Transforming oncogenes regulate glucose transport by increasing transporter affinity for glucose: Contrasting effects of oncogenes and heat stress in a murine marrow-derived cell line

Abstract

Transforming oncogenes often overcome the growth factor requirements of cells by activating growth factor signal transduction pathways. Increased energy utilization by transformed cells is a well known phenomenon, but whether glucose uptake is regulated at the level of the glucose transporter has not been clearly established. To determine whether cell transformation by specific oncogenes like, ν-H- ras and ν- abl affects the activation state of glucose transporters, bone marrow-derived IL-3-dependent 32D (clone3) cells transfected with temperature-sensitive ras and abl oncogenes were used to compare proliferative responses and glucose transporting ability of these cells with the parental cell line at permissive (32 °C) and non-permissive (40 °C) temperatures. Transformed cells showed elevated incorporation of [ 3H]thymidine and enhanced tyrosine kinase activity, both of which were abrogated in temperature-sensitive mutants maintained at the non-permissive temperature. Compared with control cells, 2-deoxy-D-[1- 3H]glucose (2-DOG) uptake was not significantly different in transformed cells at the permissive temperature. However, transformation was associated with a 2–2.5-fold greater affinity of glucose transporters for glucose (K m) and this was reversed following treatment with tyrosine kinase inhibitor, genistein. Maximum velocity of glucose transport (V max) and membrane expression of transporters were reduced in oncogene-transformed cells. At the non-permissive temperature, glucose uptake was elevated in both control and oncogene-transformed cells. This increase in glucose transport was not associated with a change in transporter affinity for glucose, but increased Glut-1 expression was observed indicating a ‘heat stress’ effect that overrode the effects attributable to oncogene loss. The ‘heat stress’ effect was inhibited by protein synthesis inhibitor cycloheximide. These results provide evidence for intrinsic activation of glucose transporters by the transforming oncogenes ras and abl and indicate that oncogenes and ‘heat stress’ regulate glucose transport by different mechanisms.