A nuclear protein tyrosine phosphatase induces shortening of G1 phase and increase in c-Myc protein level

PTPN18 promotes colorectal cancer progression by regulating the c-MYC-CDK4 axis

Protein tyrosine phosphatase non-receptor type 18 (PTPN18) is often highly expressed in colorectal cancer (CRC), but its role in this disease remains unclear. We demonstrated that PTPN18 overexpression promotes growth and tumorigenesis in CRC cells and that PTPN18 deficiency yields the opposite results in vitro. Moreover, a xenograft assay showed that PTPN18 deficiency significantly inhibited tumorigenesis in vivo. PTPN18 activated the MYC signaling pathway and enhanced CDK4 expression, which is tightly associated with the cell cycle and proliferation in cancer cells. Finally, we found that MYC interacted with PTPN18 and increased the protein level of MYC. In conclusion, our results suggest that PTPN18 promotes CRC development by stabilizing the MYC protein level, which in turn activates the MYC-CDK4 axis. Thus, PTPN18 could be a novel therapeutic target in the future.

The Role of Protein Tyrosine Phosphatases in Inflammasome Activation

Inflammasomes are multi-protein complexes that mediate the activation and secretion of the inflammatory cytokines IL-1β and IL-18. More than half a decade ago, it has been shown that the inflammasome adaptor molecule, ASC requires tyrosine phosphorylation to allow effective inflammasome assembly and sustained IL-1β/IL-18 release. This finding provided evidence that the tyrosine phosphorylation status of inflammasome components affects inflammasome assembly and that inflammasomes are subjected to regulation via kinases and phosphatases. In the subsequent years, it was reported that activation of the inflammasome receptor molecule, NLRP3, is modulated via tyrosine phosphorylation as well, and that NLRP3 de-phosphorylation at specific tyrosine residues was required for inflammasome assembly and sustained IL-1β/IL-18 release. These findings demonstrated the importance of tyrosine phosphorylation as a key modulator of inflammasome activity. Following these initial reports, additional work elucidated that the activity of several inflammasome components is dictated via their phosphorylation status. Particularly, the action of specific tyrosine kinases and phosphatases are of critical importance for the regulation of inflammasome assembly and activity. By summarizing the currently available literature on the interaction of tyrosine phosphatases with inflammasome components we here provide an overview how tyrosine phosphatases affect the activation status of inflammasomes.

Genetic variants of PTPN2 are associated with lung cancer risk: a re-analysis of eight GWASs in the TRICL-ILCCO consortium

The T-cell protein tyrosine phosphatase (TCPTP) pathway consists of signaling events mediated by TCPTP. Mutations and genetic variants of some genes in the TCPTP pathway are associated with lung cancer risk and survival. In the present study, we first investigated associations of 5,162 single nucleotide polymorphisms (SNPs) in 43 genes of this TCPTP pathway with lung cancer risk by using summary data of six published genome-wide association studies (GWAS) of 12,160 cases and 16,838 controls. We identified 11 independent SNPs in eight genes after correction for multiple comparisons by a false discovery rate <0.20. Then, we performed in silico functional analyses for these 11 SNPs by eQTL analysis, two of which, PTPN2 SNPs rs2847297 and rs2847282, were chosen as tagSNPs. We further included two additional GWAS datasets of Harvard University (984 cases and 970 controls) and deCODE (1,319 cases and 26,380 controls), and the overall effects of these two SNPs among all eight GWAS studies remained significant (OR = 0.95, 95% CI = 0.92-0.98, and P = 0.004 for rs2847297; OR = 0.95, 95% CI = 0.92-0.99, and P = 0.009 for rs2847282). In conclusion, the PTPN2 rs2847297 and rs2847282 may be potential susceptible loci for lung cancer risk.

Dynamics of mitochondria during the cell cycle

Mitochondria are highly dynamic organelles in eukaryotic cells. Although the role of mitochondria in metabolism, ATP production and apoptosis is more widely recognized, alterations in mitochondrial morphology and abundance are also important for cellular functions. Here we investigated mitochondrial dynamics in synchronized HeLa cells in which the major stages of the cell cycle of the observed cells were resolved by staining phosphorylate histones H1 and H3, and showed that mitochondria exist as filamentous network structures throughout the cell cycle progression, changing their morphology, distribution, and abundance. The current results suggest that mitochondrial condensation occurred at prophase is required for the proper progression of mitochondrial division.

A nuclear protein tyrosine phosphatase activates p53 and induces caspase-1-dependent apoptosis

PTP-S2/TC45 is a nuclear protein tyrosine phosphatase, which induces p53-dependent apoptosis. Here we show that the p53 protein level increased in MCF-7 cells in response to PTP-S2 overexpression. PTP-S2-induced p53 protein was transcriptionally active and it could activate caspase-1 gene expression from endogenous as well as ectopic promoter. Coexpression of an active site mutant of procaspase-1 strongly inhibited PTP-S2-induced apoptosis. Mutant procaspase-1 also inhibited apoptosis induced by p53 overexpression or doxorubicin treatment, which induce caspase-1 gene expression. In contrast, apoptosis induced by staurosporine or cycloheximide, which do not increase caspase-1 gene expression, was not affected by mutant procaspase-1. These results suggest that caspase-1 may be one of the mediators of p53-dependent apoptosis in human cells.

Inhibition of anchorage-independent cell growth, adhesion, and cyclin D1 gene expression by a dominant negative mutant of a tyrosine phosphatase

PTP-S4/TC48 protein tyrosine phosphatase is localized in the nuclear and cytoplasmic membranes. To investigate the role of PTP-S4 in cell growth, adhesion, and transformation, normal and a catalytically inactive mutant form of this phosphatase were expressed in polyoma virus-transformed F111 fibroblast cell line, PyF. Expression of mutant PTP-S4 in PyF cells resulted in strong inhibition of anchorage-independent growth in soft agar but had no significant effect on growth in liquid culture. Tumor formation in nude mice was also reduced by mutant PTP-S4. Expression of normal PTP-S4 in PyF cells significantly increased anchorage-independent cell growth and tumor formation in nude mice. Overexpression of catalytically inactive mutant of PTP-S2/TC45 (a splice variant of PTP-S4 that is nuclear) did not inhibit anchorage-independent growth of PyF cells. Mutant PTP-S4-expressing cells were inhibited in adhesion and spreading on tissue culture plates compared to control cells. Expression of mutant PTP-S4 in PyF cells reduced the levels of cyclin D1 and cyclin A mRNA, whereas cyclin D2 mRNA level was not affected significantly. Expression of antisense cyclin D1 strongly inhibited anchorage-independent growth. Inhibition of anchorage-independent growth by mutant PTP-S4 was overcome to a large extent by coexpression of cyclin D1. These results suggest that mutant PTP-S4 inhibits anchorage-independent growth and adhesion of polyoma virus-transformed cells by interfering with the normal function of PTP-S4 upstream of cyclin D1 gene expression.