Phosphorylation of a tropomyosin-like (30 KD) protein during platelet activation

The substrate-associated protein p45 of porcine endothelial cells: multiple isoforms, cytoskeletal-like properties and induction by hyperoxic stress

1. Cultured mesenchymal cells respond to hyperoxic (hyper-O2) stress with increased cell flattening/substrate adhesion and overall 47-69% reductions in total matrix-associated (i.e. saponin-resistant [SAP fraction]) protein. 2. Electrophoretic analysis revealed a selective hyper-O2-related 2.7- to 4-fold increase in SAP and cytoskeletal fraction deposition of the protein p45 beginning early (within 12 hr) after initial exposure of porcine endothelial cells to hyper-O2 and increasing over a 48 hr period. 3. p45 consisted of 8 distinct isoforms differing only in pI; hyper-O2-augmented matrix deposition of 3. p45 consisted of 8 distinct isoforms differing only in pI; hyper-02-augmented matrix deposition of p45 involved all 8 isoforms with the more basic subtypes exhibiting slightly greater net increases. 4. Both the specificity and time course of p45 induction, relative to the onset of hyper-O2 cytoarchitectural remodeling, indicate that p45 up-regulation constitutes an early aspect of the hyper-O2 adaptive response.

Calmodulin-dependent phosphatase preferentially dephosphorylates a 28 kDa protein in human platelets

1. Human platelets contain a calmodulin-dependent phosphatase (calcineurin) that has many properties similar to those of bovine brain calmodulin-dependent phosphatase. 2. The activity of calcineurin phosphatase accounts for a small fraction of the total phosphatase activity in human platelets. 3. Labeling of human platelets with 32P yielded many phosphoproteins. 4. Incubation of a lysate of the 32P-labeled platelets with bovine brain calmodulin-dependent phosphatase led to preferential dephosphorylation of a 28 kDa protein (P28), a minor component of platelet proteins. 5. P28 is one of several proteins that were rapidly labeled upon stimulation of platelets with thrombin. 6. Even though the enzyme is known to catalyze the dephosphorylation of many substrates in vitro, its apparent preference for P28 suggests that its activity is highly selective.

Adrenergic stimulation of lens cytoskeletal phosphorylation

Stimulation of lens fiber cytoskeletal phosphorylation by adrenergic drugs is described. The effect of isoproterenol on phosphorylation of the 47 Kd beaded filament protein is dose-dependent, detectable as soon as one minute after treatment and blocked by propranolol. Epinephrine increases the phosphorylation of both 47 Kd and the intermediate filament protein, vimentin. 47 Kd phosphorylation is also increased by norepinephrine, dibutyryl-cAMP or forskolin. The results indicate that lens fiber cytoskeletal phosphorylation is regulated, at least in part, via a beta-adrenergic receptor coupled to cyclic AMP production.