Dual-specificity phosphatases as molecular targets for inhibition in human disease

Transcriptome Profiles of Human Lung Epithelial Cells A549 Interacting with Aspergillus fumigatus by RNA-Seq

Lung epithelial cells constitute the first defense line of host against the inhaled Aspergillus fumigatus; however, the transcriptional response of human alveolar type II epithelial cells was still unclear. Here we used RNA-Seq technology to assess the transcriptome profiles of A549 cells following direct interaction with conidia of A. fumigatus. The total number of identified genes was 19118. Compared with uninfected A549 cells, 459 genes were differentially expressed in cells co-incubated with conidia for 8 h, including 302 up-regulated genes and 157 down-regulated genes. GO and KEGG pathway enrichment analysis showed that most of the up-regulated genes were related to immune response, chemotaxis and inflammatory response and enriched in cytokine-cytokine receptor interaction, JAK-STAT and MAPK signaling pathways. The down-regulated genes were mainly enriched for terms associated with development, hemopoiesis and ion transport. Among them, EGR4 and HIST1H4J gene had the maximum of fold change in up-regulated and down-regulated genes, respectively. Fourteen up-regulated genes and three down-regulated genes were further validated and significant increase on expression of IL-6, IL-8 and TNF-α in A549 cells were confirmed by qRT-PCR during the interaction of A549 cells with A. fumigatus. Besides, western blot showed that expression of two proteins (ARC, EGR1) significantly increased in A549 cells during interaction with A. fumigatus conidia for 8h. Interference of endogenous expression of ARC or EGR1 protein in A549 cells reduced the internalization of A. fumigatus. These results provided important insights into dynamic changes of gene expression in lung epithelial cells, especially its strong immunological response against A. fumigatus infection.

Procyanidins Negatively Affect the Activity of the Phosphatases of Regenerating Liver

Natural polyphenols like oligomeric catechins (procyanidins) derived from green tea and herbal medicines are interesting compounds for pharmaceutical research due to their ability to protect against carcinogenesis in animal models. It is nevertheless still unclear how intracellular pathways are modulated by polyphenols. Monomeric polyphenols were shown to affect the activity of some protein phosphatases (PPs). The three phosphatases of regenerating liver (PRLs) are close relatives and promising therapeutic targets in cancer. In the present study we show that several procyanidins inhibit the activity of all three members of the PRL family in the low micromolar range, whereas monomeric epicatechins show weak inhibitory activity. Increasing the number of catechin units in procyanidins to more than three does not further enhance the potency. Remarkably, the tested procyanidins showed selectivity in vitro when compared to other PPs, and over 10-fold selectivity toward PRL-1 over PRL-2 and PRL-3. As PRL overexpression induces cell migration compared to control cells, the effect of procyanidins on this phenotype was studied. Treatment with procyanidin C2 led to a decrease in cell migration of PRL-1- and PRL-3-overexpressing cells, suggesting the compound-dependent inhibition of PRL-promoted cell migration. Treatment with procyanidin B3 led to selective suppression of PRL-1 overexpressing cells, thereby corroborating the selectivity toward PRL-1- over PRL-3 in vitro. Together, our results show that procyanidins negatively affect PRL activity, suggesting that PRLs could be targets in the polypharmacology of natural polyphenols. Furthermore, they are interesting candidates for the development of PRL-1 inhibitors due to their low cellular toxicity and the selectivity within the PRL family.

Blockade of dual-specificity phosphatase 28 decreases chemo-resistance and migration in human pancreatic cancer cells

Pancreatic cancer remains one of the most deadly cancers, with a grave prognosis. Despite numerous endeavors to improve treatment of the neoplasm, limited progress has been made. In the present study, we investigated the role of dual specificity phosphatase 28 (DUSP28) in relation to anti-cancer drug sensitivity and migratory activity in human pancreatic cancer cells for the first time. Analysis using Universal exPress Codes (UPCs) with the GEO database showed significantly higher DUSP28 mRNA expression in pancreatic cancers. We found that DUSP28 was highly expressed in several human pancreatic cancer cell lines that showed resistance to anti-cancer drugs. Overexpression of DUSP28 decreased anti-cancer drug-sensitivity and enhanced cellular migration via the ERK1/2 pathway in DUSP28-negative cell lines. Knockdown of DUSP28 re-sensitized cells to anti-cancer drugs even at sublethal doses by inducing an apoptotic pathway and significantly reduced migration in DUSP28-positive human pancreatic cancer cell lines. Furthermore, DUSP28-positive cell line (Panc-1) xenograft models were more resistant to gemcitabine treatment than DUSP28-negative cell line (SNU-213) xenograft models. Collectively, these results indicate that DUSP28 plays a key role in drug resistance and migratory activity in human pancreatic cells, and suggest that targeting DUSP28 might have clinical relevance in eradicating malignant pancreatic cancers.

