Fig. 6
Drawing showing the putative role of PTB in the regulation of insulin mRNA stability. We hypothesize that glucose and hypoxia increase binding of PTB to the pyrimidine-rich sequence in ins-PRS by their ability to increase the redox potential of the β cell. Interaction between PTB and the ins-PRS leads to an increased stability of the mRNA. Because PTB has been shown, in other systems, to participate in both translation and polyadenylation processes, it is possible that PTB might act by forming a loop of the insulin mRNA. Circularization of RNA is known to promote both higher messenger stability, as well as a more efficient translation. So far the hypoxia signaling pathways leading to increase ins-PRS-PTB binding are unknown. Because exogenous addition of hydrogen peroxide (H2O2) decreased the hypoxia-induced ins-PRS-PTB interaction, it is possible that the changes of the redox potential and/or reactive oxygen species mediate the hypoxia- and glucose-induced signals.