PTEN secretion in exosomes

Current Knowledge on Exosome Biogenesis, Cargo-Sorting Mechanism and Therapeutic Implications

Extracellular vesicles (EVs) are nanoscale membrane vesicles released by donor cells that can be taken up by recipient cells. The study of EVs has the potential to identify unknown cellular and molecular mechanisms in intercellular communication and disease. Exosomes, with an average diameter of ≈100 nanometers, are a subset of EVs. Different molecular families have been shown to be involved in the formation of exosomes and subsequent secretion of exosomes, which largely leads to the complexity of the form, structure and function of exosomes. In addition, because of their low immunogenicity and ability to transfer a variety of bioactive components to recipient cells, exosomes are regarded as effective drug delivery systems. This review summarizes the known mechanisms of exosomes biogenesis, cargo loading, exosomes release and bioengineering, which is of great importance for further exploration into the clinical applications of EVs.

Hypoxic Microenvironment-Induced Reduction in PTEN-L Secretion Promotes Non-Small Cell Lung Cancer Metastasis through PI3K/AKT Pathway

Objective

Lung cancer is the leading cause of cancer-related deaths worldwide. The aim of this study was to investigate the effects of hypoxic microenvironment on PTEN-L secretion and the effects of PTEN-L on the metastasis of non-small cell lung cancer (NSCLC) and the potential mechanisms.

Methods

The expression levels of PTEN-L in NSCLC tissues, cells, and cell culture media were detected. The transfection of PTEN-L overexpression construct or HIF-1α-siRNAs was conducted to manipulate the expression of PTEN-L or HIF-1α. NSCLC cells were introduced into 200 μM CoCl2 medium for 72 hours under 37°C to simulate hypoxia. The proliferation and apoptosis of the A549 cells were determined by the Cell Counting Kit-8 assay and Annexin V-FITC/PI-stained flow cytometry assay, respectively. Wound healing assay and transwell invasion assay were used to measure the migration and invasion of A549 cells. The protein expression of PTEN, PTEN-L, PI3K/AKT pathway-related proteins, and HIF-1α was detected by Western blot.

Results

PTEN and PTEN-L are downregulated in lung cancer tissues and cells. The protein expression of PTEN-L in the culture medium of lung cancer cell lines is decreased. The hypoxic microenvironment inhibits PTEN-L secretion. The low level of PTEN-L promotes cell proliferation, migration, and invasion, as well as inhibits apoptosis of A549 cells. The overexpression of PTEN-L attenuated the activation of the PI3K/AKT pathway by the hypoxic microenvironment. The knockdown of HIF-1α upregulates PTEN-L secretion under hypoxia.

Conclusions

The hypoxic microenvironment inhibits PTEN-L secretion and thus activates PI3K/AKT pathway to induce proliferation, migration, and invasion promotion, and apoptosis inhibition in NSCLC cells.

Inhibiting collagen I production and tumor cell colonization in the lung via miR-29a-3p loading of exosome-/liposome-based nanovesicles

The lung is one of the most common sites for cancer metastasis. Collagens in the lung provide a permissive microenvironment that supports the colonization and outgrowth of disseminated tumor cells. Therefore, down-regulating the production of collagens may contribute to the inhibition of lung metastasis. It has been suggested that miR-29 exhibits effective anti-fibrotic activity by negatively regulating the expression of collagens. Indeed, our clinical lung tumor data shows that miR-29a-3p expression negatively correlates with collagen I expression in lung tumors and positively correlates with patients’ outcomes. However, suitable carriers need to be selected to deliver this therapeutic miRNA to the lungs. In this study, we found that the chemotherapy drug cisplatin facilitated miR-29a-3p accumulation in the exosomes of lung tumor cells, and this type of exosomes exhibited a specific lung-targeting effect and promising collagen down-regulation. To scale up the preparation and simplify the delivery system, we designed a lung-targeting liposomal nanovesicle (by adjusting the molar ratio of DOTAP/cholesterol–miRNAs to 4:1) to carry miR-29a-3p and mimic the exosomes. This liposomal nanovesicle delivery system significantly down-regulated collagen I secretion by lung fibroblasts in vivo, thus alleviating the establishment of a pro-metastatic environment for circulating lung tumor cells.

Dynamic contrast-enhanced MRI predicts PTEN protein expression which can function as a prognostic measure of progression-free survival in NPC patients

OBJECTIVES

The objective of our study was to investigate whether a phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression was associated with dynamic contrast-enhanced MRI (DCE-MRI) parameters and prognosis in nasopharyngeal carcinoma (NPC).

