title: Altered regulation of PDK4 expression promotes antiestrogen resistance in human breast cancer cells.
abstract: Acquired or de novo resistance to the selective estrogen receptor modulators tamoxifen and fulvestrant (ICI) is a major barrier to successful treatment of breast cancer. Gene expression patterns in tamoxifen resistant (TamR-MCF-7) cells were compared to their parental cells (MCF-7L) to identify an aberrantly regulated metabolic pathway. TamR-MCF-7 cells are cross resistant to ICI and doxorubicin, and have increased mitochondrial DNA. A small subset of genes had altered expression in TamR-MCF-7 relative to MCF-7L cells. One of the genes, pyruvate dehydrogenase kinase-4 (PDK4), phosphorylates pyruvate dehydrogenase (PDH). PDK4 expression was elevated in TamR-MCF-7 cells; this result was also observed in a second model of acquired antiestrogen resistance. PDK4 expression is controlled in part by glucocorticoid response elements in the PDK4 gene promoter. In MCF-7L cells, PDK4 mRNA expression was insensitive to glucocorticoid receptor agonists, while dexamethasone dramatically increased PDK4 expression in TamR-MCF-7 cells. Using siRNA to knock down PDK4 expression increased TamR-MCF-7 sensitivity to ICI; in contrast adapting cells to growth in glucose depleted media did not affect ICI sensitivity. Despite TamR-MCF-7 cells high levels of PDK4 mRNA relative to MCF-7L, TamR-MCF-7 cells have increased PDH activity. Wild type MCF-7 cells are reported to be heterozygous for a G to A mutation that results in a substitution of threonine for alanine near PDK4's catalytic site. We found loss of heterozygosity in TamR-MCF-7 cells; TamR-MCF-7 are homozygous for the wild type allele. These data support a role for altered regulation of PDH by PDK4 and altered substrate utilization in the development of drug resistance in human breast cancer cells.
authors.affiliation: Department of Biomedical Sciences, University of Minnesota Medical School, Duluth Campus, Duluth, MN USA.
authors.forename: William
authors.initials: W
authors.lastname: Walter
authors.affiliation: Department of Biomedical Sciences, University of Minnesota Medical School, Duluth Campus, Duluth, MN USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Thomalla
authors.affiliation: Department of Biomedical Sciences, University of Minnesota Medical School, Duluth Campus, Duluth, MN USA.
authors.forename: Josh
authors.initials: J
authors.lastname: Bruhn
authors.affiliation: Masonic Cancer Center, University of Minnesota, Minneapolis, MN USA.
authors.forename: Dedra H
authors.initials: DH
authors.lastname: Fagan
authors.affiliation: Department of Biomedical Sciences, University of Minnesota Medical School, Duluth Campus, Duluth, MN USA.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Zehowski
authors.affiliation: Masonic Cancer Center, University of Minnesota, Minneapolis, MN USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Yee
authors.affiliation: Department of Biomedical Sciences, University of Minnesota Medical School, Duluth Campus, Duluth, MN USA ; Masonic Cancer Center, University of Minnesota, Minneapolis, MN USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Skildum
keywords: Antiestrogen resistance; Breast cancer; Glucose; Metabolism; Pyruvate dehydrogenase kinase-isoform 4 (PDK4)