrough in specific groups of patients with hereditary syndromic cancers.

Potentiation by Protein Synthesis Inducers of Translational Readthrough of Pathogenic Premature Termination Codons in PTEN Isoforms

The PTEN tumor suppressor is frequently targeted in tumors and patients with PTEN hamartoma tumor syndrome (PHTS) through nonsense mutations generating premature termination codons (PTC) that may cause the translation of truncated non-functional PTEN proteins. We have previously described a global analysis of the readthrough reconstitution of the protein translation and function of the human canonical PTEN isoform by aminoglycosides. Here, we report the efficient functional readthrough reconstitution of the PTEN translational isoform PTEN-L, which displays a minimal number of PTC in its specific N-terminal extension in association with disease. We illustrate the importance of the specific PTC and its nucleotide proximal sequence for optimal readthrough and show that the more frequent human PTEN PTC variants and their mouse PTEN PTC equivalents display similar patterns of readthrough efficiency. The heterogeneous readthrough response of the different PTEN PTC variants was independent of the length of the PTEN protein being reconstituted, and we found a correlation between the amount of PTEN protein being synthesized and the PTEN readthrough efficiency. Furthermore, combination of aminoglycosides and protein synthesis inducers increased the readthrough response of specific PTEN PTC. Our results provide insights with which to improve the functional reconstitution of human-disease-related PTC pathogenic variants from PTEN isoforms by increasing protein synthesis coupled to translational readthrough.

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.

The Multifaceted Role of Baicalein in Cancer Management through Modulation of Cell Signalling Pathways

The roles of medicinal plants or their purified bioactive compounds have attracted attention in the field of health sciences due to their low toxicity and minimal side effects. Baicalein is an active polyphenolic compound, isolated from Scutellaria baicalensis, and plays a significant role in the management of different diseases. Epidemiologic studies have proven that there is an inverse association between baicalein consumption and disease severity. Baicalein is known to display anticancer activity through the inhibition of inflammation and cell proliferation. Additionally, the anticancer potential of baicalein is chiefly mediated through the modulation of various cell-signaling pathways, such as the induction of apoptosis, autophagy, cell cycle arrest, inhibition of angiogenesis, signal transducer and activator of transcription 3, and PI3K/Akt pathways, as well as the regulation of other molecular targets. Therefore, the current review aimed to explore the role of baicalein in different types of cancer along with mechanisms of action. Besides this, the synergistic effects with other anti-cancerous drugs and the nano-formulation based delivery of baicalein have also been discussed.

Glioma: molecular signature and crossroads with tumor microenvironment

In patients with glioblastoma, the average survival time with current treatments is short, mainly due to recurrences and resistance to therapy. This insufficient treatment success is, in large parts, due to the tremendous molecular heterogeneity of gliomas, which affects the overall prognosis and response to therapies and plays a vital role in gliomas’ grading. In addition, the tumor microenvironment is a major player for glioma development and resistance to therapy. Active communication between glioma cells and local or neighboring healthy cells and the immune environment promotes the cancerogenic processes and contributes to establishing glioma stem cells, which drives therapy resistance. Besides genetic alterations in the primary tumor, tumor-released factors, cytokines, proteins, extracellular vesicles, and environmental influences like hypoxia provide tumor cells the ability to evade host tumor surveillance machinery and promote disease progression. Moreover, there is increasing evidence that these players affect the molecular biological properties of gliomas and enable inter-cell communication that supports pro-cancerogenic cell properties. Identifying and characterizing these complex mechanisms are inevitably necessary to adapt therapeutic strategies and to develop novel measures. Here we provide an update about these junctions where constant traffic of biomolecules adds complexity in the management of glioblastoma.

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.

LncRNA as a multifunctional regulator in cancer multi-drug resistance

BACKGROUND

Malignant tumors have become the most dangerous disease in recent years. Chemotherapy is the most effective treatment for this disease; however, the problem of drug resistance has become even more common, which leads to the poor prognosis of patients suffering from cancers. Thus, necessary measures should be taken to address these problems at the earliest. Many studies have demonstrated that drug resistance is closely related to the abnormal expressions of long non-coding RNAs (lncRNAs).

METHODS AND RESULTS

This review aimed to summarize the molecular mechanisms underlying the association of lncRNAs and the development of drug resistance and to find potential strategies for the clinical diagnosis and treatment of cancer drug resistance. Studies showed that lncRNAs can regulate the expression of genes through chromatin remodeling, transcriptional regulation, and post-transcriptional processing. Furthermore, lncRNAs have been reported to be closely related to the occurrence of malignant tumors. In summary, lncRNAs have gained attention in related fields during recent years. According to previous studies, lncRNAs have a vital role in several different types of cancers owing to their multiple mechanisms of action. Different mechanisms have different functions that could result in different consequences in the same disease.

CONCLUSIONS

LncRNAs closely participated in cancer drug resistance by regulating miRNA, signaling pathways, proteins, cancer stem cells, pro- and ant-apoptosis, and autophagy. lncRNAs can be used as biomarkers of the possible treatment target in chemotherapy, which could provide solutions to the problem of drug resistance in chemotherapy in the future.

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.

