CDK inhibitors, p21Cip1 and p27Kip1, participate in cell cycle exit of mammalian cardiomyocytes

• Published in: Biochemical and biophysical research communications 2014-01, Vol.443 (3), p.1105-1109
• Main Authors: Tane, Shoji, Ikenishi, Aiko, Okayama, Hitomi, Iwamoto, Noriko, Nakayama, Keiichi I., Takeuchi, Takashi
• Format: Article
• Language: English
• Subjects: Cardiomyocyte; CDK inhibitor; Cell cycle exit; Mouse
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2013.12.109

•Expression of p21 and p27 in the hearts showed a peak during postnatal stages.•p21 and p27 bound to cyclin E, cyclin A and CDK2 in the hearts at postnatal stages.•Cardiomyocytes in both KO mice showed failure in the cell cycle exit at G1-phase.•These data show the first apparent phenotypes in the hearts of Cip/Kip KO mice. Mammalian cardiomyocytes actively proliferate during embryonic stages, following which cardiomyocytes exit their cell cycle after birth. The irreversible cell cycle exit inhibits cardiac regeneration by the proliferation of pre-existing cardiomyocytes. Exactly how the cell cycle exit occurs remains largely unknown. Previously, we showed that cyclin E- and cyclin A-CDK activities are inhibited before the CDKs levels decrease in postnatal stages. This result suggests that factors such as CDK inhibitors (CKIs) inhibit CDK activities, and contribute to the cell cycle exit. In the present study, we focused on a Cip/Kip family, which can inhibit cyclin E- and cyclin A-CDK activities. Expression of p21Cip1 and p27Kip1 but not p57Kip2 showed a peak around postnatal day 5, when cyclin E- and cyclin A-CDK activities start to decrease. p21Cip1 and p27Kip1 bound to cyclin E, cyclin A and CDK2 at postnatal stages. Cell cycle distribution patterns of postnatal cardiomyocytes in p21Cip1 and p27Kip1 knockout mice showed failure in the cell cycle exit at G1-phase, and endoreplication. These results indicate that p21Cip1 and p27Kip play important roles in the cell cycle exit of postnatal cardiomyocytes.