Crystal Structure and Substrate Specificity of PTPN12

The impact of nitric oxide on HER family post-translational modification and downstream signaling in cancer

The human epidermal growth factor receptor (HER) family consists of four members, activated by two families of ligands. They are known for mediating cell-cell interactions in organogenesis, and their deregulation has been associated with various cancers, including breast and esophageal cancers. In particular, aberrant epidermal growth factor receptor (EGFR) and HER2 signaling drive disease progression and result in poorer patient outcomes. Nitric oxide (NO) has been proposed as an alternative activator of the HER family and may play a role in this aberrant activation due to its ability to induce s-nitrosation and phosphorylation of the EGFR. This review discusses the potential impact of NO on HER family activation and downstream signaling, along with its role in the efficacy of therapeutics targeting the family.

PTPN12 down-regulated by miR-146b-3p gene affects the malignant progression of laryngeal squamous cell carcinoma

Laryngeal squamous cell carcinoma (LSCC) is a common malignancy among men in the anatomical position of head and neck. Hoarseness, pharyngalgia, and dyspnea are common symptoms. LSCC is a complex polygenic carcinoma that is caused by many factors involving polygenic alteration, environmental pollution, tobacco, and human papillomavirus. Classical protein tyrosine phosphatase nonreceptor type 12 (PTPN12) has been extensively studied to decipher its mechanism as a tumor suppressor gene in various human carcinomas; however, there is no comprehensive elucidation of the PTPN12 expression and its regulatory mechanisms in LSCC. As such, we expect to provide new insights for finding new biomarkers and effective therapeutic targets in LSCC. Immunohistochemical staining, western blot (WB), and quantitative real-time RT-PCR (qRT-PCR) were used for the messenger RNA (mRNA) and protein expression analyses of PTPN12, respectively. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, clone formation, transwell migration, and transwell invasion assays were used to assess the proliferation, migration, and invasion ability of LSCC cells. Online prediction and design software tools (http://www.targetscan.org/ and http://www.microRNA.org) were used to predict associated miRNA. Studying the targeted regulatory relationship between miR-146b-3p and PTPN12 was based on dual luciferase reporter gene analysis. qRT-PCR was used to assess miR-146b-3p expression in LSCC. miR-146b-3p inhibitor and mimic were transfected, followed by qRT-PCR and WB assays to detect the expression of PTPN12. The gain and loss functional experiments were used to investigate the effects of miR-146b-3p transfection on the proliferation, migration, and invasion of tumor cells. Online bioinformatics prediction software (https://cn.string-db.org/ and https://www.genecards.org/) was used to determine potential downstream target genes of PTPN12. qRT-PCR and WB analyses were used to assess the mRNA and protein expression levels of target genes. Our study showed significantly decreased mRNA and protein expression levels of PTPN12 in LSCC compared with the adjacent normal tissues. The lower PTPN12 mRNA expression was correlated with pathological differentiation, and lower PTPN12 protein expression was correlated with the TNM stage in LSCC tissues. The subsequent in vitro functional analyses showed the inhibitory effect of PTPN12 over-expression on the proliferation, migration, and invasiveness abilities of LSCC cell line. Using online prediction and design software, miR-146b-3p was searched to target PTPN12. The miR-146b-3p was expressed at a high level in LSCC tissues and cell lines. Luciferase reporter assay exhibited that miR-146b-3p inhibited the luciferase activity of PTPN12 markedly. The functional analyses showed the tumor-promoting role of miR-146b-3p on the proliferation, migration, and invasiveness abilities of LSCC cell. Furthermore, co-transfection of cells with miR-146b-3p and PTPN12 significantly restored the inhibitory effect of PTPN12 on LSCC cell growth, migration, and invasiveness. This phenomenon unveiled that miR-146b-3p regulated the proliferation, migration, and invasion of LSCC cells by targeting PTPN12. EGFR and ERBB2 were selected as the downstream-regulation target genes. Up-regulation of PTPN12 significantly suppressed EGFR expression. Accordingly, the miR-146b-3p mimic significantly up-regulated the EGFR expression. However, up-regulation of PTPN12 and miR-146b-3p mimic suppressed ERBB2 protein expression but induced its gene expression. Down-regulation of PTPN12 is associated with up-regulation of miR-146b-3p in LSCC. Moreover, PTPN12 serves as a tumor suppressor gene through regulating the proliferation, migration, and invasion of LSCC cells. miR-146b-3p/PTPN12 axis is expected to be a novel therapeutic target in LSCC.