Dysregulation of LINC00470 and METTL3 promotes chemoresistance and suppresses autophagy of chronic myelocytic leukaemia cells

Cytoplasmic lncRNAs have been found to directly interact with target mRNAs and regulate their stability. In this study, we aimed to study the molecular mechanism underlying the function of m⁶ A as a central regulator in chemoresistance and CML proliferation. In this study, we established three mice groups (control group, ADR-R group and ADR-R + shLINC00470 group). We detected PTEN mRNA expression in the presence of LINC00470 in the mice models, as well as in the KCL22 and K562 cells. LINC00470 was significantly enriched for PTEN mRNA to exhibit a negative regulatory relationship between LINC00470 and PTEN mRNA. However, the alteration of LINC00470 had no effect on the luciferase activity of PTEN promoter, while the half-life of PTEN mRNA was affected. It was further validated that LINC00470 down-regulated PTEN expression by positively regulating the m6A modification of PTEN mRNA via RNA methyltransferase METTL3. Moreover, the relative expression of LC3II, Beclin-1, ATG7 and ATG5 was all decreased in cells treated with LINC00470, and down-regulated PTEN expression was observed in chemo-resistant cells, while the expression of PTEN was rescued by the transfection of shMETTL3 into chemo-resistant cells. Moreover, the knockdown of METTL3 also restored the normal level of PTEN m⁶ A modification and LINC00470 expression in chemo-resistant cells. In conclusion, our results demonstrated the molecular mechanism underlying the effect of LINC00470 on CML by reducing the PTEN stability via RNA methyltransferase METTL3, thus leading to the inhibition of cell autophagy while promoting chemoresistance in CML.

Comprehensive in silico mutational-sensitivity analysis of PTEN establishes signature regions implicated in pathogenesis of Autism Spectrum Disorders

An extensively studied cancer and Autism Spectrum Disorders (ASD) gene like PTEN provided an exclusive opportunity to map its mutational-landscape, compare and establish plausible genotypic predictors of ASD-associated phenotypic outcomes. Our exhaustive in silico analysis on 4252 SNPs using >30 tools identified increased mutational-density in exon7. Phosphatase domain, although evolutionarily conserved, had the most nsSNPs localised within signature regions. The evolutionarily variable C-terminal side contained the highest truncating-SNPs outside signature regions of C2 domain and most PTMs within C-tail site which displayed maximum intolerance to polymorphisms, and permitted benign but destabilising nsSNPs that enhanced its intrinsically-disordered nature. ASD-associated SNPs localised within ATP-binding motifs and Nuclear-Localising-Sequences were the most potent triggers of ASD manifestation. These, along with variations within P, WPD and TI loops, M1 within phosphatase domain, M2 and MoRFs of C2 domain, caused severe long-range conformational fluctuations altering PTEN's dynamic stability- not observed in variations outside signature regions. 3'UTR-SNPs affected 44 strong miRNA brain-specific targets; several 5' UTR-SNPs targeted transcription-factor POLR2A and 10 pathogenic Splice-Affecting-Variants were identified.

Structural Mechanisms of PTEN Regulation

The tumor suppressor phosphatase and tensin homolog on chromosome 10 (PTEN) is a tightly regulated enzyme responsible for dephosphorylating the progrowth lipid messenger molecule phosphatidylinositol 3,4,5-trisphosphate (PIP₃) on the plasma membrane. The carboxy-terminal tail (CTT) of PTEN is key for regulation of the enzyme. When phosphorylated, the unstructured CTT interacts with the phosphatase-C2 superdomain to inactivate the enzyme by preventing membrane association. PTEN mutations associated with cancer also inactivate the enzyme. Alternate translation-initiation sites generate extended isoforms of PTEN, such as PTEN-L that has multiple roles in cells. The extended amino-terminal region bears a signal sequence and a polyarginine sequence to facilitate exit from and entry into cells, respectively, and a membrane-binding helix that activates the enzyme. This amino-terminal region also facilitates mitochondrial and nucleolar localization. This review explores PTEN structure and its impact on localization and regulation.

Characterization of Specific Ion Effects on PI(4,5)P2 Clustering: Molecular Dynamics Simulations and Graph-Theoretic Analysis

Numerous cellular functions mediated by phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2; PIP2) involve clustering of the lipid as well as colocalization with other lipids. Although the cation-mediated electrostatic interaction is regarded as the primary clustering mechanism, the ion-specific nature of the intermolecular network formation makes it challenging to characterize the clusters. Here we use all-atom molecular dynamics (MD) simulations of PIP2 monolayers and graph-theoretic analysis to gain insight into the phenomenon. MD simulations reveal that the intermolecular interactions preferentially occur between specific cations and phosphate groups (P1, P4, and P5) of the inositol headgroup with better-matched kosmotropic/chaotropic characters consistent with the law of matching water affinities (LMWA). Ca2+ is strongly attracted to P4/P5, while K+ preferentially binds to P1; Na+ interacts with both P4/P5 and P1. These specific interactions lead to the characteristic clustering patterns. Specificially, the size distributions and structures of PIP2 clusters generated by kosmotropic cations Ca2+ and Na+ are bimodal, with a combination of small and large clusters, while there is little clustering in the presence of only chaotropic K+; the largest clusters are obtained in systems with all three cations. The small-world network (a model with both local and long-range connections) best characterizes the clusters, followed by the random and the scale-free networks. More generally, the present results interpreted within the LMWA are consistent with the relative eukaryotic intracellular concentrations Ca2+ ≪ Na+ < Mg2+ < K+; that is, concentrations of Ca2+ and Na+ must be low to prevent damaging aggregation of lipids, DNA, RNA and phosphate-containing proteins.

Precise Immunodetection of PTEN Protein in Human Neoplasia

PTEN is a major tumor-suppressor protein whose expression and biological activity are frequently diminished in sporadic or inherited cancers. PTEN gene deletion or loss-of-function mutations favor tumor cell growth and are commonly found in clinical practice. In addition, diminished PTEN protein expression is also frequently observed in tumor samples from cancer patients in the absence of PTEN gene alterations. This makes PTEN protein levels a potential biomarker parameter in clinical oncology, which can guide therapeutic decisions. The specific detection of PTEN protein can be achieved by using highly defined anti-PTEN monoclonal antibodies (mAbs), characterized with precision in terms of sensitivity for the detection technique, specificity for PTEN binding, and constraints of epitope recognition. This is especially relevant taking into consideration that PTEN is highly targeted by mutations and posttranslational modifications, and different PTEN protein isoforms exist. The precise characterization of anti-PTEN mAb reactivity is an important step in the validation of these reagents as diagnostic and prognostic tools in clinical oncology, including their routine use in analytical immunohistochemistry (IHC). Here, we review the current status on the use of well-defined anti-PTEN mAbs for PTEN immunodetection in the clinical context and discuss their potential usefulness and limitations for a more precise cancer diagnosis and patient benefit.

