hnRNP A2 and hnRNP L bind the 3 ' UTR of glucose transporter 1 mRNA and exist as a complex in vivo

Recent work identified an RNA binding protein whose presence in brain tumor s correlated with translational repression of Glut1 expression. RNase T1 ma pping demonstrated that this protein bound an AU-rich response element (AUR E) in the Glut1 3'UTR. Facilitated by its differential expression in brain tumor cytosols, we identified this Glut1 RNA binding protein as hnRNP A2. S tudies further demonstrated that hnRNP A2 was the major Glut1 RNA binding a ctivity in other cell lines. Recombinant hnRNP A2 exhibited equivalent Glut 1 RNA binding specificity, quite distinct from the related AURE binding pro tein hnRNP Al. These data indicate that hnRNP A2 is the Glut1 AURE binding protein whose cytoplasmic expression in gliomas is associated with translat ional repression and mRNA instability, Using this approach, we also identif ied the other major Glut1 3'UTR RNA binding activity as hnRNP L. Stimuli (h ypoxia and hypoglycemia) which increase Glut1 mRNA stability selectively de creased polysomal levels of hnRNP A2 and L,. Immunoprecipitation demonstrat ed that hnRNP A2 and L, exist as a complex in vivo. As a result of these an d other studies, we conclude that hnRNP A2 and L associate in vivo and inde pendently bind the 3'UTR of Glut1 mRNA. (C) 1999 Academic Press.