Abstract-The angiotensin type 1 receptor (AT 1 ) exerts a variety of its signaling and cellular actions through its effects on protein phosphorylation. Phosphoproteomic analysis of angiotensin (Ang) II-stimulated aortic smooth muscle cells revealed that heat shock protein 27 (HSP27) represents a major protein phosphorylation target of the AT 1 signaling pathway. Stimulation of cells with Ang II resulted in 1.7-fold (PϽ0.05) and 5.5-fold (PϽ0.001) increases in HSP27 phosphoisoforms at pI 5.7 and pI 5.4, respectively. This was accompanied by a 54% (PϽ0.01) decrease in the nonphosphorylated HSP27 isoform, located at pI 6.4. Treatment of samples with alkaline phosphatase reversed this redistribution of HSP27 phosphoisoforms. Ang II-stimulated HSP27 phosphorylation was completely blocked by pretreatment of cells with the AT 1 antagonist CV11974. Phosphoamino acid analysis demonstrated that Ang II-induced phosphorylation of both HSP27 phosphoisoforms occurred exclusively on serine. Protein kinase C inhibition completely blocked phorbol ester-induced HSP27 phosphorylation but did not impair Ang II-stimulated phosphorylation of HSP27, suggesting that AT 1 increased HSP27 phosphorylation by a protein kinase C-independent pathway. Intrajugular infusion of Ang II in rats increased HSP27 in aorta by 1.7-fold (PϽ0.02), and this response was inhibited by CV11974. These results suggest that Ang II-induced HSP27 phosphorylation is a physiologically relevant AT 1 signaling event. Because serine phosphorylation of HSP27 blocks its ability to cap F-actin, Ang II/AT 1 -induced HSP27 phosphorylation may play a key role in actin filament remodeling required for smooth muscle cell migration and contraction.

Reducing insulin-like growth factor I receptor (IGF-IR) levels or administration of IGF-I show beneficial effects in the brain. We now provide evidence to help resolve this paradox. The unliganded IGF-IR inhibits glucose uptake by astrocytes while its stimulation with IGF-I, in concert with insulin activation of the insulin receptor, produces the opposite effect. In vivo imaging showed that shRNA interference of brain IGF-IR increased glucose uptake by astrocytes while pharmacological blockade of IGF-IR reduced it. Brain 18 FGlucose-PET of IGF-IR shRNA injected mice confirmed an inhibitory role of unliganded IGF-IR on glucose uptake, whereas glucose-dependent recovery of neuronal activity in brain slices was blunted by pharmacological blockade of IGF-IR. Mechanistically, we found that the unliganded IGF-IR retains glucose transporter 1 (GLUT1), the main glucose transporter in astrocytes, inside the cell while IGF-I, in cooperation with insulin, synergistically stimulates MAPK/PKD to promote association of IGF-IR with GLUT 1 via Rac1/GIPC1 and increases GLUT1 availability at the cell membrane. These findings identify IGF-I and its receptor as antagonistic modulators of brain glucose uptake.