Expression of Human PTEN-L in a Yeast Heterologous Model Unveils Specific N-Terminal Motifs Controlling PTEN-L Subcellular Localization and Function

The tumour suppressor PTEN is frequently downregulated, mutated or lost in several types of tumours and congenital disorders including PHTS (PTEN Hamartoma Tumour Syndrome) and ASD (Autism Spectrum Disorder). PTEN is a lipid phosphatase whose activity over the lipid messenger PIP₃ counteracts the stimulation of the oncogenic phosphatidylinositol 3-kinase (PI3K) pathway. Recently, several extended versions of PTEN produced in the cell by alternative translation initiation have been described, among which, PTEN-L and PTEN-M represent the longest isoforms. We previously developed a humanized yeast model in which the expression of PI3K in Saccharomyces cerevisiae led to growth inhibition that could be suppressed by co-expression of PTEN. Here, we show that the expression of PTEN-L and PTEN-M in yeast results in robust counteracting of PI3K-dependent growth inhibition. N-terminally tagged GFP-PTEN-L was sharply localized at the yeast plasma membrane. Point mutations of a putative membrane-binding helix located at the PTEN-L extension or its deletion shifted localization to nuclear. Also, a shift from plasma membrane to nucleus was observed in mutants at basic amino acid clusters at the PIP₂-binding motif, and at the Cα2 and CBR3 loops at the C2 domain. In contrast, C-terminally tagged PTEN-L-GFP displayed mitochondrial localization in yeast, which was shifted to plasma membrane by removing the first 22 PTEN-L residues. Our results suggest an important role of the N-terminal extension of alternative PTEN isoforms on their spatial and functional regulation.

PTEN in Lung Cancer: Dealing with the Problem, Building on New Knowledge and Turning the Game Around

Lung cancer is the most common malignancy and cause of cancer deaths worldwide, owing to the dismal prognosis for most affected patients. Phosphatase and tensin homolog deleted in chromosome 10 (PTEN) acts as a powerful tumor suppressor gene and even partial reduction of its levels increases cancer susceptibility. While the most validated anti-oncogenic duty of PTEN is the negative regulation of the PI3K/mTOR/Akt oncogenic signaling pathway, further tumor suppressor functions, such as chromosomal integrity and DNA repair have been reported. PTEN protein loss is a frequent event in lung cancer, but genetic alterations are not equally detected. It has been demonstrated that its expression is regulated at multiple genetic and epigenetic levels and deeper delineation of these mechanisms might provide fertile ground for upgrading lung cancer therapeutics. Today, PTEN expression is usually determined by immunohistochemistry and low protein levels have been associated with decreased survival in lung cancer. Moreover, available data involve PTEN mutations and loss of activity with resistance to targeted treatments and immunotherapy. This review discusses the current knowledge about PTEN status in lung cancer, highlighting the prevalence of its alterations in the disease, the regulatory mechanisms and the implications of PTEN on available treatment options.

Bone metastases from a 1p/19q codeleted and IDH1-mutant anaplastic oligodendroglioma: a case report

BACKGROUND

Oligodendroglioma is a rare type of primary brain tumor which, like other malignant gliomas, metastasizes very rarely even when in high-grade form.

CASE REPORT

A 36-year-old white man diagnosed 29 months previously as having 1p/19q codeleted anaplastic oligodendroglioma presented bilateral cruralgia and lower limb motor deficits. A computed tomography scan showed multiple osteoblastic bone lesions. The presence of oligodendroglial cells was revealed by bone marrow biopsy and confirmed by immunohistochemical analyses. A positon emission tomography-computed tomography scan confirmed the exclusive involvement of bones.

CONCLUSION

This case joins less than 20 other reported cases of oligodendroglioma bone marrow metastasis, and is one of only a handful of cases of diffuse bone metastases beyond the axial skeleton. To the best of our knowledge, the early relapse of 1p/19q codeleted anaplastic oligodendroglioma with this distribution of metastases has never been described in the literature.

Precise definition of PTEN C-terminal epitopes and its implications in clinical oncology

Anti-PTEN monoclonal antibodies (mAb) are arising as important tools for immunohistochemistry (IHC) and protein quantification routine analysis in clinical oncology. Although an effort has been made to document the reliability of tumor tissue section immunostaining by anti-PTEN mAb, and to standardize their IHC use in research and in the clinical practice, the precise topological and biochemical definition of the epitope recognized by each mAb has been conventionally overlooked. In this study, six commercial anti-PTEN mAb have been validated and characterized for sensitivity and specificity by IHC and FISH, using a set of prostate and urothelial bladder tumor specimens, and by immunoblot, using PTEN positive and PTEN negative human cell lines. Immunoblot precise epitope mapping, performed using recombinant PTEN variants and mutations, revealed that all mAb recognized linear epitopes of 6–11 amino acid length at the PTEN C-terminus. Tumor-associated or disease-associated mutations at the PTEN C-terminus did not affect subcellular localization or PIP3 phosphatase activity of PTEN in cells, although resulted in specific loss of reactivity for some mAb. Furthermore, specific mimicking-phosphorylation mutations at the PTEN C-terminal region also abolished binding of specific mAb. Our study adds new evidence on the relevance of a precise epitope mapping in the validation of anti-PTEN mAb for their use in the clinics. This will be substantial to provide a more accurate diagnosis in clinical oncology based on PTEN protein expression in tumors and biological fluids.