Protein tyrosine phosphatase non-receptor type 12 suppresses tumor progression in osteosarcoma cells

BACKGROUND

Protein tyrosine phosphatase non-receptor 12 (PTPN12) plays a prominent role in various cancers as a tumor suppressor. However, the expression of PTPN12 and its biological functions in osteosarcoma (OS) remains to be determined.

METHODS

PTPN12 expression in OS was explored in public databases and detected by immunohistochemistry and Western blot. The cell viability was determined by Cell Counting Kit-8 (CCK-8) assay and colony formation. The cell migration and invasion were assessed by the Transwell assay. Flow cytometry analysis was applied to detect cell apoptosis and cell cycle distribution. To investigate the related mechanism, the levels of EGFR and downstream proteins were detected by Western blot.

RESULTS

PTPN12 expression was significantly decreased in OS samples in GEO database and our hospital. OS cell lines in Cancer Cell Line Encyclopedia (CCLE) database and our cultured OS cells also demonstrated low PTPN12 expression. Lentivirus-induced overexpression of PTPN12 significantly inhibited the cell viability, migration and invasion of 143B and U2OS cells. The results of flow cytometry found that PTPN12 overexpression promoted cell apoptosis and induced cell cycle arrest at G1 phase in 143B and U2OS cells. The phosphorylation levels of EGFR and subsequent proteins of the PI3K/AKT and ERK pathways were inactivated as a result of PTPN12 overexpression in OS.

CONCLUSION

PTPN12 plays a tumor suppressive role in OS cells. Restoring of PTPN12 activity may provide new insights for the treatment of this disease.

GABAB1e promotes the malignancy of human cancer cells by targeting the tyrosine phosphatase PTPN12

Neurotransmitter receptors are involved in cancer progression. Among them, the heterodimeric GABA_B receptor, activated by the main inhibitory neurotransmitter GABA, is composed of the transmembrane GABA_B1 and GABA_B2 subunits. The oncogenic role of the isoform GABA_B1e (GB_1e) containing only the extracellular domain of GABA_B1 remains unclear. We revealed that GB_1e is largely expressed in human breast cancer (BrCa) cell lines as well as in BrCa tissues where it is upregulated. Moreover, GB_1e promoted the malignancy of BrCa cells both in vitro and in vivo. We propose that GB_1e favors EGFR signaling by interacting with PTPN12 to disrupt the interaction between EGFR and PTPN12, and phosphorylation of Y230 and Y404 on GB_1e is required in this process. Our data highlight that the GABBR1 gene through the expression of the GB_1e isoform might play an important oncogenic role in BrCa and that GB_1e is of interest for the treatment of some cancers.

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GABA_B1e promotes the malignancy of breast cancer cells both in vitro and in vivo

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Specific phosphorylation of GABA_B1e is critical for its association with PTPN12

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GABA_B1e disrupts EGFR interacting with PTPN12 and induces EGFR-PI3K/Akt signaling

Microbially Guided Discovery and Biosynthesis of Biologically Active Natural Products

The design of small molecules that inhibit disease-relevant proteins represents a longstanding challenge of medicinal chemistry. Here, we describe an approach for encoding this challenge-the inhibition of a human drug target-into a microbial host and using it to guide the discovery and biosynthesis of targeted, biologically active natural products. This approach identified two previously unknown terpenoid inhibitors of protein tyrosine phosphatase 1B (PTP1B), an elusive therapeutic target for the treatment of diabetes and cancer. Both inhibitors appear to target an allosteric site, which confers selectivity, and can inhibit PTP1B in living cells. A screen of 24 uncharacterized terpene synthases from a pool of 4464 genes uncovered additional hits, demonstrating a scalable discovery approach, and the incorporation of different PTPs into the microbial host yielded alternative PTP-specific detection systems. Findings illustrate the potential for using microbes to discover and build natural products that exhibit precisely defined biochemical activities yet possess unanticipated structures and/or binding sites.