METHODS

Two-hundred-and-forty-five (245) patients with NPC who underwent pretreatment biopsy, expression of PTEN detected by immunohistochemistry of biopsy, and radical intensity-modulated radiation therapy (IMRT) with or without chemotherapy were included. Tumor segmentations were delineated on pretreatment MRI manually. The pharmacokinetic parameters (K^trans, K_ep, V_e, and V_p) derived from dynamic contrast-enhanced MRI (DCE-MRI) using the extended Toft's model within the tumor segmentations were estimated. The following demographics and clinical features were assessed and correlated against each other: gender, age, TNM stage, clinical-stage, Epstein-Barr virus (EBV), pathological type, progression-free survival (PFS), and prognosis status. DCE parameter evaluation and clinical feature comparison between the PTEN positive and negative groups were performed and correlation between PTEN expression with the PFS and prognosis status using Cox regression for survival analysis were assessed.

RESULTS

A significantly lower K^trans and K_ep were found in NPC tumors in PTEN negative patients than in PTEN positive patients. K^trans performed better than K_ep in detecting PTEN expression with the ROC AUC of 0.752. PTEN negative was associated with later TNM stage, later clinical-stage, shorter PFS, and worse prognosis. Moreover, N stage, pathological type, K_ep, and prognostic status can be considered as independent variables in discrimination of PTEN negative expression in NPCs.

CONCLUSIONS

PTEN negative indicated a shorter PFS and worse prognosis than PTEN positive in NPC patients. K^trans and K_ep derived from DCE-MRI, which yielded reliable capability, may be considered as potential imaging markers that are correlated with PTEN expression and could be used to predict PTEN expression noninvasively. Combined radiological and clinical features can improve the performance of the classification of PTEN expression.

Tumour-derived exosomal miR-3473b promotes lung tumour cell intrapulmonary colonization by activating the nuclear factor-κB of local fibroblasts

Tumour‐derived exosomes have been shown to induce pre‐metastatic niche formation, favoring metastatic colonization of tumour cells, but the underlying molecular mechanism is still not fully understood. In this study, we showed that exosomes derived from the LLC cells could indeed significantly enhance their intrapulmonary colonization. Circulating LLC‐derived exosomes were mainly engulfed by lung fibroblasts and led to the NF‐κB signalling activation. Further studies indicated that the exosomal miR‐3473b was responsible for that by hindering the NFKB inhibitor delta's (NFKBID) function. Blocking miR‐3473b could reverse the exosome‐mediated NF‐κB activation of fibroblasts and decrease intrapulmonary colonization of lung tumour cells. Together, this study demonstrated that the miR‐3473b in exosomes could mediate the interaction of lung tumour cells and local fibroblasts in metastatic sites and, therefore, enhance the metastasis of lung tumour cells.

Redox regulation of tumor suppressor PTEN in cell signaling

Phosphatase and tensin homologs deleted on chromosome 10 (PTEN) is a potent tumor suppressor and often dysregulated in cancers. Cellular PTEN activity is restrained by the oxidation of active-site cysteine by reactive oxygen species (ROS). Recovery of its enzymatic activity predominantly depends on the availability of cellular thioredoxin (Trx) and peroxiredoxins (Prx), both are important players in cell signaling. Trx and Prx undergo redox-dependent conformational changes through the oxidation of cysteine residues at their active sites. Their dynamics are essential for protein functionality and regulation. In this review, we summarized the recent advances regarding the redox regulation of PTEN, with a specific focus on our current state-of-the-art understanding of the redox regulation of PTEN. We also proposed a tight association of the redox regulation of PTEN with Trx dimerization and Prx hyperoxidation, providing guidance for the identification of novel therapeutic targets.

Exosomal hsa-miR-21-5p derived from growth hormone-secreting pituitary adenoma promotes abnormal bone formation in acromegaly

Growth hormone-secreting pituitary adenoma (GHPA), a benign endocrine tumor located in the base of the skull, results in acromegaly. In addition to the mass effect of the tumor itself in the sellar region, GHPA can lead to the overgrowth of almost every organ. Previous findings indicated that the processes underlying acromegaly were partly attributable to hyperactivity of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis. However, the mechanisms driving this syndrome remains largely unknown. Additionally, the roles of GHPA-derived exosomes, which contain functional microRNAs and proteins that manipulate target cell proliferation and differentiation in distal extremities, are also unknown. In this study, we demonstrated that GHPA exosomes promote bone formation in vitro and trabecula number in vivo. The mechanism of increased trabecula formation may be attributable to GHPA exosome-induced osteoblast proliferation via increased cell viability and DNA replication. We further discovered that exosomal hsa-miR-21-5p plays a distinct role from the GH/IGF-1 axis in these processes. Accordingly, the results of this study provide a novel mechanism whereby GHPA influences distal extremities and a new perspective for treating GHPA.

