Sequence-specific 1H, 13C and 15N backbone resonance assignments of the 34 kDa catalytic domain of human PTPN7

Novel Potential Therapeutic Targets of PTPN Families for Lung Cancer

Despite the treatment of lung adenocarcinoma (LUAD) having partially improved in recent years, LUAD patients still have poor prognosis rates. Therefore, it is especially important to explore effective biomarkers and exploit novel therapeutic developments. High-throughput technologies are widely used as systematic approaches to explore differences in expressions of thousands of genes for both biological and genomic systems. Recently, using big data analyses in biomedicine research by integrating several high-throughput databases and tools, including The Cancer Genome Atlas (TCGA), cBioportal, Oncomine, and Kaplan-Meier plotter, is an important strategy to identify novel biomarkers for cancer therapy. Here, we used two different comprehensive bioinformatics analysis and revealed protein tyrosine phosphatase non-receptor type (PTPN) family genes, especially PTPN1 and PTPN22, were downregulated in lung cancer tissue in comparison with normal samples. The survival curves indicated that LUAD patients with high transcription levels of PTPN5 were significantly associated with a good prognosis. Meanwhile, Gene Ontology (GO) and MetaCore analyses indicated that co-expression of the PTPN1, PTPN5, and PTPN21 genes was significantly enriched in cancer development-related pathways, including GTPase activity, regulation of small GTPase-mediated signal transduction, response to mechanical stimuli, vasculogenesis, organ morphogenesis, regulation of stress fiber assembly, mitogen-activated protein kinase (MAPK) cascade, cell migration, and angiogenesis. Collectively, this study revealed that PTPN family members are both significant prognostic biomarkers for lung cancer progression and promising clinical therapeutic targets, which provide new targets for treating LUAD patients.

1H, 15N and 13C sequence specific backbone assignment of the vanadate inhibited hematopoietic tyrosine phosphatase

The sequence-specific backbone assignment of hematopoietic protein tyrosine phosphatase (HePTP; PTPN7) in presence of vanadate has been determined, based on triple-resonance experiments using uniformly [¹³C,¹⁵N]-labeled protein. These assignments facilitate further studies of HePTP in the presence of inhibitors to target leukemia and provide further insights into the function of protein tyrosine phosphatases.

NMR Spectroscopy to Study MAP Kinase Binding to MAP Kinase Phosphatases

NMR spectroscopy and other solution methods are increasingly being used to obtain novel insights into the mechanisms by which MAPK regulatory proteins bind and direct the activity of MAPKs. Here, we describe how interactions between the MAPK p38α and its regulatory proteins are studied using NMR spectroscopy, isothermal titration calorimetry, and small angle X-ray scattering (SAXS).

The KIM-family protein-tyrosine phosphatases use distinct reversible oxidation intermediates: Intramolecular or intermolecular disulfide bond formation

The kinase interaction motif (KIM) family of protein-tyrosine phosphatases (PTPs) includes hematopoietic protein-tyrosine phosphatase (HePTP), striatal-enriched protein-tyrosine phosphatase (STEP), and protein-tyrosine phosphatase receptor type R (PTPRR). KIM-PTPs bind and dephosphorylate mitogen-activated protein kinases (MAPKs) and thereby critically modulate cell proliferation and differentiation. PTP activity can readily be diminished by reactive oxygen species (ROS), e.g. H₂O₂, which oxidize the catalytically indispensable active-site cysteine. This initial oxidation generates an unstable sulfenic acid intermediate that is quickly converted into either a sulfinic/sulfonic acid (catalytically dead and irreversible inactivation) or a stable sulfenamide or disulfide bond intermediate (reversible inactivation). Critically, our understanding of ROS-mediated PTP oxidation is not yet sufficient to predict the molecular responses of PTPs to oxidative stress. However, identifying distinct responses will enable novel routes for PTP-selective drug design, important for managing diseases such as cancer and Alzheimer's disease. Therefore, we performed a detailed biochemical and molecular study of all KIM-PTP family members to determine their H₂O₂ oxidation profiles and identify their reversible inactivation mechanism(s). We show that despite having nearly identical 3D structures and sequences, each KIM-PTP family member has a unique oxidation profile. Furthermore, we also show that whereas STEP and PTPRR stabilize their reversibly oxidized state by forming an intramolecular disulfide bond, HePTP uses an unexpected mechanism, namely, formation of a reversible intermolecular disulfide bond. In summary, despite being closely related, KIM-PTPs significantly differ in oxidation profiles. These findings highlight that oxidation protection is critical when analyzing PTPs, for example, in drug screening.

