Okadaic acid-mediated induction of the c-fos gene in estrogen receptor-negative human breast carcinoma cells utilized, in part, posttranscriptional mechanisms involving adenosine-uridine-rich elements.
Signal transduction via modulation of phosphorylation after selective inhibition of protein phosphatase (PP) 1 and/or PP2A appears to play a role in okadaic acid (OA)-mediated effects. Treatment of several estrogen receptor-negative human breast carcinoma (HBC) cells with 100 nM OA resulted in induction of c-fos, c-myc, and cyclin-dependent kinase inhibitor p21WAF1/CIP1 genes. Transfections of various luciferase reporter constructs in HBC cells revealed involvement of activator protein-1-dependent as well as -independent pathways in induction of the c-fos gene by OA. MDA-MB-468 HBC cells were stably transfected with plasmids expressing luciferase, chimeric luciferase- c-fos 3' untranslated region (3'UTR), or chimeric luciferase-p21WAF1/CIP 3'UTR mRNAs. Expression of chimeric luciferase-c-fos and luciferase-p21WAF1/CIP1 mRNAs was elevated by OA in several independent sublines. Actinomycin D chase experiments revealed an enhanced rate of decay of luciferase-c-fos mRNA, whereas treatment with OA caused approximately 3.5-fold enhanced stability of the chimeric luciferase-c-fos mRNA only. By transfecting different plasmids containing deletions of c-fos 3'UTR, OA-responsive sequences were mapped to an 86-nucleotide, AU-rich region. UV cross-linking experiments using HBC cell cytosolic proteins showed multiple complexes with the AU-rich region subfragments of c-fos, as well as c-myc and p21WAF1/CIP1 mRNAs. OA enhanced binding of a novel Mr approximately 75,000 protein present in the cytosolic extracts of HBC cells to the AU-rich RNA probes of all of the above three genes. Taken together, OA regulation of HBC cell gene expression involves the activator protein-1 pathway, as well as enhanced binding of a novel Mr approximately 75,000 protein to an AU-rich region of the 3'UTRs of the target genes.
Farhana
L
L
Department of Internal Medicine and Karmanos Cancer Institute, Wayne State University, Detroit, Michigan 48201, USA.
Boyanapalli
M
M
Tschang
S H
SH
Sun
R J
RJ
Hsu
C K
CK
Zhang
Y X
YX
Fontana
J A
JA
Rishi
A K
AK
D000241:Adenosine; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D016762:Genes, fos; D016259:Genes, myc; D006801:Humans; D019319:Okadaic Acid / Q000494:pharmacology* / Q000627:therapeutic use; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D011960:Receptors, Estrogen / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D014407:Tumor Cells, Cultured; D014529:Uridine
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D011960:Receptors, Estrogen; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D000241:Adenosine; D014529:Uridine