HIF-1–mediated PPME1 expression promotes breast cancer progression via AKT activation and β-catenin recruitment
Yajing Lyu, Varen Talwar, Yongkang Yang, Si-Sim Kang, Shuyi Li, Shaima Salman, Daiana Drehmer, Yufeng Wang, Chelsey Chen, Vijay Ramu, Sujin Kim, Dylan Park, Tina Yi-Ting Huang, Emmanuel Datan, Dominic Dordai, Jonathan P. Schneck, Gregg L. Semenza
Yajing Lyu, Varen Talwar, Yongkang Yang, Si-Sim Kang, Shuyi Li, Shaima Salman, Daiana Drehmer, Yufeng Wang, Chelsey Chen, Vijay Ramu, Sujin Kim, Dylan Park, Tina Yi-Ting Huang, Emmanuel Datan, Dominic Dordai, Jonathan P. Schneck, Gregg L. Semenza
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Research Article Genetics Oncology

HIF-1–mediated PPME1 expression promotes breast cancer progression via AKT activation and β-catenin recruitment

Abstract

Hypoxia-inducible factor 1 (HIF-1) orchestrates the transcriptional regulation of thousands of genes involved in breast cancer (BC) progression. Here, we identified protein phosphatase 2A (PP2A) methylesterase 1 (PPME1) as a critical HIF-1 target gene that drives oncogenic signaling under hypoxic conditions. In BC cells, HIF-1–dependent PPME1 expression caused inhibition of the PP2A catalytic subunit (PP2Ac), thereby diminishing PP2A activity, which led to AKT activation, phosphorylation of β-catenin, and its nuclear translocation. Nuclear β-catenin cooperates with HIF-1 to promote BC stem cell specification by activating transcription of the NANOG and KLF4 genes, which encode pluripotency factors, and to drive immune evasion by activating transcription of VEGFA, which recruits and polarizes immunosuppressive tumor-associated macrophages and ISG20, which represses STAT1/IRF1-dependent expression of CXCL10, thereby impairing CD8+ T cell recruitment. In vivo, PPME1 knockdown altered the tumor immune microenvironment, enhanced antitumor immunity, and synergized with anti–CTLA-4 immunotherapy to enable complete tumor eradication. These findings establish PPME1 as a critical regulator linking hypoxia signaling, stemness, and immune evasion and highlight its potential as a BC therapeutic target in combination with immune checkpoint blockade.

Authors

Yajing Lyu, Varen Talwar, Yongkang Yang, Si-Sim Kang, Shuyi Li, Shaima Salman, Daiana Drehmer, Yufeng Wang, Chelsey Chen, Vijay Ramu, Sujin Kim, Dylan Park, Tina Yi-Ting Huang, Emmanuel Datan, Dominic Dordai, Jonathan P. Schneck, Gregg L. Semenza

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Figure 1

PPME1 expression is mediated by HIF-1 in hypoxic BC cells.

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PPME1 expression is mediated by HIF-1 in hypoxic BC cells. (A) Human BC ...
(A) Human BC cell lines were exposed to 20% or 1% O2 for 24 hours, and PPME1 mRNA expression was analyzed by RT-qPCR. For each cell line, the expression of PPME1 mRNA was normalized to the mean result for MDA-MB-231 cells at 20% O2. ****P < 0.0001, 2-way ANOVA with Tukey’s multiple comparisons test. (B) BC cell lines were exposed to 20% or 1% O2 for 48 hours, whole cell lysates were prepared, and immunoblot assays were performed. (C) Comparison of the expression levels of 17 mRNAs encoded by HIF target genes (HIF metagene signature) in BCs that ranked in the top 100 (high) or bottom 100 (low) in TCGA database with respect to PPME1 mRNA expression. **P < 0.01, Wilcoxon test. (D–G) MDA-MB-231 (D and E) and MCF7 (F and G) subclones, which stably expressed a nontargeting control shRNA (NTC) or shRNA targeting HIF-1α, HIF-2α, or both HIF-1α and HIF-2α (DKD), were exposed to 20% or 1% O2 for 24 or 48 hours, followed by RT-qPCR (D and F) or immunoblot assay (E and G), respectively. **P < 0.01, ****P < 0.0001; 2-way ANOVA with Tukey’s multiple comparisons test. (H) ChIP-seq analysis of SUM159 cells revealed overlapping matches to the HIF consensus binding site 5′-(A/G)CGTG-3′ (highlighted in red) under the HIF-1α peak in the PPME1 gene at +92 bp relative to the transcription start site using the Integrative Genomics Viewer genome browser. (I and J) MDA-MB-231 (I) and MCF7 (J) cells were exposed to 20% or 1% O2 for 16 hours, and ChIP assays were performed using antibodies against HIF-1α, HIF-1β, or HIF-2α. Primers flanking the candidate HIF binding site were used for qPCR, and results were normalized to the mean result at 20% O2. **P < 0.01, ***P < 0.001, ****P < 0.0001, 2-tailed Student’s t test. In all bar graphs, data are presented as mean ± SD (n = 3).