An RNA Interference Screen Identifies Metabolic Regulators NR1D1 and PBP as Novel Survival Factors for Breast Cancer Cells with the ERBB2 Signature

Abstract

Overexpression of the adverse prognostic marker ERBB2 occurs in 30% of breast cancers; however, therapies targeting this gene have not proved to be as effective as was initially hoped. Transcriptional profiling meta-analyses have shown that there are ∼150 genes co-overexpressed with ERBB2, suggesting that these genes may represent alternative factors influencing ERBB2-positive tumors. Here we describe an RNA interference-based analysis of these genes that identifies transcriptional regulators of fat synthesis and storage as being critical for the survival of these cells. These transcription factors, nuclear receptor subfamily 1, group D, member 1 (NR1D1) and peroxisome proliferator activated receptor γ binding protein (PBP), both reside on ERBB2-containing 17q12-21 amplicons and are part of the ERBB2 expression signature. We show that NR1D1 and PBP act through a common pathway in upregulating several genes in the de novo fatty acid synthesis network, which is highly active in ERBB2-positive breast cancer cells. Malate dehydrogenase 1 and malic enzyme 1, enzymes that link glycolysis and fatty acid synthesis, are also regulated by NR1D1. The resulting high-level fat production from increased expression of these genes likely contributes to an abnormal cellular energy metabolism based on aerobic glycolysis. Together, these results show that the cells of this aggressive form of breast cancer are genetically preprogrammed to depend on NR1D1 and PBP for the energy production necessary for survival.

Dropping in on the lipid droplet- tumor protein D52 (TPD52) as a new regulator and resident protein

“…22 Like Kourtidis et al, 21 we noted that TPD52 knock-down decreased the survival of ERBB2-positive breast cancer cell lines, 22 which were characterized by higher levels of LD staining. 21 Breast and prostate cancers have been shown to accumulate cytoplasmic LDs, [23][24][25] and ERBB2 expression in breast cancer has been associated with a transcriptional program upregulating fatty acid synthase. 26 TPD52 also has a long history of being identified and studied as an androgen-induced gene/ protein, 27,28 and androgen treatment of prostate cancer cells increases cytoplasmic LDs 25 and regulates key anabolic enzymes.…”

“…Our group reconsidered these and other results following the publication of Kourtidis et al in 2010, which described the reliance of ERBB2-positive breast cancer cell lines upon chromosome 17-encoded regulators of lipid metabolism. 21 At the time, we were analyzing the effects of TPD52 knock-down in breast cell lines. 22 Like Kourtidis et al, 21 we noted that TPD52 knock-down decreased the survival of ERBB2-positive breast cancer cell lines, 22 which were characterized by higher levels of LD staining.…”

“…21 At the time, we were analyzing the effects of TPD52 knock-down in breast cell lines. 22 Like Kourtidis et al, 21 we noted that TPD52 knock-down decreased the survival of ERBB2-positive breast cancer cell lines, 22 which were characterized by higher levels of LD staining. 21 Breast and prostate cancers have been shown to accumulate cytoplasmic LDs, [23][24][25] and ERBB2 expression in breast cancer has been associated with a transcriptional program upregulating fatty acid synthase.…”

“…10 There is therefore no shortage of explanations for why cancer cells might benefit from TPD52 overexpression, but these explanations are relatively generic and would not be expected to favor one cancer cell type over others. Where knock-down studies have been conducted in different breast cell lines, reduced TPD52 expression commonly reduced the survival of ERBB2-positive breast cancer cell lines, 21,22 suggesting a particular function in this cell type. ERBB2-positive breast cancer cell lines are characterized by increased LDs, 21 and ERBB2-positive breast cancers more frequently express proteins associated with lipogenesis or lipid storage.…”

“…Where knock-down studies have been conducted in different breast cell lines, reduced TPD52 expression commonly reduced the survival of ERBB2-positive breast cancer cell lines, 21,22 suggesting a particular function in this cell type. ERBB2-positive breast cancer cell lines are characterized by increased LDs, 21 and ERBB2-positive breast cancers more frequently express proteins associated with lipogenesis or lipid storage. 48 Increased TPD52 expression could therefore favor the survival of cell lines with increased lipogenic activity by contributing to the increased lipid storage capacity that these cells require.…”