The potential mechanism of the diabetogenic action of streptozotocin: inhibition of pancreatic beta-cell O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase.
Streptozotocin (STZ), an analogue of GlcNAc, inhibits purified rat spleen O-GlcNAc-selective N-acetyl-beta-D-glucosaminidase (O-GlcNAcase), the enzyme that removes O-GlcNAc from protein. We have shown previously that STZ increases pancreatic islet O-linked protein glycosylation. In light of these data, we investigated the possibility further that STZ causes beta-cell death by inhibiting O-GlcNAcase. In isolated islets, the time course and dose curve of STZ-induced O-glycosylation correlated with beta-cell toxicity. STZ inhibition of rat islet O-GlcNAcase activity also paralleled that of its beta-cell toxicity, with significant inhibition occurring at a concentration of 1 mM. In contrast, STZ inhibition of rat brain O-GlcNAcase and beta-TC3 insulinoma cell O-GlcNAcase was significantly right-shifted compared with islets, with STZ only significantly inhibiting activity at a concentration of 5 mM, the same concentration required for beta-TC3 cell toxicity. In comparison, N-methyl-N-nitrosourea, the nitric oxide-donating portion of STZ, did not cause increased islet O-glycosylation, beta-cell toxicity or inhibition of beta-cell O-GlcNAcase. Enhanced STZ sensitivity of islet O-GlcNAcase compared with O-GlcNAcase from other tissues or an insulinoma cell line suggests why actual islet beta-cells are particularly sensitive to STZ. Confirming this idea, STZ-induced islet beta-cell toxicity was completely blocked by GlcNAc, which also prevented STZ-induced O-GlcNAcase inhibition, but was not even partially blocked by glucose, glucosamine or GalNAc. Together, these data demonstrate that STZ's inhibition of beta-cell O-GlcNAcase is the mechanism that accounts for its diabetogenic toxicity.
Konrad
R J
RJ
Department of Pathology, University of Alabama at Birmingham, P230G West Pavilion, 619 South 19th Street, Birmingham, AL 35233-7331, USA. rkonrad@path.uab.edu
Mikolaenko
I
I
Tolar
J F
JF
Liu
K
K
Kudlow
J E
JE
D000117:Acetylglucosamine / Q000031:analogs & derivatives*; D000118:Acetylglucosaminidase / Q000037:antagonists & inhibitors*; D000818:Animals; D001921:Brain / Q000201:enzymology; D003921:Diabetes Mellitus, Experimental / Q000209:etiology*; D004305:Dose-Response Relationship, Drug; D006031:Glycosylation / Q000187:drug effects; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin / Q000633:toxicity*
D013311:Streptozocin; D000118:Acetylglucosaminidase; D000117:Acetylglucosamine