title: Dexamethasone modulates ErbB tyrosine kinase expression and signaling through multiple and redundant mechanisms in cultured rat hepatocytes.
abstract: Glucocorticoids paradoxically exert both stimulatory and inhibitory effects on the proliferation of cultured rat hepatocytes. We studied the effects of dexamethasone, a synthetic glucocorticoid, on the proliferation of cultured rat hepatocytes. The timing of growth factor addition modified the action of high-dose dexamethasone (10(-6) M) on DNA synthesis. When we added transforming growth factor-alpha at the time of plating, 10(-6) M dexamethasone weakly stimulated DNA synthesis by 26% relative to cells cultured in dexamethasone-free media. When we delayed growth factor addition until 24-48 h after plating, 10(-6) M dexamethasone inhibited DNA synthesis by 50%. Using immunological methods, we analyzed the expression and signaling patterns of the ErbB kinases in dexamethasone-treated cells. High-dose dexamethasone stabilized the expression of epidermal growth factor receptor (EGFr) and ErbB3, and it suppressed the de novo expression of ErbB2 that occurs during the third and fourth day of culture in 10(-8) M dexamethasone. High-dose dexamethasone by 72 h suppressed basal and EGF-associated phosphorylation of ERK and Akt. The reduction in ERK1/2 phosphorylation correlated with suppression of a culture-dependent increase in Son-of sevenless 1 (Sos1) and ERK1/2 expression. High-dose dexamethasone in hepatocytes stabilized or upregulated several inhibitory effectors of EGFr/ErbB2 and ERK, including receptor-associated late transducer (RALT) and MKP-1, respectively. Thus 10(-6) M dexamethasone exerts a time-dependent and redundant inhibitory effect on EGFr-mediated proliferative signaling in hepatocytes, targeting not only the ErbB proteins but also their various positive and negative effectors.
authors.affiliation: Division of Pediatric Endocrinology, 1055 Medical Research Bldg. 4, Vanderbilt University Medical Center, Nashville, TN 37232-0710, USA. lawrence.a.scheving@vanderbilt.edu
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Scheving
authors.forename: Renee
authors.initials: R
authors.lastname: Buchanan
authors.forename: Michael A
authors.initials: MA
authors.lastname: Krause
authors.forename: Xiuqi
authors.initials: X
authors.lastname: Zhang
authors.forename: Mary C
authors.initials: MC
authors.lastname: Stevenson
authors.forename: William E
authors.initials: WE
authors.lastname: Russell
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D054638:Dual Specificity Phosphatase 1; D066246:ErbB Receptors / Q000378:metabolism*; D005938:Glucocorticoids / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000378:metabolism; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D020837:SOS1 Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D016211:Transforming Growth Factor alpha / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D003907:Dexamethasone; D054638:Dual Specificity Phosphatase 1; D066246:ErbB Receptors; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D020837:SOS1 Protein; D016211:Transforming Growth Factor alpha; C517021:Dusp1 protein, rat