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The progression of hepatocellular carcinoma (HCC) is coincident with aberrant splicing of numerous tumor‐related genes. Identification of the tumor‐specific splice variants that facilitate HCC metastasis may provide a more comprehensive insight into the mechanisms of HCC metastasis. Through RNA sequencing and bioinformatic analyses, PPM1G was identified as a biomarker associated with HCC metastasis. Our data mapped a transcriptome‐wide landscape of alternative splicing events modulated by PPM1G in HCC. Notably, we characterized the exon six‐skipping transcript of TBL1X as an onco‐splice variant regulated by PPM1G. Experimental validation revealed the enrichment of TBL1X‐S in response to PPM1G overexpression. Moreover, mRNA stability analyses revealed that PPM1G prolonged the half‐life of the TBL1X‐S transcript. Both PPM1G and TBL1X‐S exhibited metastasis‐promoting phenotypes, with PPM1G‐driven metastasis in HCC being partially dependent on TBL1X‐S. Mechanistically, different TBL1X splice variants showed varying affinities for ZEB1, with TBL1X‐S significantly enhancing ZEB1 activation and repressing CDH1 transcription, potentially accelerating the epithelial‐mesenchymal transition (EMT) process. In conclusion, our study highlights the biological role of PPM1G and TBL1X‐S in tumor metastasis. The PPM1G/TBL1X‐S signaling axis presents a new view for investigating liver cancer metastasis mechanisms. In this study, we highlight the biological role of the PPM1G and TBL1X‐S variants in tumor metastasis. The PPM1G/TBL1X‐S signaling axis presents a new view for investigating liver cancer metastasis mechanisms.

Inducible transcriptional programs mediate the regulation of key biological processes and organismal functions. Despite their complexity, cells have evolved mechanisms to precisely control gene programs in response to environmental cues to regulate cell fate and maintain normal homeostasis. Upon stimulation with proinflammatory cytokines such as tumor necrosis factor-α (TNF), the master transcriptional regulator nuclear factor (NF)-κB utilizes the PPM1G/PP2Cγ phosphatase as a coactivator to normally induce inflammatory and cell survival programs. However, how PPM1G activity is precisely regulated to control NF-κB transcription magnitude and kinetics remains unknown. Here, we describe a mechanism by which the ARF tumor suppressor binds PPM1G to negatively regulate its coactivator function in the NF-κB circuit thereby promoting insult resolution. ARF becomes stabilized upon binding to PPM1G and forms a ternary protein complex with PPM1G and NF-κB at target gene promoters in a stimuli-dependent manner to provide tunable control of the NF-κB transcriptional program. Consistently, loss of ARF in colon epithelial cells leads to up-regulation of NF-κB antiapoptotic genes upon TNF stimulation and renders cells partially resistant to TNF-induced apoptosis in the presence of agents blocking the antiapoptotic program. Notably, patient tumor data analysis validates these findings by revealing that loss of ARF strongly correlates with sustained expression of inflammatory and cell survival programs. Collectively, we propose that PPM1G emerges as a therapeutic target in a variety of cancers arising from ARF epigenetic silencing, to loss of ARF function, as well as tumors bearing oncogenic NF-κB activation.

Ten–eleven translocation protein 1 (TET1) functions as an epigenetic regulatory molecule, mediating the majority of DNA demethylation, and plays a role in the development of different types of cancers by regulating the expression of proto‐oncogenes and oncogenes. Here it is found that TET1 is highly expressed in cholangiocarcinoma (CCA) and is associated with a poor prognosis. In addition, TET1 promotes claudin‐3 (CLDN3) transcription by targeting the CLDN3 promoter region between −16 and 512 for demethylation. PPM1G functions as a protein dephosphorylase, catalyzing the dephosphorylation of TET1. This results in the destabilization of the TET1 protein, thereby impairing the targeting of the CLDN3 promoter for demethylation. Two phosphatase inhibitors, staurosporine and AZD0156, inhibit epithelial‐to‐mesenchymal transition (EMT) in cholangiocarcinoma cells by suppressing TET1 expression. In conclusion, it is also demonstrated that PPM1G can be employed as a therapeutic target to impede the progression of CCA by catalyzing the dephosphorylation of TET1, which diminishes the capacity of TET1 to target the CLDN3 promoter to activate transcription and inhibit EMT in CCA. Ten–eleven translocation protein 1 (TET1) exerts its pro‐carcinogenic effect in cholangiocarcinoma by catalyzing the demethylation of the claudin‐3 (CLDN3) promoter region. This effect is impaired by dephosphorylation of TET1 by PPM1G, destabilizing the TET1 protein. In addition, two phosphorylation inhibitors, staurosporine and AZD0156, inhibit cholangiocarcinoma progression by destabilizing the protein by inhibiting TET1 phosphorylation.

Hypoxia-inducible factors (HIFs) are key regulators of hypoxic responses, and their stability and transcriptional activity are controlled by several kinases. However, the regulation of HIF by protein phosphatases has not been thoroughly investigated. Here, we found that overexpression of Mg2+/Mn2+-dependent protein phosphatase 1 gamma (PPM1G), one of Ser/Thr protein phosphatases, downregulated protein expression of ectopic HIF-1α under normoxic or acute hypoxic conditions. In addition, the deficiency of PPM1G upregulated protein expression of endogenous HIF-1α under normoxic or acute oxidative stress conditions. PPM1G decreased expression of HIF-1α via the proteasomal pathway. PPM1G-mediated HIF-1α degradation was dependent on prolyl hydroxylase (PHD), but independent of von Hippel-Lindau (VHL). These data suggest that PPM1G is critical for the control of HIF-1α-dependent responses.