Phosphotyrosine phosphatase R3 receptors: Origin, evolution and structural diversification

Inhibition of VE-PTP rejuvenates Schlemm's canal in aged mice and acts via Tie2

PURPOSE

Glaucoma is the leading cause of irreversible blindness worldwide and is associated with high intraocular pressure (IOP). Schlemm's canal (SC), a hybrid vessel present in the anterior part of the eye, is known to control IOP by draining aqueous humor into the systemic circulation. Formation and function of SC is supported by the tyrosine kinase receptor Tie2. Likewise, inhibition of the vascular endothelial protein tyrosine phosphatase (VE-PTP), which associates with Tie2 has similar effects. However, VE-PTP also targets VE-cadherin and several other substrates. Here, we analyzed whether Tie2 is indeed the major substrate which is responsible for the role of VE-PTP in SC function. In addition, we analyzed the function of VE-PTP in SC of the aged eye in mice.

METHODOLOGY

We tested the effects of the VE-PTP inhibitor AKB9778 and of VE-PTP gene inactivation on SC area and IOP in WT and in Tie2iLEC/SC-KO and VE-cadherin-Y685F mutant mice.

RESULTS

Pharmacologic inhibition of VE-PTP with AKB9778 increased SC area only in mice expressing Tie2. The VE-cadherin-Y685F mutation had neither an effect on SC area nor on the effects of AKB9778 on SC formation. Induced VE-PTP gene inactivation in adult mice had similar effects as AKB9778. Furthermore, we could show that AKB9778 improved SC function in aged mice as judged by increasing SC area and lowering of IOP.

CONCLUSION

Interference with VE-PTP function improves SC function in a strictly Tie2 dependent way and pharmacologic inhibition of VE-PTP with AKB9778 is a promising approach for improving SC function in the aged eye.

An in-line method for high-throughput screening of protein tyrosine phosphatase receptor type O inhibitors by capillary electrophoresis based on electrophoretically mediated microanalysis

Protein tyrosine phosphatase receptor type O (PTPRO) plays an important role in inflammation-related pathways and has become an emerging drug target. In this study, we developed an in-line capillary electrophoresis (CE) method for the investigation of the enzymatic activity of PTPRO, which was based on electrophoretically mediated microanalysis (EMMA). After a thorough method validation of the optimized conditions, this protocol was successfully employed to determine the kinetics of PTPRO as well as the half-maximal inhibitory concentration (IC50) of two typical PTPRO inhibitors. The final results were consistent with the values obtained through classical ultraviolet-visible (UV-vis) spectrophotometry. Our new method exhibited improved accuracy and reduced consumption, avoiding the disadvantages of traditional methods. This work provides a new strategy for PTPRO enzyme kinetic studies as well as inhibitory activity determination through capillary electrophoresis for the first time.

Origin and Evolution of RAS Membrane Targeting

KRAS, HRAS and NRAS proto-oncogenes belong to a family of 40 highly homologous genes, which in turn are a subset of a superfamily of >160 genes encoding small GTPases. RAS proteins consist of a globular G-domain (aa1-166) and a 22-23 aa unstructured hypervariable region (HVR) that mediates membrane targeting. The evolutionary origins of the RAS isoforms, their HVRs and alternative splicing of the KRAS locus has not been explored. We found that KRAS is basal to the RAS proto-oncogene family and its duplication generated HRAS in the common ancestor of vertebrates. In a second round of duplication HRAS generated NRAS and KRAS generated an additional RAS gene we have designated KRASBL, absent in mammals and birds. KRAS4A arose through a duplication and insertion of the 4th exon of NRAS into the 3rd intron of KRAS. We found evolutionary conservation of a short polybasic region (PBR1) in HRAS, NRAS and KRAS4A, a second polybasic region (PBR2) in KRAS4A, two neutralized basic residues (NB) and a serine in KRAS4B and KRASBL, and a modification of the CaaX motif in vertebrates with farnesyl rather than geranylgeranyl polyisoprene lipids, suggesting that a less hydrophobic membrane anchor is critical to RAS protein function. The persistence of four RAS isoforms through >400 million years of evolution argues strongly for differential function.

Hereditable variants of classical protein tyrosine phosphatase genes: Will they prove innocent or guilty?

Protein tyrosine phosphatases, together with protein tyrosine kinases, control many molecular signaling steps that control life at cellular and organismal levels. Impairing alterations in the genes encoding the involved proteins is expected to profoundly affect the quality of life-if compatible with life at all. Here, we review the current knowledge on the effects of germline variants that have been reported for genes encoding a subset of the protein tyrosine phosphatase superfamily; that of the thirty seven classical members. The conclusion must be that the newest genome research tools produced an avalanche of data that suggest 'guilt by association' for individual genes to specific disorders. Future research should face the challenge to investigate these accusations thoroughly and convincingly, to reach a mature genotype-phenotype map for this intriguing protein family.

Origin and evolution of RAS oncoprotein membrane targeting

KRAS, HRAS and NRAS oncogenes belong to a family of 40 highly homologous genes, which in turn are a subset of a superfamily of >160 genes encoding small GTPases. RAS oncoproteins consist of a globular G-domain (aa1-166) and a 22-23aa unstructured hypervariable region (HVR) that mediates membrane targeting. The evolutionarily origins of the RAS isoforms, their HVRs and alternative splicing of the KRAS locus has not been explored. We found that KRAS is basal to the oncogene family and its duplication generated HRAS in the common ancestor of vertebrates. In a second round of duplication HRAS generated NRAS and KRAS generated an additional RAS gene we have designated KRASBL, absent in mammals and birds. KRAS4A arose through a duplication and insertion of the 4th exon of NRAS into the 3rd intron of KRAS. We found evolutionarily conservation of a short polybasic region (PBR1) in HRAS, NRAS and KRAS4A, a second polybasic region (PBR2) in KRAS4A, two neutralized basic residues (NB) and a serine in KRAS4B and KRASBL, and a modification of the CaaX motif in vertebrates with farnesyl rather than geranylgeranyl polyisoprene lipids, suggesting that a less hydrophobic membrane anchor is critical to RAS oncoprotein function. The persistence of four RAS isoforms through >400 MY of evolution argues strongly for differential function.

Protein Tyrosine Phosphatases in Neuroblastoma: Emerging Roles as Biomarkers and Therapeutic Targets

Neuroblastoma is a type of cancer intimately related with early development and differentiation of neuroendocrine cells, and constitutes one of the pediatric cancers with higher incidence and mortality. Protein tyrosine phosphatases (PTPs) are key regulators of cell growth and differentiation by their direct effect on tyrosine dephosphorylation of specific protein substrates, exerting major functions in the modulation of intracellular signaling during neuron development in response to external cues driving cell proliferation, survival, and differentiation. We review here the current knowledge on the role of PTPs in neuroblastoma cell growth, survival, and differentiation. The potential of PTPs as biomarkers and molecular targets for inhibition in neuroblastoma therapies is discussed.

Vascular Endothelial Protein Tyrosine Phosphatase Regulates Endothelial Function

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is a receptor-type PTP (RPTP), predominantly expressed in vascular endothelial cells. It regulates embryonic and tumor angiogenesis and controls vascular permeability and homeostasis in inflammation. Major substrates are the tyrosine kinase receptor Tie-2 and the adhesion molecule VE-cadherin. This review describes how VE-PTP controls vascular functions by its various substrates and the therapeutic potential of VE-PTP in various pathophysiological settings.

PTPRO predicts patient prognosis and correlates with immune infiltrates in human clear cell renal cell carcinoma

BACKGROUND

The tumor-suppressive role of protein tyrosine phosphatase receptor type O (PTPRO) has been described in a variety of human cancers; however, the clinical significance of PTPRO in human clear cell renal cell carcinoma (ccRCC) remains unclear.

METHODS

PTPRO expression in renal cell carcinoma (RCC) was analyzed via the Oncomine database, Gene Expression Omnibus (GEO) datasets, and The Cancer Genome Atlas (TCGA) datasets. The Kaplan-Meier curves and Cox proportional hazards model were used to evaluate the relationship of PTPRO with overall survival in ccRCC. Gene ontology (GO) analysis and gene set enrichment analysis (GSEA) were performed to explore the signaling pathways in which PTPRO may be involved. The correlation between PTPRO and immune infiltrates in ccRCC was investigated via Tumor Immune Estimation Resource (TIMER) database. The association between PTPRO mRNA expression and its methylation in RCC was analyzed using the Cancer Cell Line Encyclopedia (CCLE) dataset, GEO dataset, and cBioPortal database. The impact of PTPRO methylation on overall survival was estimated by the MethSurv database.

RESULTS

We showed that the expression of PTPRO was significantly lower in human RCC. Moreover, the lower expression of PTPRO was associated with worse overall survival in ccRCC, particularly in the advanced stage patients. Multivariate Cox regression analysis revealed the expression of PTPRO as an independent prognostic predictor for overall survival of ccRCC. Of note, PTPRO was found to be associated with the activation of immune signaling and immune cell infiltration. Furthermore, methylation of PTPRO was prevalently observed in ccRCC, and methylation of PTPRO predicted the poor outcome of ccRCC.

CONCLUSIONS

Our findings suggested that PTPRO at both RNA and DNA methylation levels had the potential as a prognostic biomarker for predicting prognosis, and PTPRO expression was closely associated with immune infiltration in ccRCC patients.

LncRNA HULC promotes lung squamous cell carcinoma by regulating PTPRO via NF-κB

Accumulating studies have implicated that long noncoding RNA (lncRNA) plays a vital role in lung cancer. However, little is known of the role of lncRNA highly upregulated in liver cancer (HULC) in the pathogenesis of lung squamous cell carcinoma (LSCC). In this study, we investigated the modifying effects and underlying mechanisms of lncRNA HULC in LSCC. Significantly decreased level of lncRNA HULC was observed in LSCC samples compared with adjacent tissues. Besides, the expression of lncRNA HULC was negatively associated with protein tyrosine phosphatase receptor type O (PTPRO) in LSCC. Moreover, lncRNA HULC could promote the proliferation of LSCC cells by downregulating the expression PTPRO dependent on the phosphorylation and activation of nuclear factor-κB (NF-κB). The present study firstly shows strong evidence supporting a critical role of lncRNA HULC in promoting LSCC by regulating PTPRO/NF-κB signaling pathway, which provides new promising biomarkers for LSCC.