Stress-induced inhibition of protein synthesis initiation : Modulation of initiation factor 2 and guanine nucleotide exchange factor activities following transient cerebral ischemia in the rat

• Neuronal protein synthesis is severely depressed following stress such as heat-shock, hypoxia, and hypoglycemia. Following reversible cerebral ischemia, protein synthesis is transiently inhibited in ischemia-resistant areas, but persistently depressed in vulnerable brain regions. Eukaryotic initiation factor 2 (elF-2) activity, that is, the formation of the ternary complex elF-2 · GTP · initiator 35S-Met-tRNA, a rate-limiting step in the initiation of cellular protein synthesis, was studied in the rat brain during and following 15 min of transient global cerebral ischemia. At 30 min and 1 hr of reperfusion, a general decrease of elF-2 activity by approximately 50% was seen in the postmitochondrial supernatant (PMS). In the relatively resistant neocortex and CA3 region of the hippocampus, the elF-2 activity returns to control levels at 6 hr of reperfusion, but remains depressed in the vulnerable striatum and the CA1 region. Similarly, the activity of the guanine nucleotide exchange factor (GEF), which catalyzes the exchange of GTP for GDP bound to elF-2, a crucial step for the continued formation of the ternary complex, is transiently reduced in neocortex but persistently depressed in striatum. The postischemic decrease in elF-2 activity is further attenuated by agarose-bound alkaline phosphatase, and mixing experiments revealed that a vanadate-sensitive phosphatase may be responsible for the depression. Addition of partially purified GEF to PMS from postischemic neocortex restored elF-2 activity to control levels. We conclude that ischemia alters the balance between phosphorylation and dephosphorylation reactions, leading to an inhibition of GEF and a depression of ternary complex formation. The persistent inhibition of GEF and ternary complex formation in areas vulnerable to ischemia may be due to factors causing cell death.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Neurovetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Neurosciences (hsv//eng)

Nyckelord

guanine exchange factor

initiation factor 2

ischemia

neuronal death

phosphatase

phosphorylation

protein synthesis

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art (ämneskategori)

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