Identification of a novel glucose transporter in medullary thyroid carcinomas and phaeochromocytomas

Abstract

Abstract Background The authors previously reported that medullary thyroid carcinomas (MTCs) and phaeochromocytomas avidly take up the glucose analogue fluorodeoxyglucose (FDG) on FDG positron emission tomography. It was also shown that these tumours do not express any of the known human glucose transporters (Glut 1–5), which are responsible for glucose and FDG uptake into cells. It was hypothesized that a novel glucose transporter is responsible for glucose uptake in MTCs and phaeochromocytomas. Methods Using protein sequences from the known human glucose transporters (Glut 1–5), the National Center for Biotechnical Information expressed sequence tag database was screened for novel homologous sequences. Clones derived were used to screen a pooled kidney complementary DNA (cDNA) library, and cDNAs identified were used to identify patterns of expression by Northern blot analysis. Results A novel member of the human glucose transporter family, called Glut X2, was identified. This transporter had 33 per cent protein sequence identity to Glut 3. Hydropathic analysis showed exofacial and transmembrane domain structure consistent with a hexose transporter. Northern blot analysis showed expression of Glut X2 in all seven MTCs studied, all three phaeochromocytomas and in TT cells, an MTC cell line. These tumours did not express any of the other known facilitative glucose transporters (Glut 1–5). Conclusion A novel member of the human glucose transporter family has been identified which may be responsible for glucose uptake in MTCs and phaeochromocytomas.