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Foamy viruses are members of the Retroviridae family's Spumaretrovirinae subfamily. They induce cell vacuolation and exhibit a foamy pathogenic impact after infecting cells. DACH1 (dachshund family transcription factor 1) is a crucial cytokine linked to tumor development, and is associated with the growth of many different malignant tumor cells. Additionally, DACH1 suppresses pancreatic cell proliferation and is involved in diabetes insulin signaling. Prototype foamy viruses (PFVs) were used for the investigation of the regulatory mechanism of FVs on cellular DACH1 expression. The results show that DACH1 expression in PFV-infected cells was inconsistent at both the transcriptional and protein levels. At the transcriptional level, DACH1 was significantly activated by PFV transactivator Tas, and dual-luciferase reporter gene tests, EMSA, and ChIP assays found a Tas response element of 21 nucleotides in the DACH1 promoter. PFV and Tas did not boost the levels of DACH1 protein in a manner consistent with the high levels of DACH1 transcription expression. It was noted that Tas increased the expression of the Ser/Thr protein phosphatase PPM1E, causing PPM1E-mediated post-translational SUMOylation alterations of DACH1 to prompt DACH1 to degrade. The reason for DACH1 protein degradation is that DACH1 inhibits PFV replication. To sum up, these findings show that PFV upregulated the transcription of DACH1, while urging its protein into PPM1E-mediated SUMOylation, to eliminate the adverse effect of DACH1 overexpression of host cells on viral replication and promote virus survival. [ABSTRACT FROM AUTHOR]

Foamy viruses belong to the Spumaretrovirinae subfamily member of the Retroviridae family and produce nonpathogenic infection to hosts in the natural conditions. However, infections of foamy viruses can dramatically cause severe cytopathic effects in vitro. To date, the exact molecular mechanism has remained unclear which implied the tremendous importance of virus-host cell immune reactions. In this study, we found that the transactivator Tas in two foamy viruses isolated from Old World Monkey (OWM) induced obvious inhibition of cell proliferation via the upregulation of Foxo3a expression. It was mediated by the generation of ROS and the initiation of ER stress, and ultimately, the mitochondrial apoptosis pathway was triggered. Notably, PFV Tas contributed to the accumulation of G0/G1 phase cycle arrest induced by the activation of the p53 signaling pathway and the nuclear transportation of HDAC4 via upregulating PPM1E expression. Together, these results demonstrated the different survival strategies by which foamy virus can hijack host cell cytokines and regulate virus-host cell interactions.

Foamy viruses are members of the Retroviridae family’s Spumaretrovirinae subfamily. They induce cell vacuolation and exhibit a foamy pathogenic impact after infecting cells. DACH1 (dachshund family transcription factor 1) is a crucial cytokine linked to tumor development, and is associated with the growth of many different malignant tumor cells. Additionally, DACH1 suppresses pancreatic cell proliferation and is involved in diabetes insulin signaling. Prototype foamy viruses (PFVs) were used for the investigation of the regulatory mechanism of FVs on cellular DACH1 expression. The results show that DACH1 expression in PFV-infected cells was inconsistent at both the transcriptional and protein levels. At the transcriptional level, DACH1 was significantly activated by PFV transactivator Tas, and dual-luciferase reporter gene tests, EMSA, and ChIP assays found a Tas response element of 21 nucleotides in the DACH1 promoter. PFV and Tas did not boost the levels of DACH1 protein in a manner consistent with the high levels of DACH1 transcription expression. It was noted that Tas increased the expression of the Ser/Thr protein phosphatase PPM1E, causing PPM1E-mediated post-translational SUMOylation alterations of DACH1 to prompt DACH1 to degrade. The reason for DACH1 protein degradation is that DACH1 inhibits PFV replication. To sum up, these findings show that PFV upregulated the transcription of DACH1, while urging its protein into PPM1E-mediated SUMOylation, to eliminate the adverse effect of DACH1 overexpression of host cells on viral replication and promote virus survival.