Spatially interacting phosphorylation sites and mutations in cancer

Advances in mass-spectrometry have generated increasingly large-scale proteomics datasets containing tens of thousands of phosphorylation sites (phosphosites) that require prioritization. We develop a bioinformatics tool called HotPho and systematically discover 3D co-clustering of phosphosites and cancer mutations on protein structures. HotPho identifies 474 such hybrid clusters containing 1255 co-clustering phosphosites, including RET p.S904/Y928, the conserved HRAS/KRAS p.Y96, and IDH1 p.Y139/IDH2 p.Y179 that are adjacent to recurrent mutations on protein structures not found by linear proximity approaches. Hybrid clusters, enriched in histone and kinase domains, frequently include expression-associated mutations experimentally shown as activating and conferring genetic dependency. Approximately 300 co-clustering phosphosites are verified in patient samples of 5 cancer types or previously implicated in cancer, including CTNNB1 p.S29/Y30, EGFR p.S720, MAPK1 p.S142, and PTPN12 p.S275. In summary, systematic 3D clustering analysis highlights nearly 3,000 likely functional mutations and over 1000 cancer phosphosites for downstream investigation and evaluation of potential clinical relevance.

PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates

Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY⁸³ site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY¹²⁵ and MUNC18-1-pY¹⁴⁵ sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY¹⁴⁵ or DYNAMIN2-pY¹²⁵ through a distinct structural basis compared with that of the NSF-pY⁸³ site. Our studies thus provide mechanistic insights in complex exocytosis processes.

Molecular dynamics simulation studies on the specific regulation of PTPN18 to the HER2 phospho-peptides

The specific regulation of PTPN18 protein to three HER2 phospho-peptides has been studied by molecular dynamics simulations and free energy calculations. The results revealed that the three HER2 phospho-peptides binding to the PTPN18 catalytic domain is energetically favorable due to substrate specificity of PTPN18, and moreover, the PTPN18 protein have significantly higher affinity to pY1248 peptide (-45.22 kcal/mol) than that of pY1112 (-25.3 kcal/mol) and pY1196 (-31.86 kcal/mol) peptides. Further, the binding of HER2 phospho-peptides to PTPN18 have also caused the closure of WPD-loop with the decrease of the centroid distances between the P-loop and the WPD loop. The WPD-loop closure of PTPN18 relates directly to the new hydrogen bond and hydrophobic interaction formations between the residues Tyr62, Asp64, Val65, Ala231, Arg235, and Ala273 in PTPN18 and Tyr(PO3) in the HER2 phospho-peptides, which suggests that these key residues would contribute to the specific regulation of PTPN18 to the substrates. The correlation analysis revealed the allosteric communication networks from the pY binding loop to the WPD loop through the structural change and the residue interactions in PTPN18. These results will be helpful to understand the specific regulation through the allosteric communication network in the PTPN18 catalytic domain.

