ABSTRACT
Hyperthermal stress and resulting free radical generation is known to impair endurance capacity and immune cell redistribution during prolonged exercise. Caffeic acid phenethyl ester (CAPE), a phenolic compound purified from propolis, has many biological and pharmacological activities including antioxidation. To examine whether CAPE has protective effect against hyperthermal stress in athletes, we isolated peripheral blood mononuclear cells (MNC) from competitive cyclists and assessed their response to hyperthermia with or without CAPE pretreatment. We found that pretreatment of cyclists' MNC with CAPE (0, 1, 2, 4 microg/mL) reversed or reduced hyperthermia-induced survival inhibition, necrosis, superoxide production, glutathione depletion, and intracellular superoxide burst in a dose-dependent manner. These results suggest that CAPE may enhance the hyperthermal tolerance in immune mononuclear cells of competitive cyclists.
Subject(s)
Antioxidants/pharmacology , Caffeic Acids/pharmacology , Hot Temperature/adverse effects , Leukocytes, Mononuclear/drug effects , Phenylethyl Alcohol/analogs & derivatives , Physical Fitness/physiology , Stress, Physiological/drug effects , Bicycling , Cell Survival/drug effects , Cells, Cultured , Dose-Response Relationship, Drug , Exercise Test , Glutathione/analysis , Humans , In Vitro Techniques , Leukocytes, Mononuclear/pathology , Male , Necrosis/prevention & control , Phenylethyl Alcohol/pharmacology , Propolis/chemistry , Superoxides/analysisABSTRACT
TRIP-Br proteins are a novel family of transcriptional coregulators involved in E2F-mediated cell cycle progression. Three of the four mammalian members of TRIP-Br family, including TRIP-Br1, are known oncogenes. We now report the identification of the Balpha regulatory subunit of serine/threonine protein phosphatase 2A (PP2A) as a novel TRIP-Br1 interactor, based on an affinity binding assay coupled with mass spectrometry. A GST-TRIP-Br1 fusion protein associates with catalytically active PP2A-ABalphaC holoenzyme in vitro. Coimmunoprecipitation confirms this association in vivo. Immunofluorescence staining with a monoclonal antibody against TRIP-Br1 reveals that endogenous TRIP-Br1 and PP2A-Balpha colocalize mainly in the cytoplasm. Consistently, immunoprecipitation followed by immunodetection with anti-phosphoserine antibody suggest that TRIP-Br1 exists in a serine-phosphorylated form. Inhibition of PP2A activity by okadaic acid or transcriptional silencing of the PP2A catalytic subunit by small interfering RNA results in downregulation of total TRIP-Br1 protein levels but upregulation of serine-phosphorylated TRIP-Br1. Overexpression of PP2A catalytic subunit increases TRIP-Br1 protein levels and TRIP-Br1 co-activated E2F1/DP1 transcription. Our data support a model in which association between PP2A-ABalphaC holoenzyme and TRIP-Br1 in vivo in mammalian cells represents a novel mechanism for regulating the level of TRIP-Br1 protooncoprotein.
