Orthovanadate Stimulates Cyclic Guanosine Monophosphate-Inhibited Cyclic Adenosine Monophosphate Phosphodiesterase Activity in Isolated Rat Fat Pads through Activation of Particulate Myelin Basic Protein Kinase by Protein Tyrosine Kinase

Abstract

Involvement of protein kinases in the stimulation of cGMP-inhibited cAMP phosphodiesterase (PDE) activity by orthovanadate (vanadate) was studied. When the fat pads were incubated with 2 mM vanadate or 10 nM insulin, the stimulation of myelin basic protein kinase (MBPK) activity in the particulate by vanadate reached a maximum at 60 min. In contrast, insulin showed a transient increase at 20 min. A 60-min incubation of the fat pads with vanadate stimulated all activities of protein tyrosine kinase (PTK), MBPK, and PDE in the particulate, in a similar dose-dependent manner. Amiloride, a PTK inhibitor, inhibited the stimulations of three enzymes by vanadate in a similar concentration range. Enzyme fractions, which were separated from the solubilized particulate, were subjected to the immunoblot analysis. A fraction of MBPK was identified to contain a major protein of mol wt (44K) and a minor one (42K), both of which are immunoreactive with a mitogen-activated protein kinase (MAPK) antibody. The partially purified PDE activity was stimulated by the addition of the partially purified MBPK. The further stimulation was observed with the PTK-activated MBPK. These results suggest that vanadate stimulates in part the PDE activity through the activation of the particulate MBPK, probably MAPKs, by PTK sensitive to vanadate.

Orthovanadate Stimulates cAMP Phosphodiesterase 3 Activity in Isolated Rat Hepatocytes through Mitogen-Activated Protein Kinase Activation Dependent on cAMP-Dependent Protein Kinase

“…19,24) The 5Ј-[ Protein Kinase Assays The cytosolic fraction which had been separated from cells treated with insulin or vanadate was used for protein kinase assays. The MAPK activity was determined using a p42/p44 MAP kinase enzyme assay system, according to the manufacturer's instructions (Amersham Pharmacia Biotech).…”

“…[20][21][22] We previously reported that vanadate stimulated the particulate PDE 3 activity of rat fat pads through the activation of myelin basic protein kinase. 23,24) The dense vesicle and peripheral plasma membrane PDEs from hepatocytes have been reported to be hormone-sensitive enzymes. 25,26) The insulin-induced activations of these two PDEs were thought to be achieved by distinct routes.…”

Mechanisms of inhibition of lipolysis by insulin, vanadate and peroxovanadate in rat adipocytes

“…Ueki et al [35] showed that vanadate activates PDE3 in rat fat pads. We found that vanadate and pV induced PDE3B phosphorylation and PDE3B activation to the same extent as 1 nM insulin.…”

Effect of Orthovanadate on Platelet Aggregation Induced by Platelet-Activating Factor

“…These actions include the stimulation of glucose uptake, 3) the activation of glycogen synthase, 4) the inhibition of lipolysis, 5) the stimulation of cAMP phosphodiesterase (PDE), 6,7) and an increase in lipoprotein lipase activity. 8) A further interesting effect was reported by Heyliger et al that oral administration of vanadate to streptozotocin-induced diabetic rats resulted in lowered blood glucose concentrations without a change in insulin concentrations.…”