Autoantibodies in recent onset type-1 diabetic patients to a Mr 60K microsomal hepatic protein: new evidence for autoantibodies to the type-2 glucose transporter.

Here we describe the presence of IgG antibodies, in the sera of patients presenting with insulin-dependent diabetes mellitus (IDDM), that react in Western blots with a 60-kD protein (Mr 60K) from rat hepatic microsomal extracts. Sera from 60 IDDM patients were screened and 31.6% were positive for the Mr 60K band. This antibody reactivity was indistinguishable in terms of both molecular weight and isoelectric point (pI 5.4) from that described in some patients presenting with autoimmune hepatitis who may also develop IDDM. We hypothesized that the type-2 glucose transporter (Glut-2) that is expressed on both hepatocytes and pancreatic beta cells could be a putative target for the detected antibodies. A polyclonal antisera to rat Glut-2 used in the liver microsome Western blot identified a 60-kD band superimposable upon that evidenced by IDDM sera. Antisera to Glut-2 successfully inhibited the binding of the patient's IgGs to liver microsomes, further suggesting that the two proteins may be identical. Using protein extracts from a rat insulinoma cell line (RIN) transfected with the human Glut-2 cDNA, further evidence was obtained suggesting that these IDDM IgGs are specific for the human Glut-2 transporter.