Mechanisms of PTEN loss in cancer: It's all about diversity

PTEN is a phosphatase which metabolises PIP₃, the lipid product of PI 3-Kinase, directly opposing the activation of the oncogenic PI3K/AKT/mTOR signalling network. Accordingly, loss of function of the PTEN tumour suppressor is one of the most common events observed in many types of cancer. Although the mechanisms by which PTEN function is disrupted are diverse, the most frequently observed events are deletion of a single gene copy of PTEN and gene silencing, usually observed in tumours with little or no PTEN protein detectable by immunohistochemistry. Accordingly, with the exceptions of glioblastoma and endometrial cancer, mutations of the PTEN coding sequence are uncommon (<10%) in most types of cancer. Here we review the data relating to PTEN loss in seven common tumour types and discuss mechanisms of PTEN regulation, some of which appear to contribute to reduced PTEN protein levels in cancers.

PTEN-L is a novel protein phosphatase for ubiquitin dephosphorylation to inhibit PINK1-Parkin-mediated mitophagy

Mitophagy is an important type of selective autophagy for specific elimination of damaged mitochondria. PTEN-induced putative kinase protein 1 (PINK1)-catalyzed phosphorylation of ubiquitin (Ub) plays a critical role in the onset of PINK1-Parkin-mediated mitophagy. Phosphatase and tensin homolog (PTEN)-long (PTEN-L) is a newly identified isoform of PTEN, with addition of 173 amino acids to its N-terminus. Here we report that PTEN-L is a novel negative regulator of mitophagy via its protein phosphatase activity against phosphorylated ubiquitin. We found that PTEN-L localizes at the outer mitochondrial membrane (OMM) and overexpression of PTEN-L inhibits, whereas deletion of PTEN-L promotes, mitophagy induced by various mitochondria-damaging agents. Mechanistically, PTEN-L is capable of effectively preventing Parkin mitochondrial translocation, reducing Parkin phosphorylation, maintaining its closed inactive conformation, and inhibiting its E3 ligase activity. More importantly, PTEN-L reduces the level of phosphorylated ubiquitin (pSer65-Ub) in vivo, and in vitro phosphatase assay confirms that PTEN-L dephosphorylates pSer65-Ub via its protein phosphatase activity, independently of its lipid phosphatase function. Taken together, our findings demonstrate a novel function of PTEN-L as a protein phosphatase for ubiquitin, which counteracts PINK1-mediated ubiquitin phosphorylation leading to blockage of the feedforward mechanisms in mitophagy induction and eventual suppression of mitophagy. Thus, understanding this novel function of PTEN-L provides a key missing piece in the molecular puzzle controlling mitophagy, a critical process in many important human diseases including neurodegenerative disorders such as Parkinson's disease.

Overexpressing TPTE2 (TPIP), a homolog of the human tumor suppressor gene PTEN, rescues the abnormal phenotype of the PTEN-/- mutant

One possible approach to normalize mutant cells that are metastatic and tumorigenic, is to upregulate a functionally similar homolog of the mutated gene. Here we have explored this hypothesis by generating an overexpressor of TPTE2 (TPIP), a homolog of PTEN, in PTEN-/- mutants, the latter generated by targeted mutagenesis of a human epithelial cell line. Overexpression of TPTE2 normalized phenotypic changes associated with the PTEN mutation. The PTEN-/- -associated changes rescued by overexpressing TPTE2 included 1) accelerated wound healing in the presence or absence of added growth factors (GFs), 2) increased division rates on a 2D substrate in the presence of GFs, 3) adhesion and viability on a 2D substrate in the absence of GFs, 4) viability in a 3D Matrigel model in the absence of GFs and substrate adhesion 5) loss of apoptosis-associated annexin V cell surface binding sites. The results justify further exploration into the possibility that upregulating TPTE2 by a drug may reverse metastatic and tumorigenic phenotypes mediated in part by a mutation in PTEN. This strategy may also be applicable to other tumorigenic mutations in which a homolog to the mutated gene is present and can substitute functionally.

Graph-Theoretic Analysis of Monomethyl Phosphate Clustering in Ionic Solutions

All-atom molecular dynamics simulations combined with graph-theoretic analysis reveal that clustering of monomethyl phosphate dianion (MMP^2-) is strongly influenced by the types and combinations of cations in the aqueous solution. Although Ca²⁺ promotes the formation of stable and large MMP^2- clusters, K⁺ alone does not. Nonetheless, clusters are larger and their link lifetimes are longer in mixtures of K⁺ and Ca²⁺. This "synergistic" effect depends sensitively on the Lennard-Jones interaction parameters between Ca²⁺ and the phosphorus oxygen and correlates with the hydration of the clusters. The pronounced MMP^2- clustering effect of Ca²⁺ in the presence of K⁺ is confirmed by Fourier transform infrared spectroscopy. The characterization of the cation-dependent clustering of MMP^2- provides a starting point for understanding cation-dependent clustering of phosphoinositides in cell membranes.

PTEN: Tumor Suppressor and Metabolic Regulator

Phosphatase and Tensin Homolog deleted on Chromosome 10 (PTEN) is a dual phosphatase with both protein and lipid phosphatase activities. PTEN was first discovered as a tumor suppressor with growth and survival regulatory functions. In recent years, the function of PTEN as a metabolic regulator has attracted significant attention. As the lipid phosphatase that dephosphorylates phosphatidylinositol-3, 4, 5-phosphate (PIP₃), PTEN reduces the level of PIP₃, a critical 2nd messenger mediating the signal of not only growth factors but also insulin. In this review, we introduced the discovery of PTEN, the PTEN-regulated canonical and nuclear signals, and PTEN regulation. We then focused on the role of PTEN and PTEN-regulated signals in metabolic regulation. This included the role of PTEN in glycolysis, gluconeogenesis, glycogen synthesis, lipid metabolism as well as mitochondrial metabolism. We also included how PTEN and PTEN regulated metabolic functions may act paradoxically toward insulin sensitivity and tumor metabolism and growth. Further understanding of how PTEN regulates metabolism and how such regulations lead to different biological outcomes is necessary for interventions targeting at the PTEN-regulated signals in either cancer or diabetes treatment.

