2. Academic Validation
  3. The Megacomplex protects ER-alpha from degradation by Fulvestrant in epithelial ovarian cancer

The Megacomplex protects ER-alpha from degradation by Fulvestrant in epithelial ovarian cancer

  • Cancer Lett. 2024 Jul 22:217129. doi: 10.1016/j.canlet.2024.217129.
Sushil Kumar Jaiswal 1,  Kevin Fedkenheuer 1,  Ronak Khamar 1,  Hua Tan 1,  Valer Gotea 1,  Sonam Raj 2,  Michael Fedkenheuer 3,  Abdel Elkahloun 4,  Ming Zhao 5,  Lisa M Jenkins 6,  Christina M Annunziata 7,  Laura Elnitski 8
Affiliations

Affiliations

  • 1 Translational and Functional Genomics Branch, National Human Genome Research Institute, Bethesda, MD 20892.
  • 2 Genitourinary Malignancies Branch, National Cancer Institute, Bethesda, MD 20892.
  • 3 Genomics and Immunity Section, National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD 20892.
  • 4 Microarrays and Single-Cell Genomics Core, National Human Genome Research Institute, Bethesda, MD 20892.
  • 5 HPLC Core, National Institute of Allergy and Infectious Diseases, Rockville, MD 20852.
  • 6 Mass Spec Core, National Cancer Institute, Bethesda, MD 20892.
  • 7 Women's Malignancies Branch, National Cancer Institute, Bethesda, MD 20892.
  • 8 Translational and Functional Genomics Branch, National Human Genome Research Institute, Bethesda, MD 20892. Electronic address: Elnitski@nih.gov.
PMID: 39048045 DOI: 10.1016/j.canlet.2024.217129
Abstract

Ovarian Cancer, a significant contributor to cancer-related mortality, exhibits limited responsiveness to hormonal therapies targeting the Estrogen Receptor (ERα). This study aimed to elucidate the mechanisms behind ERα resistance to the therapeutic drug Fulvestrant (ICI182780 or ICI). Notably, compared to the cytoplasmic version, nuclear ERα was minimally degraded by ICI, suggesting a mechanism for drug resistance via the protective confines of the nuclear substructures. Of these substructures, we identified a 1.3MDa Megacomplex comprising transcription factors ERα, FOXA1, and PITX1 using size exclusion chromatography (SEC) in the ovarian Cancer cell line, PEO4. ChIP-seq revealed these factors colocalized at 6,775 genomic positions representing sites of Megacomplex formation. Megacomplex ERα exhibited increased resistance to degradation by ICI compared to cytoplasmic and nuclear ERα. A small molecule inhibitor of active chromatin and super-enhancers, JQ1, in combination with ICI significantly enhanced ERα degradation from Megacomplex as revealed by SEC and ChIP-seq. Interestingly, this combination degraded both the cytoplasmic as well as nuclear ERa. Pathway enrichment analysis showed parallel results for RNA-seq gene sets following Estradiol, ICI, or ICI plus JQ1 treatments as those defined by Megacomplex binding identified through ChIP-seq. Furthermore, similar pathway enrichments were confirmed in mass-spec analysis of the Megacomplex macromolecule fractions after modulation by Estradiol or ICI. These findings implicate Megacomplex in ERα-driven ovarian Cancer chromatin regulation. This combined treatment strategy exhibited superior inhibition of cell proliferation and viability. Therefore, by uncovering ERα's resistance within the Megacomplex, the combined ICI plus JQ1 treatment elucidates a novel drug treatment vulnerability.

Keywords

BRD4 inhibitor; ChIP-seq; Estrogen receptor; ICI182780; JQ1; Megacomplex; drug resistance; gel filtration; ovarian cancer; super-enhancer.

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