The biphasic induction of p21 and p27 in breast cancer cells by modulators of cAMP is posttranscriptionally regulated and independent of the PKA pathway.
Cyclic AMP (cAMP) elevation affects growth arrest and differentiation in a wide variety of breast cell lines; however, the mechanisms associated with this process are poorly understood. Previous studies linked cAMP-mediated growth arrest in breast tumor cells to increased levels of cyclin kinase inhibitor (CKI), p21. In the present study we examined the role of cAMP-dependent protein kinase (PKA) on p21 and p27 induction in the breast cancer cell line, MDA-MB-157. The induction of the CKIs by modulators of cAMP such as cholera toxin (CT) + 1-isobutyl-3-methylxanthine (IBMX) and lovastatin fluctuates with biphasic kinetics (although the kinetics of CKI induction with CT + IBMX treatment are different from that of lovastatin) and is depicted by the periodic accumulation of lower molecular weight forms of p21 and p27 which also correlate with fluctuations in CDK2 activity. Using three different approaches we show that the cAMP-mediated induction of CKIs is independent of PKA activity. In the first approach we treated MDA-MB-157 cells with a variety of cAMP modulators such as CT + IBMX, and forskolin in the presence or absence of H-89, a potent PKA inhibitor. This analysis revealed that the cAMP activators were capable of inducing p21 even though PKA activity was completely eliminated. In the second approach PKA dominant negative stable clones of MDA-MB-157 treated with CT + IBMX or forskolin also resulted in p21 induction, in the absence of any PKA activity. Last, treatment of MDA-MB-157 cells with lovastatin, another known cAMP modulator which also causes growth arrest, resulted in the induction of p21 and p27 without any increase in PKA activity. Collectively, the above results suggest that the induction of p21 by cAMP is through a novel pathway, independent of PKA activity.
Rao
S
S
Division of Molecular Medicine, Wadsworth Center, Laboratory of Diagnostic Oncology, Albany, New York 12201-0509, USA.
Gray-Bablin
J
J
Herliczek
T W
TW
Keyomarsi
K
K
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D008148:Lovastatin / Q000494:pharmacology; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis* / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D013449:Sulfonamides; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D007546:Isoquinolines; D008869:Microtubule-Associated Proteins; D013449:Sulfonamides; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D005576:Colforsin; D002772:Cholera Toxin; D008148:Lovastatin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D018844:Cyclin-Dependent Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D015056:1-Methyl-3-isobutylxanthine