Overexpression of MALAT1 Relates to Lung Injury through Sponging miR-425 and Promoting Cell Apoptosis during ARDS

Background

Acute respiratory distress syndrome (ARDS) is a severe form of acute lung injury during which severe inflammatory responses induce cell apoptosis, necrosis, and fibrosis. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a multiple function long noncoding RNA that was found overexpressed during acute lung injury. However, the roles of MALAT1 in ARDS patients are still unknown.

Methods

Total RNA was extracted from the plasma, plasma exosome, and peripheral blood mononuclear cells (PBMCs) from 65 ARDS patients and 36 healthy controls. The MALAT1 and six candidate miRNAs levels were detected by qRT-PCR. The interaction between MALAT1 and miR-425 was predicted using a bioinformatics tool and verified by dual luciferase assay. Exosomes from ARDS patients were cultured with A549 and HFL-1 cells to confirm the delivery of miR-425 by exosomes. Cell apoptosis and viability were determined by flow cytometry and MTT assay.

Results

We found MALAT1 was significantly increased in the ARDS patients' plasma and PBMCs. The MALAT1 level in PBMCs was negatively correlated with exosomal miR-425 level. MALAT1 interacted with miR-425 and protected phosphatase and tensin homolog (PTEN) expression in A549 and HFL-1 cells. Exosomes from ARDS patients delivered less miR-425 into A549 and HFL-1 cells and induced cell apoptosis via upregulating PTEN.

Conclusion

This study identified increased MALAT1 and decreased miR-425 in ARDS patients and unveiled their roles during the pathogenesis of ARDS.

Programming of macrophages by UV-irradiated apoptotic cancer cells inhibits cancer progression and lung metastasis

Apoptotic cell clearance by phagocytes is essential in tissue homeostasis. We demonstrated that conditioned medium (CM) from macrophages exposed to apoptotic cancer cells inhibits the TGFβ1-induced epithelial–mesenchymal transition (EMT), migration, and invasion of cancer cells. Apoptotic 344SQ (ApoSQ) cell-induced PPARγ activity in macrophages increased the levels of PTEN, which was secreted in exosomes. Exosomal PTEN was taken up by recipient lung cancer cells. ApoSQ-exposed CM from PTEN knockdown cells failed to enhance PTEN in 344SQ cells, restore cellular polarity, or exert anti-EMT and anti-invasive effects. The CM that was deficient in PPARγ ligands, including 15-HETE, lipoxin A4, and 15d-PGJ₂, could not reverse the suppression of PPARγ activity or the PTEN increase in 344SQ cells and consequently failed to prevent the EMT process. Moreover, a single injection of ApoSQ cells inhibited lung metastasis in syngeneic immunocompetent mice with enhanced PPARγ/PTEN signaling both in tumor-associated macrophages and in tumor cells. PPARγ antagonist GW9662 reversed the signaling by PPARγ/PTEN; the reduction in EMT-activating transcription factors, such as Snai1 and Zeb1; and the antimetastatic effect of the ApoSQ injection. Thus, the injection of apoptotic lung cancer cells may offer a new strategy for the prevention of lung metastasis.

A chimeric protein PTEN-L-p53 enters U251 cells to repress proliferation and invasion

PTEN, a well-known tumor suppressor, dephosphorylates PIP3 and inhibits AKT activity. A translational variant of PTEN has been identified and termed PTEN-Long (PTEN-L). The additional 173 amino acids (PTEN-L leader) at the N-terminal constitute a potential signal peptide. Differing from canonical PTEN, PTEN-L is secreted into the extracellular fluid and re-enters recipient cells, playing the similar roles as PTEN in vivo and in vitro. This character confers the PTEN-L a therapeutic ability via directly protein delivering instead of traditional DNA and RNA vector options. In the present study, we employed PTEN-L leader to assemble a fusion protein, PTEN-L-p53, inosculated with the transcriptional regulator TP53, which is another powerful tumor suppressor. We overexpressed PTEN-L-p53 in HEK293T cells and detected it in both the cytoplasm and nucleus. Subsequently, we found that PTEN-L-p53 was secreted outside of the cells and detected in the culture media by immunoblotting. Furthermore, we demonstrated that PTEN-L-p53 freely entered the cells and suppressed the viability of U251cells (p53^R273H, a cell line with p53 R273H-mutation). PTEN-L-p53 is composed of endogenous protein/peptide bearing low immunogenicity, and only the junction region between PTEN-L leader and p53 can act as a new immune epitope. Accordingly, this fusion protein can potentially be used as a therapeutic option for TP53-abnormality cancers.

