title: Glucose Uptake and Intracellular pH in a Mouse Model of Ductal Carcinoma In situ (DCIS) Suggests Metabolic Heterogeneity.
abstract: Mechanisms for the progression of ductal carcinoma in situ (DCIS) to invasive breast carcinoma remain unclear. Previously we showed that the transition to invasiveness in the mammary intraepithelial neoplastic outgrowth (MINO) model of DCIS does not correlate with its serial acquisition of genetic mutations. We hypothesized instead that progression to invasiveness depends on a change in the microenvironment and that precancer cells might create a more tumor-permissive microenvironment secondary to changes in glucose uptake and metabolism. Immunostaining for glucose transporter 1 (GLUT1) and the hypoxia marker carbonic anhydrase 9 (CAIX) in tumor, normal mammary gland and MINO (precancer) tissue showed differences in expression. The uptake of the fluorescent glucose analog dye, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG), reflected differences in the cellular distributions of glucose uptake in normal mammary epithelial cells (nMEC), MINO, and Met1 cancer cells, with a broad distribution in the MINO population. The intracellular pH (pHi) measured using the fluorescent ratio dye 2',7'-bis(2-carboxyethyl)-5(6)-155 carboxyfluorescein (BCECF) revealed expected differences between normal and cancer cells (low and high, respectively), and a mixed distribution in the MINO cells, with a subset of cells in the MINO having an increased rate of acidification when proton efflux was inhibited. Invasive tumor cells had a more alkaline baseline pHi with high rates of proton production coupled with higher rates of proton export, compared with nMEC. MINO cells displayed considerable variation in baseline pHi that separated into two distinct populations: MINO high and MINO low. MINO high had a noticeably higher mean acidification rate compared with nMEC, but relatively high baseline pHi similar to tumor cells. MINO low cells also had an increased acidification rate compared with nMEC, but with a more acidic pHi similar to nMEC. These findings demonstrate that MINO is heterogeneous with respect to intracellular pH regulation which may be associated with an acidified regional microenvironment. A change in the pH of the microenvironment might contribute to a tumor-permissive or tumor-promoting progression. We are not aware of any previous work showing that a sub-population of cells in in situ precancer exhibits a higher than normal proton production and export rate.
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Lobo
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Neil E
authors.initials: NE
authors.lastname: Hubbard
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Damonte
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Mori
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Zsófia
authors.initials: Z
authors.lastname: Pénzváltó
authors.affiliation: Department of Human Physiology and Membrane Biology, University of California at Davis Davis, CA, USA.
authors.forename: Cindy
authors.initials: C
authors.lastname: Pham
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Koehne
authors.affiliation: Center for Comparative Medicine, University of California at Davis Davis, CA, USA.
authors.forename: Aiza C
authors.initials: AC
authors.lastname: Go
authors.affiliation: Department of Human Physiology and Membrane Biology, University of California at Davis Davis, CA, USA.
authors.forename: Steve E
authors.initials: SE
authors.lastname: Anderson
authors.affiliation: Department of Human Physiology and Membrane Biology, University of California at Davis Davis, CA, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Cala
authors.affiliation: Center for Comparative Medicine, University of California at DavisDavis, CA, USA; Department of Pathology, School of Medicine, University of California at DavisSacramento, CA, USA.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Borowsky
keywords: ductal carcinoma in situ; glucose uptake; intracellular pH; mouse mammary carcinoma model; proton export; tumor heterogeneity; tumor microenvironment