Engineering PTEN-L for Cell-Mediated Delivery

The tumor suppressor PTEN is frequently inactivated in glioblastoma. PTEN-L is a long form of PTEN produced by translation from an alternate upstream start codon. Unlike PTEN, PTEN-L has a signal sequence and a tract of six arginine residues that allow PTEN-L to be secreted from cells and be taken up by neighboring cells. This suggests that PTEN-L could be used as a therapeutic to restore PTEN activity. However, effective delivery of therapeutic proteins to treat CNS cancers such as glioblastoma is challenging. One method under evaluation is cell-mediated therapy, where cells with tumor-homing abilities such as neural stem cells are genetically modified to express a therapeutic protein. Here, we have developed a version of PTEN-L that is engineered for enhanced cell-mediated delivery. This was accomplished by replacement of the native leader sequence of PTEN-L with a leader sequence from human light-chain immunoglobulin G (IgG). This version of PTEN-L showed increased secretion and an increased ability to transfer to neighboring cells. Neural stem cells derived from human fibroblasts could be modified to express this version of PTEN-L and were able to deliver catalytically active light-chain leader PTEN-L (lclPTEN-L) to neighboring glioblastoma cells.

PTEN proteoforms in biology and disease

Proteoforms are specific molecular forms of protein products arising from a single gene that possess different structures and different functions. Therefore, a single gene can produce a large repertoire of proteoforms by means of allelic variations (mutations, indels, SNPs), alternative splicing and other pre-translational mechanisms, post-translational modifications (PTMs), conformational dynamics, and functioning. Resulting proteoforms that have different sizes, alternative splicing patterns, sets of post-translational modifications, protein-protein interactions, and protein-ligand interactions, might dramatically increase the functionality of the encoded protein. Herein, we have interrogated the tumor suppressor PTEN for its proteoforms and find that this protein exists in multiple forms with distinct functions and sub-cellular localizations. Furthermore, the levels of each PTEN proteoform in a given cell may affect its biological function. Indeed, the paradigm of the continuum model of tumor suppression by PTEN can be better explained by the presence of a continuum of PTEN proteoforms, diversity, and levels of which are associated with pathological outcomes than simply by the different roles of mutations in the PTEN gene. Consequently, understanding the mechanisms underlying the dysregulation of PTEN proteoforms by several genomic and non-genomic mechanisms in cancer and other diseases is imperative. We have identified different PTEN proteoforms, which control various aspects of cellular function and grouped them into three categories of intrinsic, function-induced, and inducible proteoforms. A special emphasis is given to the inducible PTEN proteoforms that are produced due to alternative translational initiation. The novel finding that PTEN forms dimers with biological implications supports the notion that PTEN proteoform-proteoform interactions may play hitherto unknown roles in cellular homeostasis and in pathogenic settings, including cancer. These PTEN proteoforms with unique properties and functionalities offer potential novel therapeutic opportunities in the treatment of various cancers and other diseases.

Ribosome Footprint Profiling of Translation throughout the Genome

Ribosome profiling has emerged as a technique for measuring translation comprehensively and quantitatively by deep sequencing of ribosome-protected mRNA fragments. By identifying the precise positions of ribosomes, footprinting experiments have unveiled key insights into the composition and regulation of the expressed proteome, including delineating potentially functional micropeptides, revealing pervasive translation on cytosolic RNAs, and identifying differences in elongation rates driven by codon usage or other factors. This Primer looks at important experimental and analytical concerns for executing ribosome profiling experiments and surveys recent examples where the approach was developed to explore protein biogenesis and homeostasis.

Systematic analysis of the PTEN 5' leader identifies a major AUU initiated proteoform

Abundant evidence for translation within the 5' leaders of many human genes is rapidly emerging, especially, because of the advent of ribosome profiling. In most cases, it is believed that the act of translation rather than the encoded peptide is important. However, the wealth of available sequencing data in recent years allows phylogenetic detection of sequences within 5' leaders that have emerged under coding constraint and therefore allow for the prediction of functional 5' leader translation. Using this approach, we previously predicted a CUG-initiated, 173 amino acid N-terminal extension to the human tumour suppressor PTEN. Here, a systematic experimental analysis of translation events in the PTEN 5' leader identifies at least two additional non-AUG-initiated PTEN proteoforms that are expressed in most human cell lines tested. The most abundant extended PTEN proteoform initiates at a conserved AUU codon and extends the canonical AUG-initiated PTEN by 146 amino acids. All N-terminally extended PTEN proteoforms tested retain the ability to downregulate the PI3K pathway. We also provide evidence for the translation of two conserved AUG-initiated upstream open reading frames within the PTEN 5' leader that control the ratio of PTEN proteoforms.

PTEN: a yin-yang master regulator protein in health and disease

The PTEN gene is a tumor suppressor gene frequently mutated in human tumors, which encodes a ubiquitous protein whose major activity is to act as a lipid phosphatase that counteracts the action of the oncogenic PI3K. In addition, PTEN displays protein phosphatase- and catalytically-independent activities. The physiologic control of PTEN function, and its inactivation in cancer and other human diseases, including some neurodevelopmental disorders, is upon the action of multiple regulatory mechanisms. This provides a wide spectrum of potential therapeutic approaches to reconstitute PTEN activity. By contrast, inhibition of PTEN function may be beneficial in a different group of human diseases, such as type 2 diabetes or neuroregeneration-related pathologies. This makes PTEN a functionally dual yin-yang protein with high potential in the clinics. Here, a brief overview on PTEN and its relation with human disease is presented.

Immunopathologic Assessment of PTEN Expression

Immunohistochemistry (IHC) is an excellent technique used routinely to define the phenotype in pathology laboratories through the analysis of molecular expression in cells and tissues. The PTEN protein is ubiquitously expressed in the majority of human tissues, and allelic or complete loss of PTEN is frequently observed in different types of malignancies leading to an activation of the AKT/mTOR pathways. IHC-based analyses are best to determine the level of PTEN expression in histological samples, but not to assess partial or heterozygous deletions, for which FISH analyses are more appropriate. Interpretation of the IHC results is the most critical point in the assessment of PTEN expression, since it is used both as a prognostic factor and as a tool to guide therapeutic intervention and response to therapy. Importantly, analyses of well-known downstream markers, such as AKT or mTOR, may be used to further analyze PTEN functional status.

