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Methylation of the epigenetic regulator KMT2D by SMYD2 contributes to therapeutic response in hormone-dependent breast cancer [KMT2D_KI_RNA]

ABSTRACT: Activating mutations in PIK3CA, the gene encoding PI3Kα, are frequently found in estrogen receptor (ER+) breast cancer and the combination of the PI3K inhibitor alpelisib with the anti-ER agent fulvestrant is approved for therapy. We have uncovered a key role for the chromatin modifier KMT2D in regulating the ER-PI3K crosstalk. PI3Kα effectors, AKT and SGK, negatively regulate KMT2D through S1331 phosphorylation. When PI3K is inhibited, this regulatory event is lost, leading to increased chromatin recruitment of KMT2D and an upregulation of ER-dependent transcription. Here we discovered a previously undescribed methylation site on KMT2D, at K1330 directly adjacent to S1331, catalyzed by the lysine methyltransferase SMYD2. SMYD2 loss attenuates alpelisib-induced KMT2D chromatin binding. Accordingly, loss of SMYD2 abrogates alpelisib-induced changes in gene expression, including ER-dependent transcription. Knockdown or pharmacological inhibition of SMYD2 sensitizes breast cancer cells, patient-derived organoids, and tumors to PI3K/AKT inhibition and endocrine therapy in part through KMT2D K1330 methylation. Methyl dead knock-in clones of KMT2D phenocopy many of the effects of SMYD2 inhibition on cell and tumor growth, drug response, and transcriptional output. Together, our findings uncover a regulatory cross-talk between posttranslational modifications that plays an important role in fine-tuning the functions of KMT2D at the chromatin. This provides a rationale for epigenetic therapy using SMYD2 inhibitors in combination with PI3Kα/AKT inhibitors for the treatment of ER+/PIK3CA mutant breast cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE253958 | GEO | 2024/05/04

REPOSITORIES: GEO

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Project description:Activating mutations of PIK3CA are the most frequent genomic alterations in estrogen receptor (ER)-positive breast tumors and selective PI3Kα inhibitors are in clinical development. The activity of these agents, however, is not homogenous and only a fraction of patients bearing PIK3CA-mutant ER-positive tumors benefit from single agent administration. Searching for mechanisms of resistance, we observed that suppression of PI3K signaling with different agents results in induction of ER-dependent transcriptional activity as demonstrated by changes in expression in genes containing ER binding sites, enhanced ER transcription and increased occupancy by the ER of promoter regions of upregulated genes. Furthermore, expression of ESR1 mRNA and ER protein levels themselves were also increased upon PI3K inhibition. These changes in gene expression were confirmed in vivo in xenograft and patient derived models and in tumors from patients undergoing treatment with the PI3Kα inhibitor BYL719. The observed effects on transcription were enhanced by the addition of estradiol and suppressed by the anti-ER therapies fulvestrant and tamoxifen. Fulvestrant markedly sensitized ER-positive tumors to PI3Kα inhibition. We propose that increased ER transcriptional activity may be a compensatory mechanism that limits the activity of PI3K inhibitors and that combined PI3K and ER inhibition is a rational approach to target these tumors. The aim of our study was to explore the mechanism by which combination of PI3K pathway inhibitors and estrogen receptor function blockade results in superior antitumor activity. We aimed to evaluate whether changes in ER function were influencing the clinical response to anti-PI3K therapy in ER-positive breast tumors that harbor PI3K pathway activation. For this purpose, we planned to use various specific PI3K inhibitors, namely: BYL719 (p110α specific catalytic inhibitor), GDC0941 (pan-PI3K inhibitor), GDC0032 and BAY80-6946 (p110sparing PI3K inhibitors) in a panel of ER-positive breast cancer cell lines and xenografts that harbor PIK3CA activating mutations. We also used MK2206 (pan-AKT allosteric inhibitor) to inhibit the PI3K pathway in ER-positive cell lines which activate this pathway through PTEN loss. Finally, in order to evaluate the role of ER up-regulation as a pro-survival signal in our in vitro and in vivo models, we planned to use the selective ER modulator 4-hydroxy-tamoxifen (4-OHT) and degrader fulvestrant. For the in vivo experiments, the number of animals in each group was calculated to measure a 25% difference between the means of placebo and treatment groups with a power of 80% and a p value of 0.01. Host mice carrying xenografts were randomly and equally assigned to either control or treatment groups. Animal experiments were conducted in a controlled and non-blinded manner. Moreover, we evaluated by means of RNAseq gene expression changes breast cancer patients that underwent BYL719 based therapy to validate our in vitro findings in terms of ER expression. In vitro experiments were performed at least two times and at least in triplicate for each replica.

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Methylation of the epigenetic regulator KMT2D by SMYD2 contributes to therapeutic response in hormone-dependent breast cancer [KMT2D_KI_RNA]

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