Downregulation of JE and KC genes by glucocorticoids does not prevent the G0----G1 transition in BALB/3T3 cells.

Rameh LE, Armelin MC
Mol Cell Biol. 1992 12 (10): 4612-21

PMID: 1406651 · PMCID: PMC360388 · DOI:10.1128/mcb.12.10.4612

The effects of glucocorticoid hormones on the expression of the growth factor-inducible genes JE, KC, and c-myc were analyzed in parental BALB/3T3 and polyomavirus middle-T antigen-transfected cell lines. Northern (RNA) blot hybridization and run-on transcription analysis showed that (i) glucocorticoid hormones selectively inhibit JE and KC expression at the transcriptional level and (ii) the downregulatory effect of glucocorticoids on JE and KC expression is partial for serum-stimulated and middle T antigen-transformed cells and total for quiescent and exponentially growing cells. Gel mobility assays using AP-1 oligonucleotides showed a positive correlation between glucocorticoid downregulating effect and presence of the AP-1 complex. JE and KC downregulation by means of the AP-1 complex may play a role in the actions of glucocorticoids as anti-inflammatory and antitumor agents. The ability of glucocorticoids to downregulate JE and KC was used to investigate the relevance of these genes to the mitogenic response to serum growth factors. Hydrocortisone did not alter the basal DNA synthesis level displayed by quiescent 3T3 cells, but it potentiated both the mitogenic effect of platelet-derived growth factor and c-myc induction by serum growth factors. Upon serum restimulation, untreated and dexamethasone-treated quiescent 3T3 cultures entered the S phase after an identical time lag (G1). These results suggest that (i) JE and KC are not necessary for the G0----G1----S transition and (ii) c-myc overexpression is likely to be the basis for the potentiating effect of glucocorticoids on serum growth factors.

MeSH Terms (24)

3T3 Cells Animals Antigens, Polyomavirus Transforming Base Sequence Blotting, Northern Chemokine CCL2 Chemokine CXCL1 Chemokines Chemokines, CXC Chemotactic Factors Cycloheximide Cytokines Dexamethasone DNA Down-Regulation G1 Phase Gene Expression Regulation Glucocorticoids Hydrocortisone Kinetics Mice Molecular Sequence Data Proto-Oncogene Proteins c-jun Resting Phase, Cell Cycle

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