The protein tyrosine phosphatase PTP-PEST mediates hypoxia-induced endothelial autophagy and angiogenesis via AMPK activation

Global and endothelial loss of PTP-PEST (also known as PTPN12) is associated with impaired cardiovascular development and embryonic lethality. Although hypoxia is implicated in vascular remodelling and angiogenesis, its effect on PTP-PEST remains unexplored. Here we report that hypoxia (1% oxygen) increases protein levels and catalytic activity of PTP-PEST in primary endothelial cells. Immunoprecipitation followed by mass spectrometry revealed that α subunits of AMPK (α1 and α2, encoded by PRKAA1 and PRKAA2, respectively) interact with PTP-PEST under normoxia but not in hypoxia. Co-immunoprecipitation experiments confirmed this observation and determined that AMPK α subunits interact with the catalytic domain of PTP-PEST. Knockdown of PTP-PEST abrogated hypoxia-mediated tyrosine dephosphorylation and activation of AMPK (Thr172 phosphorylation). Absence of PTP-PEST also blocked hypoxia-induced autophagy (LC3 degradation and puncta formation), which was rescued by the AMPK activator metformin (500 µM). Because endothelial autophagy is a prerequisite for angiogenesis, knockdown of PTP-PEST also attenuated endothelial cell migration and capillary tube formation, with autophagy inducer rapamycin (200 nM) rescuing angiogenesis. In conclusion, this work identifies for the first time that PTP-PEST is a regulator of hypoxia-induced AMPK activation and endothelial autophagy to promote angiogenesis.

Progress in the correlation between PTPN12 gene expression and human tumors

BACKGROUND

The global morbidity of cancer is rising rapidly. Despite advances in molecular biology, immunology, and cytotoxic and immune-anticancer therapies, cancer remains a major cause of death worldwide. Protein tyrosine phosphatase non-receptor type 12 (PTPN12) is a new member of the cytoplasmic protein tyrosine phosphatase family, isolated from a cDNA library of adult colon tissue. Thus far, no studies have reviewed the correlation between PTPN12 gene expression and human tumors.

METHODS

This article summarizes the latest domestic and international research developments on how the expression of PTPN12 relates to human tumors. The extensive search in Web of Science and PubMed with the keywords including PTPN12, tumor, renal cell carcinoma, proto-oncogenes, tumor suppressor genes was undertaken.

RESULTS

More and more studies have shown that a tumor is essentially a genetic disease, arising from a broken antagonistic function between proto-oncogenes and tumor suppressor genes. When their antagonistic effect is out of balance, it may cause uncontrolled growth of cells and lead to the occurrence of tumors. PTPN12 is a tumor suppressor gene, so inhibiting its activity will lead directly or indirectly to the occurrence of tumors.

CONCLUSION

The etiology, prevention, and treatment of tumors have become the focus of research around the world. PTPN12 is a tumor suppressor gene. In the future, PTPN12 might serve as a novel molecular marker to benefit patients, and even the development of tumor suppressor gene activation agents can form a practical research direction.

Inhibition of striatal-enriched protein tyrosine phosphatase by targeting computationally revealed cryptic pockets

Cryptic pockets, which are not apparent in crystallographic structures, provide promising alternatives to traditional binding sites for drug development. However, identifying cryptic pockets is extremely challenging and the therapeutic potential of cryptic pockets remains unclear. Here, we reported the discovery of novel inhibitors for striatal-enriched protein tyrosine phosphatase (STEP), a potential drug target for multiple neuropsychiatric disorders, based on cryptic pocket detection. By combining the use of molecular dynamics simulations and fragment-centric topographical mapping, we identified transiently open cryptic pockets and identified 12 new STEP inhibition scaffolds through structure-based virtual screening. Site-directed mutagenesis verified the binding of ST3 with the predicted cryptic pockets. Moreover, the most potent and selective inhibitors could modulate the phosphorylation of both ERK1/2 and Pyk2 in PC12 cells.

High-level expression of protein tyrosine phosphatase non-receptor 12 is a strong and independent predictor of poor prognosis in prostate cancer

BACKGROUND

Protein tyrosine phosphatase non-receptor 12 (PTPN12) is ubiquitously tyrosine phosphatase with tumor suppressive properties.

METHODS

PTPN12 expression was analyzed by immunohistochemistry on a tissue microarray with 13,660 clinical prostate cancer specimens.

