Project description:Current clinical guidelines suggest that breast cancers with low hormone receptor expression (LowHR) in 1% to 10% of tumor cells should be regarded as hormone receptor positive tumors. However, clinical data shows that patients with such tumors have a worse outcome compared to patients with hormone receptor expression above 10 %. Further, gene expression studies suggest that these tumors have a TNBC-like signature similar to triple negative breast cancers (TNBC). The goal of this study was to use DNA methylation-based classification to clarify the status for this infrequent but important patient subgroup. We performed whole genome DNA methylation profiling on 23 LowHR breast cancer specimens, including 13 samples with HER2 amplification and compared our results with a reference breast cancer cohort from The Cancer Genome Atlas. Unsupervised clustering and dimensionality reduction revealed that breast cancers with low hormone receptor expression that lacked HER2 amplification usually clustered with TNBC reference samples (8/10; “LowHR TNBC-like”). In contrast, most specimens with low hormone receptor expression and HER2 amplification grouped with hormone receptor positive cancers (11/13; “LowHR HRpos-like”). We observed highly similar DNA methylation patterns of LowHR TNBC-like samples and true TNBCs with almost no differential methylation. Furthermore, the Ki67 proliferation index of LowHR TNBC-like samples as well as clinical outcome parameters were more similar to TNBCs and differed from LowHR_HRpos-like cases. We here demonstrate that LowHR breast cancer comprises two molecularly distinct groups that can be separated by DNA methylation profiling. More clinical data is required for a definite classification of these tumors, but our data strongly suggests that LowHR TNBC-like samples are molecularly, histologically and clinically closely related to TNBC, while LowHR HRpos-like specimens are closely related to hormone receptor positive tumors.
Project description:Naive pluripotent epiblast cells of the preimplantation murine embryo and their in vitro counterpart, embryonic stem (ES) cells, have the capacity to give rise to all cells of the adult. Such developmental plasticity is associated with global genome hypomethylation. It is unclear whether genome methylation is dynamically regulated only via differential expression of DNA methyltransferases (DNMTs) and Ten-eleven Translocation (TET) enzymes, which oxidase methylated DNA. Here we show that LIF/Stat3 signalling induces genomic hypomethylation via metabolic reconfiguration. In Stat3-/- ES cells we observed decreased alpha-ketoglutarate (ɑKG) production from reductive Glutamine metabolism, leading to decreased TET activity, increased Dnmt3a/b expression and to a global increase in DNA methylation. Notably, genome methylation is dynamically controlled by simply modulating αKG availability, mitochondrial activity or Stat3 activation in mitochondria, indicating effective crosstalk between metabolism and the epigenome. Stat3-/- ES cells also show increased methylation at Imprinting Control Regions accompanied with differential expression of >50% of imprinted genes. Single-cell transcriptome analysis of Stat3-/- embryos confirmed dysregulated expression of Dnmt3a/b, Tet2, and imprinted genes in vivo. Our results reveal that the LIF/Stat3 signal bridges the metabolic and epigenetic profiles of naive pluripotent cells, ultimately controlling genome methylation and imprinted gene expression. Several imprinted genes regulate cell proliferation and are often misregulated in tumors. Moreover, a wide range of cancers display Stat3-overactivation, raising the possibility that the molecular module we described here is exploited under pathological conditions.