Perspective: Tyrosine phosphatases as novel targets for antiplatelet therapy

Arterial thrombosis is the primary cause of most cases of myocardial infarction and stroke, the leading causes of death in the developed world. Platelets, highly specialized cells of the circulatory system, are key contributors to thrombotic events. Antiplatelet drugs, which prevent platelets from aggregating, have been very effective in reducing the mortality and morbidity of these conditions. However, approved antiplatelet therapies have adverse side effects, most notably the increased risk of bleeding. Moreover, there remains a considerable incidence of arterial thrombosis in a subset of patients receiving currently available drugs. Thus, there is a pressing medical need for novel antiplatelet agents with a more favorable safety profile and less patient resistance. The discovery of novel antiplatelet targets is the matter of intense ongoing research. Recent findings demonstrate the potential of targeting key signaling molecules, including kinases and phosphatases, to prevent platelet activation and aggregation. Here, we offer perspectives to targeting members of the protein tyrosine phosphatase (PTP) superfamily, a major class of enzymes in signal transduction. We give an overview of previously identified PTPs in platelet signaling, and discuss their potential as antiplatelet drug targets. We also introduce VHR (DUSP3), a PTP that we recently identified as a major player in platelet biology and thrombosis. We review our data on genetic deletion as well as pharmacological inhibition of VHR, providing proof-of-principle for a novel and potentially safer VHR-based antiplatelet therapy.

Structure of human dual-specificity phosphatase 7, a potential cancer drug target

Human dual-specificity phosphatase 7 (DUSP7/Pyst2) is a 320-residue protein that belongs to the mitogen-activated protein kinase phosphatase (MKP) subfamily of dual-specificity phosphatases. Although its precise biological function is still not fully understood, previous reports have demonstrated that DUSP7 is overexpressed in myeloid leukemia and other malignancies. Therefore, there is interest in developing DUSP7 inhibitors as potential therapeutic agents, especially for cancer. Here, the purification, crystallization and structure determination of the catalytic domain of DUSP7 (Ser141-Ser289/C232S) at 1.67 Å resolution are reported. The structure described here provides a starting point for structure-assisted inhibitor-design efforts and adds to the growing knowledge base of three-dimensional structures of the dual-specificity phosphatase family.

VHR/DUSP3 phosphatase: structure, function and regulation

Vaccinia H1-related (VHR) phosphatase, also known as dual-specificity phosphatase (DUSP) 3, is a small member of the DUSP (also called DSP) family of phosphatases. VHR has a preference for phospho-tyrosine substrates, and has important roles in cellular signaling ranging from cell-cycle regulation and the DNA damage response to MAPK signaling, platelet activation and angiogenesis. VHR/DUSP3 has been implicated in several human cancers, where its tumor-suppressing and -promoting properties have been described. We give a detailed overview of VHR/DUSP3 phosphatase and compare it with its most closely related phosphatases DUSP13B, DUSP26 and DUSP27.

Structural analysis of human dual-specificity phosphatase 22 complexed with a phosphotyrosine-like substrate

4-Nitrophenyl phosphate (p-nitrophenyl phosphate, pNPP) is widely used as a small molecule phosphotyrosine-like substrate in activity assays for protein tyrosine phosphatases. It is a colorless substrate that upon hydrolysis is converted to a yellow 4-nitrophenolate ion that can be monitored by absorbance at 405 nm. Therefore, the pNPP assay has been widely adopted as a quick and simple method to assess phosphatase activity and is also commonly used in assays to screen for inhibitors. Here, the first crystal structure is presented of a dual-specificity phosphatase, human dual-specificity phosphatase 22 (DUSP22), in complex with pNPP. The structure illuminates the molecular basis for substrate binding and may also facilitate the structure-assisted development of DUSP22 inhibitors.