RESULTS

PTPN12 staining was typically absent or weak in normal prostatic epithelium but seen in the majority of cancers, where staining was considered weak in 26.5%, moderate in 39.9%, and strong in 4.7%. High PTPN12 staining was associated with high pT category, high classical and quantitative Gleason grade, lymph node metastasis, positive surgical margin, high Ki67 labeling index and early prostate specific antigen recurrence (p < 0.0001 each). PTPN12 staining was seen in 86.4% of TMPRSS2:ERG fusion positive but in only 58.4% of ERG negative cancers. Subset analyses discovered that all associations with unfavorable phenotype and prognosis were markedly stronger in ERG positive than in ERG negative cancers but still retained in the latter group. Multivariate analyses revealed an independent prognostic impact of high PTPN12 expression in all cancers and in the ERG negative subgroup and to a lesser extent also in ERG positive cancers. Comparison with 12 previously analyzed chromosomal deletions revealed that high PTPN12 expression was significantly associated with 10 of 12 deletions in ERG negative and with 7 of 12 deletions in ERG positive cancers (p < 0.05 each) indicating that PTPN12 overexpression parallels increased genomic instability in prostate cancer.

CONCLUSIONS

These data identify PTPN12 as an independent prognostic marker in prostate cancer. PTPN12 analysis, either alone or in combination with other biomarkers might be of clinical utility in assessing prostate cancer aggressiveness.

Chemical proteomics reveals new targets of cysteine sulfinic acid reductase

Cysteine sulfinic acid or S-sulfinylation is an oxidative post-translational modification (OxiPTM) that is known to be involved in redox-dependent regulation of protein function but has been historically difficult to analyze biochemically. To facilitate the detection of S-sulfinylated proteins, we demonstrate that a clickable, electrophilic diazene probe (DiaAlk) enables capture and site-centric proteomic analysis of this OxiPTM. Using this workflow, we revealed a striking difference between sulfenic acid modification (S-sulfenylation) and the S-sulfinylation dynamic response to oxidative stress, which is indicative of different roles for these OxiPTMs in redox regulation. We also identified >55 heretofore-unknown protein substrates of the cysteine sulfinic acid reductase sulfiredoxin, extending its function well beyond those of 2-cysteine peroxiredoxins (2-Cys PRDX1-4) and offering new insights into the role of this unique oxidoreductase as a central mediator of reactive oxygen species-associated diseases, particularly cancer. DiaAlk therefore provides a novel tool to profile S-sulfinylated proteins and study their regulatory mechanisms in cells.

Proteomic Identification of Protein Tyrosine Phosphatase and Substrate Interactions in Living Mammalian Cells by Genetic Encoding of Irreversible Enzyme Inhibitors

Protein tyrosine phosphatases (PTPs) play critical roles in cell signaling pathways, but identification of unknown PTPs for a given substrate in live cells remain technically challenging. Here, we synthesized a series of tyrosine-based irreversible PTP inhibitors and characterized by site-specific encoding on substrate proteins in cells with an expanded genetic code. By fine-tuning the chemical reactivity, we identified optimal active amino acid probes to covalently cross-link a PTP and its substrate both in vitro and in mammalian cells. Using HER2 as an example, we provide first direct evidence of HER2 Y1023 and SHP2 cross-linking in situ in living human cells. Moreover, proteomic analysis using our approach identified PTP1B as a novel phosphatase for HER2 that specifically dephosphorylated pY1221 position, which may shed light on the puzzle of PTP1B's role in HER2 positive breast cancer. This novel method provides a useful tool for dissecting tyrosine phosphoregulation in living cells.

