Search

Summary Estrogen receptor-α (ER) drives tumor development in ER-positive (ER+) breast cancer. The transcription factor GATA3 has been closely linked to ER function, but its precise role in this setting remains unclear. Quantitative proteomics was used to assess changes to the ER complex in response to GATA3 depletion. Unexpectedly, few proteins were lost from the ER complex in the absence of GATA3, with the only major change being depletion of the dioxygenase TET2. TET2 binding constituted a near-total subset of ER binding in multiple breast cancer models, with loss of TET2 associated with reduced activation of proliferative pathways. TET2 knockdown did not appear to change global methylated cytosine (5mC) levels; however, oxidation of 5mC to 5-hydroxymethylcytosine (5hmC) was significantly reduced, and these events occurred at ER enhancers. These findings implicate TET2 in the maintenance of 5hmC at ER sites, providing a potential mechanism for TET2-mediated regulation of ER target genes., Graphical Abstract, Highlights • TET2 is identified as a component of the ER complex through depletion of GATA3 • TET2 global chromatin binding tracks that of ER/GATA3 in multiple breast cancer models • Loss of TET2 is linked to dysregulated expression of ER target genes • Concurrent loss of 5hmC at ER sites provides insights into TET2’s role in ER activity, Broome et al. use quantitative proteomics and chromatin immunoprecipitation to explore the contribution of TET2 to ER/GATA3 transcriptional activity. TET2 tracks ER chromatin binding in breast cancer models and plays an essential role in the maintenance of 5-hydroxymethylcytosine at ER enhancers, revealing a role for TET2 in ER-driven gene expression.

The cytokine interleukin-6 (IL6) and its downstream effector STAT3 constitute a key oncogenic pathway, which has been thought to be functionally connected to estrogen receptor α (ER) in breast cancer. We demonstrate that IL6/STAT3 signaling drives metastasis in ER+ breast cancer independent of ER. STAT3 hijacks a subset of ER enhancers to drive a distinct transcriptional program. Although these enhancers are shared by both STAT3 and ER, IL6/STAT3 activity is refractory to standard ER-targeted therapies. Instead, inhibition of STAT3 activity using the JAK inhibitor ruxolitinib decreases breast cancer invasion in vivo. Therefore, IL6/STAT3 and ER oncogenic pathways are functionally decoupled, highlighting the potential of IL6/STAT3-targeted therapies in ER+ breast cancer.

Estrogen Receptor alpha (ERα) plays a major role in most breast cancers, and it is the target of endocrine therapies used in the clinic as standard of care for women with breast cancer expressing this receptor. The two methods ChIP-seq (chromatin immunoprecipitation coupled with deep sequencing) and RIME (Rapid Immunoprecipitation of Endogenous Proteins) have greatly improved our understanding of ERα function during breast cancer progression and in response to anti-estrogens. A critical component of both ChIP-seq and RIME protocols is the antibody that is used against the bait protein. To date, most of the ChIP-seq and RIME experiments for the study of ERα have been performed using the sc-543 antibody from Santa Cruz Biotechnology. However, this antibody has been discontinued, thereby severely impacting the study of ERα in normal physiology as well as diseases such as breast cancer and ovarian cancer. Here, we compare the sc-543 antibody with other commercially available antibodies, and we show that 06-935 (EMD Millipore) and ab3575 (Abcam) antibodies can successfully replace the sc-543 antibody for ChIP-seq and RIME experiments.

Understanding the dynamics of endogenous protein–protein interactions in complex networks is pivotal in deciphering disease mechanisms. To enable the in-depth analysis of protein interactions in chromatin-associated protein complexes, we have previously developed a method termed RIME (Rapid Immunoprecipitation Mass spectrometry of Endogenous proteins). Here, we present a quantitative multiplexed method (qPLEX-RIME), which integrates RIME with isobaric labelling and tribrid mass spectrometry for the study of protein interactome dynamics in a quantitative fashion with increased sensitivity. Using the qPLEX-RIME method, we delineate the temporal changes of the Estrogen Receptor alpha (ERα) interactome in breast cancer cells treated with 4-hydroxytamoxifen. Furthermore, we identify endogenous ERα-associated proteins in human Patient-Derived Xenograft tumours and in primary human breast cancer clinical tissue. Our results demonstrate that the combination of RIME with isobaric labelling offers a powerful tool for the in-depth and quantitative characterisation of protein interactome dynamics, which is applicable to clinical samples., Chromatin-associated protein complexes play a critical role in the regulation of gene expression in health and disease. Here, the authors describe a sensitive mass spectrometry-based method to monitor the dynamic interactions of endogenous chromatin-associated protein complexes in clinical samples.

Nuclear receptors (NRs) are key transcriptional regulators of metazoan physiology and metabolism. Different NRs bind to similar or even identical core response elements; however, they regulate transcription in a highly receptor- and gene-specific manner. These differences in gene activation can most likely be accounted for by mechanisms involving receptor-specific interactions with DNA as well as receptor-specific interactions with protein complexes binding to adjacent and distant DNA sequences. Here, we review key molecular aspects of transactivation by NRs with special emphasis on the recent advances in the molecular mechanisms responsible for receptor- and gene-specific transcriptional activation. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

SUMMARY Transcription factors have recently been shown to colocalize in hotspot regions of the genome, which are further clustered into super-enhancers. However, the detailed molecular organization of transcription factors at hotspot regions is poorly defined. Here, we have used digital genomic footprinting to precisely define factor localization at a genome-wide level during the early phase of 3T3-L1 adipocyte differentiation, which allows us to obtain detailed molecular insight into how transcription factors target hotspots. We demonstrate the formation of ATF-C/EBP heterodimers at a composite motif on chromatin, and we suggest that this may be a general mechanism for integrating external signals on chromatin. Furthermore, we find evidence of extensive recruitment of transcription factors to hotspots through alternative mechanisms not involving their known motifs and demonstrate that these alternative binding events are functionally important for hotspot formation and activity. Taken together, these findings provide a framework for understanding transcription factor cooperativity in hotspots.