Regulation of Nutrient Transport in Quiescent, Lactating, and Neoplastic Mammary Epithelia

The specific aims of this proposal are to characterize the role of GLUT1 and other potential glucose transporters in lactating and neoplastic mammary epithelia, to identify novel transporters or sorters, to describe their developmental regulation, and to test possible associations between glucose transport and the neoplastic phenotype. Double-label immunofluorescence and subcellular fractionation by density gradient centrifugation independently demonstrate that GLUT1 is localized in the Golgi in response to the hormonal milieu of lactation, both in vitro and in vivo; corresponding with this, lactose biosynthesis is increased several-fold. Northern and Western blots for GLUT1 and GLUT5 indicate that the developmental regulation of glucose transporters is isoform-specific, and a precipitous decline in GLUT1 levels at weaning appears not to be due to transcriptional effects, but to changes in translational efficiency or GLUT1 protein degradation. Differential display analysis has shown six genes differentially expressed in mammary epithelial cells treated with prolactin and dexamethasone. One of these is lactate dehydrogenase A, and five are novel, and represent potential candidates to explain the Golgi sequestration of GLUT1 observed in secretion medium. The ability to understand and alter the amount of subcellular targeting of GLUT1 may have therapeutic implications in breast cancer. Original contains color plates: All DTIC reproductions will be in black and white.