Foamy viruses belong to the Spumaretrovirinae subfamily member of the Retroviridae family and produce nonpathogenic infection to hosts in the natural conditions. However, infections of foamy viruses can dramatically cause severe cytopathic effects in vitro . To date, the exact molecular mechanism has remained unclear which implied the tremendous importance of virus-host cell immune reactions. In this study, we found that the transactivator Tas in two foamy viruses isolated from Old World Monkey (OWM) induced obvious inhibition of cell proliferation via the upregulation of Foxo3a expression. It was mediated by the generation of ROS and the initiation of ER stress, and ultimately, the mitochondrial apoptosis pathway was triggered. Notably, PFV Tas contributed to the accumulation of G0/G1 phase cycle arrest induced by the activation of the p53 signaling pathway and the nuclear transportation of HDAC4 via upregulating PPM1E expression. Together, these results demonstrated the different survival strategies by which foamy virus can hijack host cell cytokines and regulate virus-host cell interactions.

Abstract: Activation of 5′-AMP-activated protein kinase (AMPK) is believed to be the mechanism by which the pharmaceuticals, metformin and phenformin, exert their beneficial effects for treatment of type 2 diabetes. These biguanide drugs elevate 5′-AMP, which allosterically activates AMPK and promotes phosphorylation on Thr172 of AMPK catalytic α subunits. Although kinases phosphorylating this site have been identified, phosphatases that dephosphorylate it are unknown. The aim of this study is to identify protein phosphatase(s) that dephosphorylate AMPKα-Thr172 within cells. Our initial data indicated that members of the protein phosphatase ce:sup>/ce:sup>/Mn2+-dependent (PPM) family and not those of the PPP family of protein serine/threonine phosphatases may be directly or indirectly inhibited by phenformin. Using antibodies raised to individual Ppm phosphatases that facilitated the assessment of their activities, phenformin stimulation of cells was found to decrease the ce:sup>/ce:sup>/Mn2+-dependent protein serine/threonine phosphatase activity of Ppm1E and Ppm1F, but not that attributable to other PPM family members, including Ppm1A/PP2Cα. Depletion of Ppm1E, but not Ppm1A, using lentiviral-mediated stable gene silencing, increased AMPKα-Thr172 phosphorylation approximately three fold in HEK293 cells. In addition, incubation of cells with low concentrations of phenformin and depletion of Ppm1E increased AMPK phosphorylation synergistically. Ppm1E and the closely related Ppm1F interact weakly with AMPK and assays with lysates of cells stably depleted of Ppm1F suggests that this phosphatase contributes to dephosphorylation of AMPK. The data indicate that Ppm1E and probably PpM1F are in cellulo AMPK phosphatases and that Ppm1E is a potential anti-diabetic drug target. [ABSTRACT FROM AUTHOR]

The current study tested the potential neuroprotective function of Tanshinone IIA (ThIIA) in neuronal cells with oxygen-glucose deprivation (ODG) and re-oxygenation (OGDR). In SH-SY5Y neuronal cells and primary murine cortical neurons, ThIIA pre-treatment attenuated OGDR-induced viability reduction and apoptosis. Further, OGDR-induced mitochondrial depolarization, reactive oxygen species production, lipid peroxidation and DNA damages in neuronal cells were significantly attenuated by ThIIA. ThIIA activated AMP-activated protein kinase (AMPK) signaling, which was essential for neuroprotection against OGDR. AMPKα1 knockdown or complete knockout in SH-SY5Y cells abolished ThIIA-induced AMPK activation and neuroprotection against OGDR. Further studies found that ThIIA up-regulated microRNA-135b to downregulate the AMPK phosphatase Ppm1e. Notably, knockdown of Ppm1e by targeted shRNA or forced microRNA-135b expression also activated AMPK and protected SH-SY5Y cells from OGDR. Together, AMPK activation by ThIIA protects neuronal cells from OGDR. microRNA-135b-mediated silence of Ppm1e could be the key mechanism of AMPK activation by ThIIA., Competing Interests: CONFLICTS OF INTEREST The authors declare no conflicts of interest.