PTEN at 18: Still Growing

Discovered in 1997, PTEN remains one of the most studied tumor suppressors. In this issue of Methods in Molecular Biology, we assembled a series of papers describing various clinical and experimental approaches to studying PTEN function. Due to its broad expression, regulated subcellular localization, and intriguing phosphatase activity, methodologies aimed at PTEN study have often been developed in the context of mutations affecting various aspects of its regulation, found in patients burdened with PTEN loss-driven tumors. PTEN's extensive posttranslational modifications and dynamic localization pose unique challenges for studying PTEN features in isolation and necessitate considerable development of experimental systems to enable controlled characterization. Nevertheless, ongoing efforts towards the development of PTEN knockout and knock-in animals and cell lines, antibodies, and enzymatic assays have facilitated a huge body of work, which continues to unravel the fascinating biology of PTEN.

Methods in the Study of PTEN Structure: X-Ray Crystallography and Hydrogen Deuterium Exchange Mass Spectrometry

Despite its small size and deceptively simple domain organization, PTEN remains a challenging structural target due to its N- and C-terminal intrinsically disordered segments, and the conformational heterogeneity caused by phosphorylation of its C terminus. Using hydrogen/deuterium exchange mass spectrometry (HDX-MS), it is possible to probe the conformational dynamics of the disordered termini, and also to determine how PTEN binds to lipid membranes. Here, we describe how to purify recombinant, homogenously dephosphorylated PTEN from a eukaryotic system for subsequent investigation with HDX-MS or crystallography.

Methods to Study PTEN in Mitochondria and Endoplasmic Reticulum

Although PTEN has been widely described as a nuclear and cytosolic protein, in the last 2 years, alternative organelles, such as the endoplasmic reticulum (ER), pure mitochondria, and mitochondria-associated membranes (MAMs), have been recognized as pivotal targets of PTEN activity.Here, we describe different methods that have been used to highlight PTEN subcellular localization.First, a protocol to extract nuclear and cytosolic fractions has been described to assess the "canonical" PTEN localization. Moreover, we describe a protocol for mitochondria isolation with proteinase K (PK) to further discriminate whether PTEN associates with the outer mitochondrial membrane (OMM) or resides within the mitochondria. Finally, we focus our attention on a subcellular fractionation protocol of cells that permits the isolation of MAMs containing unique regions of ER membranes attached to the outer mitochondrial membrane (OMM) and mitochondria without contamination from other organelles. In addition to biochemical fractionations, immunostaining can be used to determine the subcellular localization of proteins; thus, a detailed protocol to obtain good immunofluorescence (IF) is described. The employment of these methodological approaches could facilitate the identification of different PTEN localizations in several physiopathological contexts.

The intrinsically disordered tails of PTEN and PTEN-L have distinct roles in regulating substrate specificity and membrane activity

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a lipid and protein phosphatase, and both activities are necessary for its role as a tumour suppressor. PTEN activity is controlled by phosphorylation of its intrinsically disordered C-terminal tail. A recently discovered variant of PTEN, PTEN-long (PTEN-L), has a 173-residue N-terminal extension that causes PTEN-L to exhibit unique behaviour, such as movement from one cell to another. Using hydrogen/deuterium exchange mass spectrometry (HDX-MS) and biophysical assays, we show that both the N-terminal extension of PTEN-L and C-terminal tail of PTEN affect the phosphatase activity using unique mechanisms. Phosphorylation of six residues in the C-terminal tail of PTEN results in auto-inhibitory interactions with the phosphatase and C2 domains, effectively blocking both the active site and the membrane-binding interface of PTEN. Partially dephosphorylating PTEN on pThr(366)/pSer(370) results in sufficient exposure of the active site to allow a selective activation for soluble substrates. Using HDX-MS, we identified a membrane-binding element in the N-terminal extension of PTEN-L, termed the membrane-binding helix (MBH). The MBH radically alters the membrane binding mechanism of PTEN-L compared with PTEN, switching PTEN-L to a 'scooting' mode of catalysis from the 'hopping' mode that is characteristic of PTEN.

Balancing Proliferation and Connectivity in PTEN-associated Autism Spectrum Disorder

Germline mutations in PTEN, which encodes a widely expressed phosphatase, was mapped to 10q23 and identified as the susceptibility gene for Cowden syndrome, characterized by macrocephaly and high risks of breast, thyroid, and other cancers. The phenotypic spectrum of PTEN mutations expanded to include autism with macrocephaly only 10 years ago. Neurological studies of patients with PTEN-associated autism spectrum disorder (ASD) show increases in cortical white matter and a distinctive cognitive profile, including delayed language development with poor working memory and processing speed. Once a germline PTEN mutation is found, and a diagnosis of phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome made, the clinical outlook broadens to include higher lifetime risks for multiple cancers, beginning in childhood with thyroid cancer. First described as a tumor suppressor, PTEN is a major negative regulator of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (mTOR) signaling pathway-controlling growth, protein synthesis, and proliferation. This canonical function combines with less well-understood mechanisms to influence synaptic plasticity and neuronal cytoarchitecture. Several excellent mouse models of Pten loss or dysfunction link these neural functions to autism-like behavioral abnormalities, such as altered sociability, repetitive behaviors, and phenotypes like anxiety that are often associated with ASD in humans. These models also show the promise of mTOR inhibitors as therapeutic agents capable of reversing phenotypes ranging from overgrowth to low social behavior. Based on these findings, therapeutic options for patients with PTEN hamartoma tumor syndrome and ASD are coming into view, even as new discoveries in PTEN biology add complexity to our understanding of this master regulator.

