Mechanisms of dexamethasone-mediated inhibition of cAMP-induced tPA expression in rat mesangial cells.
BACKGROUND
Glucocorticoids are efficiently used as antiinflammatory and immunosuppressive therapies of renal diseases. However, long-term treatment often is associated with net changes in the turnover of extracellular matrix (ECM) components.


METHODS
We examined the impact of glucocorticoids on cAMP-triggered expression of tissue plasminogen activator (tPA), a protease prominently involved in glomerular ECM turnover.


RESULTS
By ELISA, the db-cAMP-mediated increase in extracellular tPA activity secreted by mesangial cells (MC) was markedly reduced in the presence of 100 nmol/L dexamethasone. The decrease of enzymatic activity was accompanied by an attenuation of tPA expression, as shown by Northern blot analysis. Furthermore, dexamethasone increased the steady-state mRNA level of the tPA-inhibitor 1 (PAI-1), thereby providing an additional mode of regulation of tPA activity. Mutational analysis revealed that the inhibition of tPA expression was localized within the proximal 2.3 kb of the 5'-flanking region of the rat tPA gene and critically depended on a cAMP response element (CRE) at position -185. EMSA demonstrated that binding to this CRE was affected by dexamethasone, since the db-cAMP-caused DNA binding of CREB and C/EBPbeta-immunopositive complexes was substantially reduced by dexamethasone. In parallel, dexamethasone decreased the nuclear abundance of db-cAMP-induced C/EBPbeta and phosphorylated CREB protein without affecting the total level of either transcription factor.


CONCLUSIONS
Suppression of cAMP-stimulated tPA expression by glucocorticoids occurs by interference with CREB and C/EBPbeta, the major transcription factors mediating cAMP responses. These observations may provide the molecular basis for the sclerotic processes within the glomerulus often complicating chronic glucocorticoid treatment.
Eberhardt
Wolfgang
W
Pharmazentrum Frankfurt, Klinikum der Johann Wolfgang Goethe-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany. w.eberhardt@em.uni-frankfurt.de
Engels
Christina
C
Müller
Roswitha
R
Pfeilschifter
Josef
J
D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002467:Cell Nucleus / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D005920:Glomerular Mesangium / Q000187:drug effects / Q000502:physiology*; D005938:Glucocorticoids / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011485:Protein Binding / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D010959:Tissue Plasminogen Activator / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
D022782:CCAAT-Enhancer-Binding Protein-beta; D017362:Cyclic AMP Response Element-Binding Protein; D005938:Glucocorticoids; D012333:RNA, Messenger; D003907:Dexamethasone; D000242:Cyclic AMP; D010959:Tissue Plasminogen Activator