Allosteric modulation of the catalytic VYD loop in Slingshot by its N-terminal domain underlies both Slingshot auto-inhibition and activation

Slingshots are phosphatases that modulate cytoskeleton dynamics, and their activities are tightly regulated in different physiological contexts. Recently, abnormally elevated Slingshot activity has been implicated in many human diseases, such as cancer, Alzheimer's disease, and vascular diseases. Therefore, Slingshot-specific inhibitors have therapeutic potential. However, an enzymological understanding of the catalytic mechanism of Slingshots and of their activation by actin is lacking. Here, we report that the N-terminal region of human Slingshot2 auto-inhibits its phosphatase activity in a noncompetitive manner. pH-dependent phosphatase assays and leaving-group dependence studies suggested that the N-terminal domain of Slingshot2 regulates the stability of the leaving group of the product during catalysis by modulating the general acid Asp³⁶¹ in the catalytic VYD loop. F-actin binding relieved this auto-inhibition and restored the function of the general acid. Limited tryptic digestion and biophysical studies identified large conformational changes in Slingshot2 after the F-actin binding. The dissociation of N-terminal structural elements, including Leu⁶³, and the exposure of the loop between α-helix-2 and β-sheet-3 of the phosphatase domain served as the structural basis for Slingshot activation via F-actin binding in vitro and via neuregulin stimulation in cells. Moreover, we designed a FlAsH-BRET-based Slingshot2 biosensor whose readout was highly correlated with the in vivo phosphatase activities of Slingshot2. Our results reveal the auto-inhibitory mechanism and allosteric activation mechanisms of a human Slingshot phosphatase. They also contribute to the design of new strategies to study Slingshot regulation in various cellular contexts and to screen for new activators/inhibitors of Slingshot activity.

Allosteric mechanisms underlie GPCR signaling to SH3-domain proteins through arrestin

Signals from 800 G-protein-coupled receptors (GPCRs) to many SH3 domain-containing proteins (SH3-CPs) regulate important physiological functions. These GPCRs may share a common pathway by signaling to SH3-CPs via agonist-dependent arrestin recruitment rather than through direct interactions. In the present study, ¹⁹F-NMR and cellular studies revealed that downstream of GPCR activation engagement of the receptor-phospho-tail with arrestin allosterically regulates the specific conformational states and functional outcomes of remote β-arrestin 1 proline regions (PRs). The observed NMR chemical shifts of arrestin PRs were consistent with the intrinsic efficacy and specificity of SH3 domain recruitment, which was controlled by defined propagation pathways. Moreover, in vitro reconstitution experiments and biophysical results showed that the receptor-arrestin complex promoted SRC kinase activity through an allosteric mechanism. Thus, allosteric regulation of the conformational states of β-arrestin 1 PRs by GPCRs and the allosteric activation of downstream effectors by arrestin are two important mechanisms underlying GPCR-to-SH3-CP signaling.

PTPN12/PTP-PEST Regulates Phosphorylation-Dependent Ubiquitination and Stability of Focal Adhesion Substrates in Invasive Glioblastoma Cells

Glioblastoma (GBM) is an invasive brain cancer with tumor cells that disperse from the primary mass, escaping surgical resection and invariably giving rise to lethal recurrent lesions. Here we report that PTP-PEST, a cytoplasmic protein tyrosine phosphatase, controls GBM cell invasion by physically bridging the focal adhesion protein Crk-associated substrate (Cas) to valosin-containing protein (Vcp), an ATP-dependent protein segregase that selectively extracts ubiquitinated proteins from multiprotein complexes and targets them for degradation via the ubiquitin proteasome system. Both Cas and Vcp are substrates for PTP-PEST, with the phosphorylation status of tyrosine 805 (Y805) in Vcp impacting affinity for Cas in focal adhesions and controlling ubiquitination levels and protein stability. Perturbing PTP-PEST-mediated phosphorylation of Cas and Vcp led to alterations in GBM cell-invasive growth in vitro and in preclinical mouse models. Collectively, these data reveal a novel regulatory mechanism involving PTP-PEST, Vcp, and Cas that dynamically balances phosphorylation-dependent ubiquitination of key focal proteins involved in GBM cell invasion.Significance: PTP-PEST balances GBM cell growth and invasion by interacting with the ATP-dependent ubiquitin segregase Vcp/p97 and regulating phosphorylation and stability of the focal adhesion protein p130Cas.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/14/3809/F1.large.jpg Cancer Res; 78(14); 3809-22. ©2018 AACR.

