Figure 2.

In vitro and in vivo localization of phosphorylation-dependent proteasomal-targeting motif in CREB. (A) Homologous serine phosphorylation sites within IκB, β-catenin, and CREB may represent phosphorylation-dependent targeting sites to ubiquitination and proteasomal degradation (15). (B–D) Sequential serine phosphorylation (CREB-pSER), ubiquitination (CREB-Ub), and expression of CREB. (B) Exposure of T84 cells to hypoxia results in the transient serine phosphorylation of CREB, maximal at 4 h. (C_I) Time-dependent CREB ubiquitination with onset at 8 h. (C_II) Multiple ubiquitinated CREB species. (D) CREB is diminished in epithelial cells with a significant decrease observed by 24 h. (E) CREB levels are decreased in mucosal scrapings (epithelial enriched) from mice exposed to hypoxia. Data shown are representative of at least three experiments.