FIG. 1.

HuR selectively inhibits c-fos ARE-mediated and not other ARE-mediated mRNA decay. RNA blots showing decay of BBB+ARE mRNAs representing class I AREs (fos ARE, myc ARE, and GM3 ARE) and class II AREs (GM-CSF ARE and IL-3 ARE) in NIH 3T3 B₂A₂ cells expressing the control vector (−HuR, upper blots) or wild-type HuR (+HuR, lower blots). NIH 3T3 B₂A₂ cells were transiently cotransfected with one of the test BBB+ARE plasmids, as indicated above each blot, a control plasmid (pSVα-1/GAPDH), and either pTet-Myc-HuR or a control vector, as indicated under each blot. Total cytoplasmic mRNA was isolated at various times after serum stimulation of quiescent cells and analyzed by Northern blot analysis. Transcription of various BBB+ARE mRNAs was driven by the serum-inducible c-fos promoter. The control mRNA (α-globin/GAPDH) was expressed constitutively and served as an internal standard. The times given at the top of each blot correspond to hours after serum induction (S.I.). Nonpolyadenylated [poly(A)⁻] RNA was prepared in vitro by treating RNA samples from the 1-h time point with oligo(dT) and RNase H. Open rectangles and oval symbols depict AREs and AUUUA motifs, respectively.