Combinatorial inhibition of PTPN12-regulated receptors leads to a broadly effective therapeutic strategy in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer diagnosed in more than 200,000 women each year and is recalcitrant to targeted therapies. Although TNBCs harbor multiple hyperactive receptor tyrosine kinases (RTKs), RTK inhibitors have been largely ineffective in TNBC patients thus far. We developed a broadly effective therapeutic strategy for TNBC that is based on combined inhibition of receptors that share the negative regulator PTPN12. Previously, we and others identified the tyrosine phosphatase PTPN12 as a tumor suppressor that is frequently inactivated in TNBC. PTPN12 restrains several RTKs, suggesting that PTPN12 deficiency leads to aberrant activation of multiple RTKs and a co-dependency on these receptors. This in turn leads to the therapeutic hypothesis that PTPN12-deficient TNBCs may be responsive to combined RTK inhibition. However, the repertoire of RTKs that are restrained by PTPN12 in human cells has not been systematically explored. By methodically identifying the suite of RTK substrates (MET, PDGFRβ, EGFR, and others) inhibited by PTPN12, we rationalized a combination RTK-inhibitor therapy that induced potent tumor regression across heterogeneous models of TNBC. Orthogonal approaches revealed that PTPN12 was recruited to and inhibited these receptors after ligand stimulation, thereby serving as a feedback mechanism to limit receptor signaling. Cancer-associated mutation of PTPN12 or reduced PTPN12 protein levels diminished this feedback mechanism, leading to aberrant activity of these receptors. Restoring PTPN12 protein levels restrained signaling from RTKs, including PDGFRβ and MET, and impaired TNBC survival. In contrast with single agents, combined inhibitors targeting the PDGFRβ and MET receptors induced the apoptosis in TNBC cells in vitro and in vivo. This therapeutic strategy resulted in tumor regressions in chemo-refractory patient-derived TNBC models. Notably, response correlated with PTPN12 deficiency, suggesting that impaired receptor feedback may establish a combined addiction to these proto-oncogenic receptors. Taken together, our data provide a rationale for combining RTK inhibitors in TNBC and other malignancies that lack receptor-activating mutations.

Proteomic Identification of Heat Shock-Induced Danger Signals in a Melanoma Cell Lysate Used in Dendritic Cell-Based Cancer Immunotherapy

Autologous dendritic cells (DCs) loaded with cancer cell-derived lysates have become a promising tool in cancer immunotherapy. During the last decade, we demonstrated that vaccination of advanced melanoma patients with autologous tumor antigen presenting cells (TAPCells) loaded with an allogeneic heat shock- (HS-) conditioned melanoma cell-derived lysate (called TRIMEL) is able to induce an antitumor immune response associated with a prolonged patient survival. TRIMEL provides not only a broad spectrum of potential melanoma-associated antigens but also danger signals that are crucial in the induction of a committed mature DC phenotype. However, potential changes induced by heat conditioning on the proteome of TRIMEL are still unknown. The identification of newly or differentially expressed proteins under defined stress conditions is relevant for understanding the lysate immunogenicity. Here, we characterized the proteomic profile of TRIMEL in response to HS treatment. A quantitative label-free proteome analysis of over 2800 proteins was performed, with 91 proteins that were found to be regulated by HS treatment: 18 proteins were overexpressed and 73 underexpressed. Additionally, 32 proteins were only identified in the HS-treated TRIMEL and 26 in non HS-conditioned samples. One protein from the overexpressed group and two proteins from the HS-exclusive group were previously described as potential damage-associated molecular patterns (DAMPs). Some of the HS-induced proteins, such as haptoglobin, could be also considered as DAMPs and candidates for further immunological analysis in the establishment of new putative danger signals with immunostimulatory functions.