Activation of AMP-activated protein kinase (AMPK) is a valuable anti-cancer strategy. In the current study, we tested expression and potential function of Ca2+/calmodulin-dependent protein kinase phosphatase (Ppm1E), an AMPKα phosphatase, in human gastric cancers. Ppm1E expression was elevated in human gastric cancer tissues (vs. normal tissues), which was correlated with AMPK (p-AMPKα, Thr-172) dephosphorylation and mTOR complex 1 (mTORC1) activation. Ppm1E upregulation, AMPK inhibition and mTORC1 activation were also observed in human gastric cancer cell lines (AGS, HGC-27, and SNU601). Intriguingly, Ppm1E knockdown by shRNA induced AMPK activation, mTORC1 inactivation, and proliferation inhibition in AGS cells. On the other hand, forced over-expression of Ppm1E induced further AMPK inhibition and mTORC1 activation to enhance AGS cell proliferation. Remarkably, microRNA-135b-5p ("miR-135b-5p"), an anti-Ppm1E microRNA, was downregulated in both human gastric cancer tissues and cells. Reversely, miR-135b-5p exogenous expression caused Ppm1E depletion, AMPK activation, and AGC cell proliferation inhibition. Together, Ppm1E upregulation in human gastric cancer is important for cell proliferation, possible via regulating AMPK-mTOR signaling.

Forced-activation of AMP-activated protein kinase (AMPK) can possibly inhibit osteoblastoma cells. Here, we aim to provoke AMPK activation via microRNA silencing its phosphatase Ppm1e (protein phosphatase Mg2+/Mn2+-dependent 1e). We showed that microRNA-135b-5p ("miR-135b-5p"), the anti-Ppm1e microRNA, was significantly downregulated in human osteoblastoma tissues. It was correlated with Ppm1e upregulation and AMPKα1 de-phosphorylation. Forced-expression of miR-135b-5p in human osteoblastoma cells (MG-63 and U2OS lines) silenced Ppm1e, and induced a profound AMPKα1 phosphorylation (at Thr-172). Osteoblastoma cell proliferation was inhibited after miR-135b-5p expression. Intriguingly, Ppm1e shRNA knockdown similarly induced AMPKα1 phosphorylation, causing osteoblastoma cell proliferation. Reversely, AMPKα1 shRNA knockdown or dominant negative mutation almost abolished miR-135b-5p's actions in osteoblastoma cells. Further in vivo studies demonstrated that U2OS tumor growth in mice was dramatically inhibited after expressing miR-135b-5p or Ppm1e shRNA. Together, our results suggest that miR-135b-induced Ppm1e silence induces AMPK activation to inhibit osteoblastoma cell proliferation.

AMPK activation in monocytes could suppress lipopolysaccharide (LPS)-induced tissue-damaging TNFa production. We are set to provoke AMPK activation via microRNA ("miRNA") downregulating its phosphatase Ppm1e. In human U937 and THP-1 monocytes, forced expression of microRNA-135b-5p ("miR-135b-5p") downregulated Ppm1e and activated AMPK signaling. Further, LPS-induced TNFα production in above cells was dramatically attenuated. Ppm1e shRNA knockdown in U937 cells also activated AMPK and inhibited TNFα production by LPS. AMPK activation is required for miR-135b-induced actions in monocytes, AMPKα shRNA knockdown or T172A dominant negative mutation almost abolished miR-135b-5p's suppression on LPS-induced TNFα production. Significantly, miR-135b-5p inhibited LPS-induced reactive oxygen species (ROS) production, NFκB activation and TNFα mRNA expression in human macrophages. AMPKα knockdown or mutation again abolished above actions by miR-135b-5p. We conclude that miR-135b-5p expression downregulates Ppm1e to activate AMPK signaling, which inhibits LPS-induced TNFα production via suppressing ROS production and NFκB activation.