Molecular pathways: intercellular PTEN and the potential of PTEN restoration therapy

Phosphatase and Tensin homolog deleted on chromosome Ten (PTEN) acts as a tumor suppressor through both PI3K-dependent and -independent mechanisms. Reduced PTEN activity has been shown to affect not only tumor cell proliferation and survival but also the microenvironmental context in which nascent tumors develop. As a result of the multifaceted tumor-suppressive roles of PTEN, tumors evolve by selecting for clones in which PTEN activity is lost. PTEN activity within tumors can be modulated in numerous ways, including direct mutation, epigenetic regulation, and amplification or mutation of other proteins that can regulate or degrade PTEN. These events functionally prevent PTEN protein from acting within tumor cells. Paracrine roles for PTEN gene products (exosomal PTEN and PTEN-L) have recently been identified, through which PTEN gene products produced in one cell are able to enter recipient cells and contribute to PTEN functions. In preclinical models purified PTEN-L protein was able to enter tumor xenografts and downregulate PI3K signaling as well as cause tumor cell death. Here, we review the role of PTEN as a multifaceted tumor suppressor and reflect upon the potential for PTEN restoration therapy.

Kinases, tails and more: regulation of PTEN function by phosphorylation

Phosphorylation regulates the conformation, stability, homo- and heterotypic protein interactions, localization, and activity of the tumor suppressor PTEN. From a simple picture, at the beginning of this millennium, recognizing that CK2 phosphorylated PTEN at the C-terminus and thereby impacted on PTEN stability and activity, research has led to a significantly more complex scenario today, where for instance GSK3, Plk3, ATM, ROCK or Src-family kinases are also gaining the spotlight in this evolving play. Here, we review the current knowledge on the kinases that phosphorylate PTEN, and on the impact that specific phosphorylation events have on PTEN function.

A functional dissection of PTEN N-terminus: implications in PTEN subcellular targeting and tumor suppressor activity

Spatial regulation of the tumor suppressor PTEN is exerted through alternative plasma membrane, cytoplasmic, and nuclear subcellular locations. The N-terminal region of PTEN is important for the control of PTEN subcellular localization and function. It contains both an active nuclear localization signal (NLS) and an overlapping PIP2-binding motif (PBM) involved in plasma membrane targeting. We report a comprehensive mutational and functional analysis of the PTEN N-terminus, including a panel of tumor-related mutations at this region. Nuclear/cytoplasmic partitioning in mammalian cells and PIP3 phosphatase assays in reconstituted S. cerevisiae defined categories of PTEN N-terminal mutations with distinct PIP3 phosphatase and nuclear accumulation properties. Noticeably, most tumor-related mutations that lost PIP3 phosphatase activity also displayed impaired nuclear localization. Cell proliferation and soft-agar colony formation analysis in mammalian cells of mutations with distinctive nuclear accumulation and catalytic activity patterns suggested a contribution of both properties to PTEN tumor suppressor activity. Our functional dissection of the PTEN N-terminus provides the basis for a systematic analysis of tumor-related and experimentally engineered PTEN mutations.

Relevance and therapeutic possibility of PTEN-long in renal cell carcinoma

PTEN-Long is a translational variant of PTEN (Phosphatase and Tensin Homolog). Like PTEN, PTEN-Long is able to antagonize the PI3K-Akt pathway and inhibits tumor growth. In this study, we investigated the role PTEN-Long plays in the development and progression of clear cell renal cell carcinoma (ccRCC) and explored the therapeutic possibility using proteinaceous PTEN-Long to treat ccRCC. We found that the protein levels of PTEN-Long were drastically reduced in ccRCC, which was correlated with increased levels of phosphorylated Akt (pAkt). Gain of function experiments showed overexpression of PTEN-Long in the ccRCC cell line 786-0 suppressed PI3K-Akt signaling, inhibited cell proliferation, migration and invasion, and eventually induced cell death. When purified PTEN-Long was added into cultured 786-0 cells, it entered cells, blocked Akt activation, and induced apoptosis involving Caspase 3 cleavage. Furthermore, PTEN-Long inhibited proliferation of 786-0 cells in xenograft mouse model. Our results implicated that understanding the roles of PTEN-Long in renal cell carcinogenesis has therapeutic significance.

Conformational stability and catalytic activity of PTEN variants linked to cancers and autism spectrum disorders

Phosphoinositides are membrane components that play critical regulatory roles in mammalian cells. The enzyme PTEN, which catalyzes the dephosphorylation of the phosphoinositide PIP3, is damaged in most sporadic tumors. Mutations in the PTEN gene have also been linked to autism spectrum disorders and other forms of delayed development. Here, human PTEN is shown to be on the cusp of unfolding under physiological conditions. Variants of human PTEN linked to somatic cancers and disorders on the autism spectrum are shown to be impaired in their conformational stability, catalytic activity, or both. Those variants linked only to autism have activity higher than the activity of those linked to cancers. PTEN-L, which is a secreted trans-active isoform, has conformational stability greater than that of the wild-type enzyme. These data indicate that PTEN is a fragile enzyme cast in a crucial role in cellular metabolism and suggest that PTEN-L is a repository for a critical catalytic activity.

Catalysis by the tumor-suppressor enzymes PTEN and PTEN-L

Phosphatase and tensin homologue deleted from chromosome ten (PTEN) is a lipid phosphatase tumor suppressor that is lost or inactivated in most human tumors. The enzyme catalyzes the hydrolysis of phosphatidylinositol-(3,4,5)-trisphosphate (PIP₃) to form phosphatidylinositol-(4,5)-bisphosphate (PIP₂) and inorganic phosphate. Here, we report on the first continuous assay for the catalytic activity of PTEN. Using this assay, we demonstrate that human PTEN is activated by the reaction product PIP₂, as well as in solutions of low salt concentration. This activation is abrogated in the K13A variant, which has a disruption in a putative binding site for PIP₂. We also demonstrate that PTEN-L, which derives from alternative translation of the PTEN mRNA, is activated constitutively. These findings have implications for catalysis by PTEN in physiological environments and could expedite the development of PTEN-based chemotherapeutic agents.