PTPN12 Affects Nasopharyngeal Carcinoma Cell Proliferation and Migration Through Regulating EGFR

OBJECTIVE

Nasopharyngeal carcinoma (NPC) shows the leading morbidity in otorhinolaryngological malignant tumor. It is a common malignancy in China with obvious reginal distribution. NPC is a polygenic disease that is affected by numerous factors. Protein tyrosine phosphatase nonreceptor type 12 (PTPN12) regulates multiple tumor proliferation and development, including breast cancer and colon cancer. However, the role of PTPN12 in NPC occurrence and development has not been elucidated.

PATIENTS AND METHODS

NPC cell line CNE2 was cultured in vitro and divided into three groups, including control, empty plasmid, and PTPN12 groups. PTPN12 mRNA and protein expressions were tested by real-time polymerase chain reaction and Western blot. CNE2 cell proliferation was detected by MTT assay. Cell migration was determined by wound healing assay. Cell apoptosis was evaluated by caspase 3 activity detection. Epidermal growth factor receptor (EGFR) expression was assessed by Western blot.

RESULTS

PTPN12 plasmid transfection increased PTPN12 mRNA and protein expressions, suppressed cell proliferation and migration, reduced EGFR level, and enhanced caspase 3 activity compared with control and empty plasmid groups (p < 0.05).

CONCLUSIONS

PTPN12 regulates NPC proliferation and migration through negative regulating EGFR. It could be treated as a molecular target for NPC diagnosis and prognosis analysis.

Clearance of a persistent picornavirus infection is associated with enhanced pro-apoptotic and cellular immune responses

Long-term persistent viral infections cause substantial morbidity and associated economic losses in human and veterinary contexts. Yet, the mechanisms associated with establishment of persistent infections are poorly elucidated. We investigated immunomodulatory mechanisms associated with clearance versus persistence of foot-and-mouth disease virus (FMDV) in micro-dissected compartments of the bovine nasopharynx by microarray. The use of laser-capture microdissection allowed elucidation of differential gene regulation within distinct anatomic compartments critical to FMDV infection. Analysis of samples from transitional and persistent phases of infection demonstrated significant differences in transcriptome profiles of animals that cleared infection versus those that became persistently infected carriers. Specifically, it was demonstrated that clearance of FMDV from the nasopharyngeal mucosa was associated with upregulation of targets associated with activation of T cell-mediated immunity. Contrastingly, gene regulation in FMDV carriers suggested inhibition of T cell activation and promotion of Th2 polarization. These findings were corroborated by immunofluorescence microscopy which demonstrated relative abundance of CD8⁺ T cells in the nasopharyngeal mucosa in association with clearance of FMDV. The findings presented herein emphasize that a critical balance between Th1 and Th2 -mediated immunity is essential for successful clearance of FMDV infection and should be considered for development of next-generation vaccines and antiviral products.

Expression, purification and characterization of a catalytic domain of human protein tyrosine phosphatase non-receptor 12 (PTPN12) in Escherichia coli with FKBP-type PPIase as a chaperon

Protein tyrosine phosphatase non-receptor type 12 (PTPN12), also known as PTP-PEST, was broadly expressed in hemopoietic cells. Recent research has shown that this enzyme is involved in tumorigenesis, as well as in tumor progression and transfer, as it can suppress multiple oncogenic tyrosine kinases. However, the difficulty of soluble expression of PTP-PEST in prokaryotic cells has resulted in great limitations in investigating its structure and functions. In this study, we successfully carried out soluble expression of the catalytic domain of PTP-PEST (ΔPTP-PEST) in Escherichia coli and performed an enzymatic characterization and kinetics. To confirm expression efficiency, we also induced the expression of the chaperon, FKBP_C. FKBP_C expression indicated efficacious prokaryotic expression of ΔPTP-PEST. In conclusion, our work yielded a practical expression system and two-step chromatography purification method that may serve as a valuable tool for the structural and functional analysis of proteins that are difficult to express in the soluble form in prokaryotic cells.