Hexose Transport in Normal and in Rous Sarcoma Virus-transformed Cells

Abstract

Transport across the cell membrane of 3-O-methylglucose, a nonphosphorylatable glucose analogue, was measured in cultures of chick embryo fibroblasts which were either growing exponentially, contact-inhibited, or transformed by Rous sarcoma virus. Transport of this hexose was found to be 4 to 5 times faster in transformed cells than in normal cells growing at the same rate, and 30 times faster than in contact-inhibited cells. The rate of efflux was increased to the same extent as the rate of influx. 3-O-Methylglucose transport in these cells was found to be a saturable process which was not accompanied by post-transport phosphorylation and which did not result in accumulation of the hexose against a concentration gradient. It is concluded that a facilitated diffusion system for hexose transport is activated in the transformed cells. Kinetic measurements revealed that the Km for transport of 3-O-methylglucose or of 2-deoxyglucose and the Ki for the phlorizin inhibition of 2-deoxyglucose transport were not significantly altered by malignant transformation. Only the Vmax for hexose uptake showed consistent, significant change. We suggest that a new hexose transport system is not synthesized in the transformed cells and that the activation of hexose transport occurs via either a modification or additional de novo synthesis of the normal cellular transport system.