Sequence-specific backbone ¹H, ¹³C and ¹⁵N assignments of the 34 kDa catalytic domain of PTPN5 (STEP)

PTPN5 is a protein tyrosine phosphatase that plays an integral role in regulating excitatory postsynaptic activity. The sequence-specific backbone assignments of the murine PTPN5 catalytic domain have been determined based on triple-resonance experiments using uniformly [(2)H,(13)C,(15)N]-labeled protein.

Role of protein tyrosine phosphatase non-receptor type 7 in the regulation of TNF-α production in RAW 264.7 macrophages

Protein tyrosine phosphatases play key roles in a diverse range of cellular processes such as differentiation, cell proliferation, apoptosis, immunological signaling, and cytoskeletal function. Protein tyrosine phosphatase non-receptor type 7 (PTPN7), a member of the phosphatase family, specifically inactivates mitogen-activated protein kinases (MAPKs). Here, we report that PTPN7 acts as a regulator of pro-inflammatory TNF-α production in RAW 264.7 cells that are stimulated with lipopolysaccharide (LPS) that acts as an endotoxin and elicits strong immune responses in animals. Stimulation of RAW 264.7 cells with LPS leads to a transient decrease in the levels of PTPN7 mRNA and protein. The overexpression of PTPN7 inhibits LPS-stimulated production of TNF-α. In addition, small interfering RNA (siRNA) analysis showed that knock-down of PTPN7 in RAW 264.7 cells increased TNF-α production. PTPN7 has a negative regulatory function to extracellular signal regulated kinase 1/2 (ERK1/2) and p38 that increase LPS-induced TNF-α production in macrophages. Thus, our data presents PTPN7 as a negative regulator of TNF-α expression and the inflammatory response in macrophages.

Molecular basis of MAP kinase regulation

Mitogen-activated protein kinases (MAPKs; ERK1/2, p38, JNK, and ERK5) have evolved to transduce environmental and developmental signals (growth factors, stress) into adaptive and programmed responses (differentiation, inflammation, apoptosis). Almost 20 years ago, it was discovered that MAPKs contain a docking site in the C-terminal lobe that binds a conserved 13-16 amino acid sequence known as the D- or KIM-motif (kinase interaction motif). Recent crystal structures of MAPK:KIM-peptide complexes are leading to a precise understanding of how KIM sequences contribute to MAPK selectivity. In addition, new crystal and especially NMR studies are revealing how residues outside the canonical KIM motif interact with specific MAPKs and contribute further to MAPK selectivity and signaling pathway fidelity. In this review, we focus on these recent studies, with an emphasis on the use of NMR spectroscopy, isothermal titration calorimetry and small angle X-ray scattering to investigate these processes.

Structural basis of p38α regulation by hematopoietic tyrosine phosphatase

MAP kinases regulate essential cellular events, including cell growth, differentiation and inflammation. The solution structure of a complete MAPK-MAPK-regulatory protein complex, p38α-HePTP, was determined, enabling a comprehensive investigation of the molecular basis of specificity and fidelity in MAPK regulation. Structure determination was achieved by combining NMR spectroscopy and small-angle X-ray scattering data with a new ensemble calculation-refinement procedure. We identified 25 residues outside of the HePTP kinase interaction motif necessary for p38α recognition. The complex adopts an extended conformation in solution and rarely samples the conformation necessary for kinase deactivation. Complex formation also does not affect the N-terminal lobe, the activation loop of p38α or the catalytic domain of HePTP. Together, these results show how the downstream tyrosine phosphatase HePTP regulates p38α and provide for fundamentally new insights into MAPK regulation and specificity.