Targeting of GLUT6 (formerly GLUT9) and GLUT8 in rat adipose cells

The subcellular targeting of the two recently cloned novel mammalian glucos e transporters, GLUT6 {previously referred to as GLUT9 [Doege, Bocianski, J oost and Schurmann (2000) Biochem. J. 350, 771-776]} and GLUTS, was analyse d by expression of haemagglutinin (HA)-epitope-tagged GLUTs in transiently transfected primary rat adipose cells. Similar to HA-GLUT4, both transporte rs, HA-GLUT6 and HA-GLUT8, were retained in intracellular compartments in n on-stimulated cells. In contrast, mutation of the N-terminal dileucine moti fs in both constructs led to constitutive expression of the proteins on the plasma membrane. Likewise, when endocytosis was blocked by co-expression o f a dominant-negative mutant of the dynamin GTPase, wild-type HA-GLUT6 and HA-GLUT8 accumulated on the cell surface. However, in contrast with HA-GLUT 4, no translocation of HA-GLUT6 and HA-GLUT8 to the plasma membrane was obs erved when the cells were stimulated with insulin, phorbol ester or hyperos molarity. Thus GLUT6 and GLUTS appear to recycle in a dynamin-dependent man ner between internal membranes and the plasma membrane in rat adipose cells , but are unresponsive to stimuli that induce translocation of GLUT4.