PP2A-dependent TFEB activation is blocked by PIKfyve-induced mTORC1 activity

Transcriptional factor EB (TFEB) is a master regulator of genes required for autophagy and lysosomal function. The nuclear localization of TFEB is blocked by the mechanistic target of rapamycin complex 1 (mTORC1)-dependent phosphorylation of TFEB at multiple sites including Ser-211. Here we show that inhibition of PIKfyve, which produces phosphatidylinositol 3,5-bisphosphate on endosomes and lysosomes, causes a loss of Ser-211 phosphorylation and concomitant nuclear localization of TFEB. We found that while mTORC1 activity toward S6K1, as well as other major mTORC1 substrates, is not impaired, PIKfyve inhibition specifically impedes the interaction of TFEB with mTORC1. This suggests that mTORC1 activity on TFEB is selectively inhibited due to loss of mTORC1 access to TFEB. In addition, we found that TFEB activation during inhibition of PIKfyve relies on the ability of protein phosphatase 2A (PP2A) but not calcineurin/PPP3, to dephosphorylate TFEB Ser-211. Thus, when PIKfyve is inhibited, PP2A is dominant over mTORC1 for control of TFEB phosphorylation at Ser-S211. Together these findings suggest that mTORC1 and PP2A have opposing roles on TFEB via phosphorylation and dephosphorylation of Ser-211, respectively, and further, that PIKfyve inhibits TFEB activity by facilitating mTORC1-dependent phosphorylation of TFEB.

Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A): Could It Be a Promising Biomarker and Therapeutic Target in Parkinson’s Disease?

Parkinson’s disease (PD) is an incurable neurodegenerative disease characterized by aggregation of pathological alpha-synuclein (α-syn) and loss of dopaminergic neuron in the substantia nigra. Inhibition of phosphorylation of the α-syn has been shown to mediate alleviation of PD-related pathology. Protein phosphatase 2A (PP2A), an important serine/threonine phosphatase, plays an essential role in catalyzing dephosphorylation of the α-syn. Here, we identified and validated cancerous inhibitor of PP2A (CIP2A), as a potential diagnostic biomarker for PD. Our data showed that plasma CIP2A concentrations in PD patients were significantly lower compared to age- and sex-matched controls, 1.721 (1.435–2.428) ng/ml vs 3.051(2.36–5.475) ng/ml, p < 0.0001. The area under the curve of the plasma CIP2A in distinguishing PD from the age- and sex-matched controls was 0.776. In addition, we evaluated the role of CIP2A in PD-related pathogenesis in PD cellular and MPTP-induced mouse model. The results demonstrated that CIP2A is upregulated in PD cellular and MPTP-induced mouse models. Besides, suppression of the CIP2A expression alleviates rotenone induced aggregation of the α-syn as well as phosphorylation of the α-syn in SH-SY5Y cells, which is associated with increased PP2A activity. Taken together, our data demonstrated that CIP2A plays an essential role in the mechanisms related to PD development and might be a novel PD biomarker.

Protein phosphatase 2A inactivation induces microsatellite instability, neoantigen production and immune response

Microsatellite-instable (MSI), a predictive biomarker for immune checkpoint blockade (ICB) response, is caused by mismatch repair deficiency (MMRd) that occurs through genetic or epigenetic silencing of MMR genes. Here, we report a mechanism of MMRd and demonstrate that protein phosphatase 2A (PP2A) deletion or inactivation converts cold microsatellite-stable (MSS) into MSI tumours through two orthogonal pathways: (i) by increasing retinoblastoma protein phosphorylation that leads to E2F and DNMT3A/3B expression with subsequent DNA methylation, and (ii) by increasing histone deacetylase (HDAC)2 phosphorylation that subsequently decreases H3K9ac levels and histone acetylation, which induces epigenetic silencing of MLH1. In mouse models of MSS and MSI colorectal cancers, triple-negative breast cancer and pancreatic cancer, PP2A inhibition triggers neoantigen production, cytotoxic T cell infiltration and ICB sensitization. Human cancer cell lines and tissue array effectively confirm these signaling pathways. These data indicate the dual involvement of PP2A inactivation in silencing MLH1 and inducing MSI.

Specification of the Okadaic Acid Equivalent for Okadaic Acid, Dinophysistoxin-1, and Dinophysistoxin-2 Based on Protein Phosphatase 2A Inhibition and Cytotoxicity Assays Using Neuro 2A Cell Line

Diarrhetic shellfish poisoning (DSP) is a globally occurring disease threatening public health and trade. The causative toxins, okadaic acid (OA), dinophysistoxin-1 (DTX1), and dinophysistoxin-2 (DTX2) are collectively called OAs, and are quantified using the LC-MS/MS method. The hazardous effect of total OAs is expressed as the sum of OA equivalents defined for respective OAs based on mouse lethality, produced by either intraperitoneal (OAip) or oral administration (OAor). OAs are potent inhibitors of protein phosphatase 2A (PP2A) and are cytotoxic, necessitating expansion of the concept of OA equivalents to all relevant bioactivities. In this study, we determined OA equivalents for respective OA members in PP2A inhibition and cytotoxicity assays. To secure result credibility, we used certified OAs, reference materials, and PP2A produced using genetic engineering. The relative ratio of the OA equivalents determined by PP2A inhibition assays for OA, DTX1, and DTX2 were 1.0:1.6:0.3, while the ratio determined using the cytotoxicity assays indicated 1.0:1.5:0.5. OA equivalents showed a similar tendency in the PP2A inhibition and cytotoxicity assays, and matched better with oral toxicity data than intraperitoneal toxicity in mice. The PP2A inhibition assay, which measures the core activity of the OAs, suggested a higher OA equivalent for DTX1 than that currently used.

Cellular Protein Phosphatase 2A Regulates Cell Survival Mechanisms in Influenza A Virus Infection

Influenza A viruses (IAVs) are respiratory pathogens that are able to hijack multiple cellular mechanisms to drive their replication. Consequently, several viral and cellular proteins undergo posttranslational modifications such as dynamic phosphorylation/dephosphorylation. In eukaryotic cells, dephosphorylation is mainly catalyzed by protein phosphatase 2A (PP2A). While the function of kinases in IAV infection is quite well studied, only little is known about the role of PP2A in IAV replication. Here, we show, by using knockdown and inhibition approaches of the catalytic subunit PP2Ac, that this phosphatase is important for efficient replication of several IAV subtypes. This could neither be attributed to alterations in the antiviral immune response nor to changes in transcription or translation of viral genes. Interestingly, decreased PP2Ac levels resulted in a significantly reduced cell viability after IAV infection. Comprehensive kinase activity profiling identified an enrichment of process networks related to apoptosis and indicated a synergistic action of hyper-activated PI3K/Akt, MAPK/JAK-STAT and NF-kB signaling pathways, collectively resulting in increased cell death. Taken together, while IAV seems to effectively tap leftover PP2A activity to ensure efficient viral replication, reduced PP2Ac levels fail to orchestrate cell survival mechanisms to protect infected cells from early cell death.