Mediator of DNA Damage Checkpoint 1 (MDC1) Is a Novel Estrogen Receptor Coregulator in Invasive Lobular Carcinoma of the Breast

Abstract

Invasive lobular carcinoma (ILC) is the most common special histologic subtype of breast cancer, and nearly all ILC tumors express estrogen receptor alpha (ER). However, clinical and laboratory data suggest ILC are strongly estrogen-driven but not equally antiestrogen-sensitive. We hypothesized ILC-specific ER coregulators mediate ER functions and antiestrogen resistance in ILC, and profiled ER-associated proteins by mass spectrometry. Three ER+ ILC cell lines (MDA MB 134VI, SUM44PE, and BCK4) were compared with ER+ invasive ductal carcinoma (IDC) line data, and we examined whether siRNA of identified proteins suppressed ER-driven proliferation in ILC cells. This identified mediator of DNA damage checkpoint 1 (MDC1), a tumor suppressor in DNA damage response (DDR), as a novel ER coregulator in ILC. We confirmed ER:MDC1 interaction was specific to ILC versus IDC cells, and found MDC1 knockdown suppressed ILC cell proliferation and tamoxifen resistance. Using RNA-sequencing, we found in ILC cells MDC1 knockdown broadly dysregulates the ER transcriptome, with ER:MDC1 target genes enriched for promoter hormone response elements. Importantly, our data are inconsistent with MDC1 tumor suppressor functions in DDR, but suggest a novel oncogenic role for MDC1 as an ER coregulator. Supporting this, in breast tumor tissue microarrays, MDC1 protein was frequently low or absent in IDC, but MDC1 loss was rare in ER+ ILC. ER:MDC1 interaction and MDC1 coregulator functions may underlie ER function in ILC and serve as targets to overcome antiestrogen resistance in ILC. Implications: MDC1 has novel ER coregulator activity in ILC, which may underlie ILC-specific ER functions, estrogen response, and antiestrogen resistance.

WNT4 regulates cellular metabolism via intracellular activity at the mitochondria in breast and gynecologic cancers

“…To first examine the role for ER in regulation of metabolism in ILC cells, we integrated metabolomics data with gene expression data in MM134 following ER knockdown [37], and performed joint pathway analysis of metabolites (n=63; Figure 3B ) and genes (n=5322) dysregulated by ESR1 siRNA ( Supplemental File 3 ). Consistent with the central role for ER in cell proliferation, integrated pathway analysis showed enrichment in biosynthetic pathways, as well as glycolysis, the TCA cycle, and fatty acid metabolism ( Figure 3B ).…”

“…To examine how ER-mediated gene regulation may differentially regulate metabolism in ILC vs IDC cells, we identified genes regulated by treatment with 17β-estradiol in our transcriptomic data from ILC models MM134 and MM330 [37], IDC model HCC1428 [37], and consensus ER target genes across breast cancer cell lines ([38], primarily IDC model MCF7). Among shared estrogen-regulated genes, lipid metabolism pathways were strongly enriched (n=83 genes across enriched lipid metabolism-related genesets; Supplemental File 4 ).…”

“…ILC cell lines (n=3; MM134, 44PE, MM330) were in the top 4 lines most sensitive to knockdown of genes in this pathway ( Figure 5F ) and clustered independently from other ER+ lines ( Figure 5G , left). ILC-like cell line CAMA1 [37, 40] was similarly overall sensitive to knockdown of pyruvate production genes ( Figure 5F ). This phenotype was specific for pyruvate production as TCA cycle genes (e.g.…”

A Distinct Chromatin State Drives Therapeutic Resistance in Invasive Lobular Breast Cancer

“…Previous studies identified several mechanisms of tamoxifen resistance unique to ILC models (39,40).…”

A Distinct Chromatin State Drives Therapeutic Resistance in Invasive Lobular Breast Cancer

“…Previous studies identified several mechanisms of tamoxifen resistance unique to ILC models (39,40). We have now unraveled a novel mechanism of tamoxifen resistance in ILC.…”