PTEN is a protein phosphatase that targets active PTK6 and inhibits PTK6 oncogenic signaling in prostate cancer

PTEN activity is often lost in prostate cancer. We show that the tyrosine kinase PTK6 (BRK) is a PTEN substrate. Phosphorylation of PTK6 tyrosine 342 (PY342) promotes activation, while phosphorylation of tyrosine 447 (PY447) regulates auto-inhibition. Introduction of PTEN into a PTEN null prostate cancer cell line leads to dephosphorylation of PY342 but not PY447 and PTK6 inhibition. Conversely, PTEN knockdown promotes PTK6 activation in PTEN positive cells. Using a variety of PTEN mutant constructs, we show that protein phosphatase activity of PTEN targets PTK6, with efficiency similar to PTP1B, a phosphatase that directly dephosphorylates PTK6 Y342. Conditional disruption of Pten in the mouse prostate leads to tumorigenesis and increased phosphorylation of PTK6 Y342, and disruption of Ptk6 impairs tumorigenesis. In human prostate tumor tissue microarrays, loss of PTEN correlates with increased PTK6 PY342 and poor outcome. These data suggest PTK6 activation promotes invasive prostate cancer induced by PTEN loss.

PTEN is often lost in prostate cancer. In this study, the authors show that PTEN can act as a protein phosphatase that targets active PTK6, thereby regulating its oncogenic signaling in prostate cancer progression.

PTEN-L promotes type I interferon responses and antiviral immunity

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a well-known tumor suppressor that acts as a dual-specificity phosphatase and is frequently mutated in human cancer. Our previous work has demonstrated that PTEN also plays a vital role in type I interferon responses and antiviral innate immunity. Recently, a translational variant of PTEN with a long N-terminal extension (PTEN-L) has been discovered that is secreted into the extracellular environment and enters recipient cells, where it exerts a phosphatase function antagonistic to PI3K/Akt signaling and tumorigenesis. In this study, we demonstrate that PTEN-L promotes type I interferon responses and antiviral innate immunity during viral infection in a phosphatase activity-dependent manner. Compared with canonical PTEN, PTEN-L also exerts its antiviral function when it is applied exogenously in protein form. This finding was confirmed in cell cultures and mouse infection models. Furthermore, PTEN-L enhances the responses of both type I interferon and proinflammatory cytokines, thus suggesting that PTEN-L might possess additional functions compared with those of PTEN. Thus, the antiviral function of PTEN-L may open an avenue for the use of PTEN-L in antiviral therapy, particularly in patients with PTEN-deficient tumors.

Engineering Recombinant Protein Sensors for Quantifying Histone Acetylation

H3K14ac (acetylation of lysine 14 of histone H3) is one of the most important epigentic modifications. Aberrant changes in H3K14ac have been associated with various diseases, including cancers and neurological disorders. Tools that enable detection and quantification of H3K14ac levels in cell extracts and in situ are thus of critical importance to reveal its role in various biological processes. Current detection techniques of specific histone modifications, however, are constrained by tedious sample pretreatments, lack of quantitative accuracy, and reliance on high quality antibodies. To address this issue, we engineered recombinant sensors that are suitable for probing histone acetylation levels using various biological samples. The protein sensor contains recongition domain(s) with sequences derived from the bromodomain of human polybromo-1 (PB1), a natural H3K14ac reader domain. Various sensor designs were tested using nuclear extracts and live cells. The sensor containing dimeric repeats of bromodomain was found most effective in quantifying H3K14ac level in both in vitro and in situ assays. The sensor has a linear detection range of 0.5-50 nM when mixed with nuclear extracts. The sensor colocalizes with H3K14ac antibodies in situ when transfected into human embryonic kidney 293T (HEK293T) cells and is thus capable of providing spatial details of histone modification within the nucleus. Corrected nuclear fluorescence intensity was used to quantify the modification level in situ and found to correlate well with our in vitro assays. Our sensor offers a novel tool to characterize the histone modification level using nuclear extracts and probe histone modification change in live cells.

The potential of tumor-derived exosomes for noninvasive cancer monitoring

Tumor-derived exosomes (TEX) are emerging as a new type of cancer biomarker. TEX are membrane-bound, virus-size vesicles of endocytic origin present in all body fluids of cancer patients. Based on the expanding albeit incomplete knowledge of their biogenesis, secretion by tumor cells and cancer cell-specific molecular and genetic contents, TEX are viewed as promising, clinically-relevant surrogates of cancer progression and response to therapy. Preliminary proteomic, genetic and functional profiling of tumor cell-derived or cancer plasma-derived exosomes confirms their unique characteristics. Alterations in protein or nucleic acid profiles of exosomes in plasma of cancer patients responding to therapies appear to correlate with clinical endpoints. However, methods for TEX isolation and separation from the bulk of human plasma-derived exosomes are not yet established and their role as biomarkers remains to be confirmed. Further development and validation of TEX as noninvasive, liquid equivalents of tumor biopsies are necessary to move this effort forward.