C. elegans as a model to study PTEN's regulation and function

PTEN (phosphatase and tensin homolog deleted on chromosome 10) has important roles in tumor suppression, metabolism, and development, yet its regulators, effectors, and functions are not fully understood. DAF-18 is the PTEN ortholog in Caenorhabditis elegans. DAF-18's role is highly conserved to human PTEN, and can be functionally replaced by human PTEN. Thus C. elegans provides a valuable model to study PTEN. This review assesses current and emerging methods to study DAF-18's regulators and functions in C. elegans. We propose genetic modify screens to identify genes that interact with daf-18/PTEN. These genes are potential targets for anticancer drug therapies. We also provide a review on the roles DAF-18/PTEN has during C. elegans development and how studying these physiological roles can provide mechanistic insight on DAF-18/PTEN function.

The mitochondrial permeability transition pore and cancer: molecular mechanisms involved in cell death

Since its discovery in the 1970s, the mitochondrial permeability transition (MPT) has been proposed to be a strategic regulator of cell death. Intense research efforts have focused on elucidating the molecular components of the MPT because this knowledge may help to better understand and treat various pathologies ranging from neurodegenerative and cardiac diseases to cancer. In the case of cancer, several studies have revealed alterations in the activity of the mitochondrial permeability transition pore (mPTP) and have determined its regulatory mechanism; these studies have also suggested that suppression of the activity of the mPTP, rather than its inactivation, commonly occurs in solid neoplasms. This review focuses on the most recent advances in understanding mPTP regulation in cancer and highlights the ability of the mPTP to impede the mechanisms of cell death.

Analysis of intracellular PTEN signaling and secretion

The tumor suppressor PTEN dephosphorylates PIP3 to inhibit PI3K signaling in cells. Altering PTEN intracellular signaling can therefore significantly affect cell behavior. Two novel mechanisms of PTEN regulation including the secretion and entry of the translational variant PTEN-L, and enzymatic inhibition by the interacting protein P-REX2, have been shown to modulate PI3K signaling, cellular proliferation and survival, and glucose metabolism. Here, we review the methods used to identify and validate the existence of both PTEN-L and the P-REX2-PTEN complex, to determine their effects on PTEN phosphatase activity, and to examine their role in cellular physiology.

Pten function in zebrafish: anything but a fish story

Zebrafish is an excellent model system for the analysis of gene function. We and others use zebrafish to investigate the function of the tumor suppressor, Pten, in tumorigenesis and embryonic development. Zebrafish have two pten genes, ptena and ptenb. The recently identified N-terminal extension of human PTEN that may facilitate cell membrane transfer, appears not to be conserved in zebrafish Ptena or Ptenb. Mutants that retain a single wild type pten allele develop tumors, predominantly hemangiosarcomas. Homozygous double mutants are embryonic lethal. Zebrafish embryos lacking functional Pten display enhanced proliferation of endothelial cells, resulting in hyperbranching of blood vessels. In addition, ptena-/-ptenb-/- mutant embryos display enhanced proliferation of hematopoietic stem and progenitor cells and concomitant arrest of differentiation, although Pten-deficient cells commit to all blood cell lineages. Zebrafish is an ideal model for intravital imaging and future work using ptena-/-ptenb-/- mutants will enhance our understanding of the function of Pten in vivo.

Yeast-based methods to assess PTEN phosphoinositide phosphatase activity in vivo

The PTEN phosphoinositide 3-phosphatase is a tumor suppressor commonly targeted by pathologic missense mutations. Subject to multiple complex layers of regulation, its capital role in cancer relies on its counteracting function of class I phosphoinositide 3-kinase (PI3K), a key feature in oncogenic signaling pathways. Precise assessment of the involvement of PTEN mutations described in the clinics in loss of catalytic activity requires either tedious in vitro phosphatase assays or in vivo experiments involving transfection into mammalian cell lines. Taking advantage of the versatility of the model organism Saccharomyces cerevisiae, we have developed different functional assays by reconstitution of the mammalian PI3K-PTEN switch in this lower eukaryote. This methodology is based on the fact that regulated PI3K expression in yeast cells causes conversion of PtdIns(4,5)P2 in PtdIns(3,4,5)P3 and co-expression of PTEN counteracts this effect. This can be traced by monitoring growth, given that PtdIns(4,5)P2 pools are essential for the yeast cell, or by using fluorescent reporters amenable for microscopy or flow cytometry. Here we describe the methodology and review its application to evaluate the functionality of PTEN mutations. We show that the technique is amenable to both directed and systematic structure-function relationship studies, and present an example of its use for the study of the recently discovered PTEN-L variant.

Study of PTEN subcellular localization

The tumor suppressor PTEN is a key regulator of a plethora of cellular processes that are crucial in cancer development. Through its lipid phosphatase activity PTEN suppresses the PI3K/AKT pathway to govern cell proliferation, growth, migration, energy metabolism and death. The repertoire of roles fulfilled by PTEN has recently been expanded to include crucial functions in the nucleus, where it favors genomic stability and restrains cell cycle progression, as well as protein phosphatase dependent activity at the endoplasmic reticulum (ER) and mitochondria-associated membranes (MAMs), where PTEN interacts with the inositol 1,4,5-trisphosphate receptors (IP3Rs) and regulates Ca²⁺ release from the ER and sensitivity to apoptosis. Indeed, PTEN is present in definite subcellular locations where it performs distinct functions acting on specific effectors. In this review, we summarize recent advantages in methods to study PTEN subcellular localization and the distinct biological functions of PTEN in different cellular compartments. A deeper understanding of PTEN’s compartmentalized-functions will guide the rational design of novel therapies.