Reactive oxygen species mediate phorbol ester-regulated tyrosine phosphorylation and phospholipase A2 activation: potentiation by vanadate

Abstract

We have previously shown that vanadate potentiates the activating effect of phorbol ester (TPA) on cellular phospholipase A2 (PLA2) in a pathway dependent on the formation of reactive oxygen species (ROS). Here we evaluate the chain of enzymes (protein kinases and phosphatases) that participate in this process. Treatment of macrophages with vanadate plus TPA led to activation of protein kinase C (PKC) and NADPH oxidase (O2- generation in intact cells), massive cellular protein tyrosine phosphorylation, suppression of protein tyrosine phosphatase (PTP) activity and a sustained activation of protein tyrosine kinase (PTK) and myelin basic protein kinase activity (the latter three enzyme activities were assessed in cell lysates). Inhibition of ROS formation by diphenyleneiodonium (DPI) prevented PTP inhibition, PTK activation and protein tyrosine phosphorylation by vanadate plus TPA. Vanadate plus H2O2 mimicked the effect of vanadate plus TPA on PKC activation, cellular protein tyrosine phosphorylation, PTP and PTK, but their effects were resistant to DPI. Suppression of PKC activity (down-regulation; selective inhibitors) prevented the above-mentioned effects of vanadate plus TPA, but not of vanadate plus H2O2. Collectively, the results show that ROS formation induced by TPA in association with vanadate is essential in the modulation of protein tyrosine phosphorylation and PLA2 activity.

Contemporary evidence on the physiological role of reactive oxygen species in human sperm function

“…When phosphatases are downregulated, PLA2 remains activated due to the presence of an attached phosphate group not removed by the weak enzyme [94]. Furthermore, phosphorylation and a subsequent activation of PLA2 may be achieved by a cascade of events involving ROS stimulating PTK, which will act upon PKC, leading to P-PLA2 and sperm membrane degradation [50,95,96] (see Fig. 2).…”

Oxidative Stress Triggers STAT3 Tyrosine Phosphorylation and Nuclear Translocation in Human Lymphocytes

“…Hydrogen Peroxide and Vanadate Act Synergistically to Induce Nuclear Translocation of STAT3-It has been previously proposed that the combination of H 2 O 2 and orthovanadate potently inhibits PTPase activity (25,26) and/or synergistically stimulates insulin-dependent PTK activity (38) in T lymphocytes. Also, the mixture of H 2 O 2 and sodium orthovanadate promotes tyrosine phosphorylation of phospholipase C␥1 and activates p56 lck and p59 fyn tyrosine kinases (23).…”

“…STAT3, a well characterized 92-kDa protein, has been shown to become activated by both epidermal growth factor and interleukin-6 in human A-431 cells (22). Because the ROI generated in response to various external stimuli can play a role both as regulators of transcription factors, including nuclear factors B (2, 23) and AT (24), and as inhibitors of protein-tyrosine phosphatases (PTPases) (25)(26)(27), we have investigated whether H 2 O 2 and other oxidizing agents could modulate STAT3 function in human lymphocytes. Enhanced phosphotyrosine accumulation could then result from the combined effects of increased phosphorylation and decreased dephosphorylation.…”

Hormonally Active Vitamin D3 (1α,25-Dihydroxycholecalciferol) Triggers Autophagy in Human Macrophages That Inhibits HIV-1 Infection

“…IL-1␤-induced tyrosine phosphorylation may be explained by the observation that protein tyrosine phosphorylation can be modulated by intracellular redox potential. Increasing intracellular oxidation can directly enhance protein tyrosine phosphorylation (27)(28)(29) and can also potentiate protein tyrosine phosphorylation induced by other stimuli (30,31). Furthermore, cytokines such as IL-1␤ have been reported to increase oxygen radical release by mesangial cells (32).…”