title: Regulation and role of p21 and p27 cyclin-dependent kinase inhibitors during hepatocyte differentiation and growth.
abstract: Unlike a large number of cell types that undergo terminal differentiation associated with permanent withdrawal from the cell cycle, mature quiescent hepatocytes retain high proliferative potential. We report here a specific behavior of members of the Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors during development of the rat liver and proliferation of normal hepatocytes. Expression of p21, p27, and p57 transcripts and proteins was downregulated during the differentiation process to low or undetectable levels in adult liver. In contrast to p27, p21 protein increased in a mitogen-dependent manner in isolated hepatocytes and its expression pattern correlated with that of cyclin D1. In proliferating hepatocytes, p21 was predominantly associated with cyclin D1, these proteins were colocalized in the nucleus and p21-associated retinoblastoma protein (pRb) kinase activity increased in parallel with that of cyclin D1. Overexpression of p21 in mitogen-stimulated hepatocytes reduced DNA synthesis. In contrast, inhibition of p21 expression by antisense or small interfering RNAs oligonucleotides accelerated S phase entry. Finally, expression of p21 and cyclin D1, but not p27 proteins was regulated by MAPK kinase/extracellular signal-regulated kinase and phosphatidylinositol 3-kinase-ferric-reducing ability power/mammalian target of rapamycin signal transduction pathways. In conclusion, these results demonstrate a specific and differential regulation of p21 and p27 during hepatocyte differentiation and proliferation that may contribute to the control of quiescent differentiated hepatic cell proliferating activity.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U522, Avenue de la Bataille Flandre/Dunkerque, Hôpital Pontchaillou, 35033 Rennes Cedex, France. Guennadi.Iline@rennes.inserm.fr
authors.forename: Gennady P
authors.initials: GP
authors.lastname: Ilyin
authors.forename: Denise
authors.initials: D
authors.lastname: Glaise
authors.forename: David
authors.initials: D
authors.lastname: Gilot
authors.forename: Georges
authors.initials: G
authors.lastname: Baffet
authors.forename: Christiane
authors.initials: C
authors.lastname: Guguen-Guillouzo
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D019925:Cyclin A / Q000378:metabolism; D019938:Cyclin D1 / Q000235:genetics; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000235:genetics* / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D022781:Hepatocytes / Q000166:cytology* / Q000201:enzymology; D008297:Male; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D011247:Pregnancy; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016196:S Phase / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: C493958:Cdkn1a protein, rat; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004815:Epidermal Growth Factor; C495903:Cdk4 protein, rat; C495913:Cdk6 protein, rat; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases