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.