Submitted on February 21, 2007
Accepted on April 11, 2007
Differential regulation of cyclin D1 and cell death by bile acids in primary rat hepatocytes
Rui E Castro1, Joana D Amaral1, Susana Solá2, Betsy T Kren3, Cliff Steer3, and Cecilia M.P. Rodrigues4*
1 CPM, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal
2 Lisbon, Portugal; CPM, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal
3 Medicine, University of Minnesota, Minneapolis, Minnesota, United States
4 Centro de Patogenese Molecular, University of Lisbon, Lisbon, Portugal
* To whom correspondence should be addressed. E-mail: cmprodrigues{at}ff.ul.pt.
Ursodeoxycholic (UDCA) and tauroursodeoxycholic (TUDCA) acids modulate apoptosis and regulate cell cycle effectors, including cyclin D1. In contrast, deoxycholic acid (DCA) induces cell death and cyclin D1. In this study, we explored the role of cyclin D1 in DCA-induced toxicity and further elucidated the anti-apoptotic function of UDCA and TUDCA in primary rat hepatocytes. Cells were incubated with DCA, ±UDCA or TUDCA for 8-30 h. In addition, hepatocytes were transfected with either an adenovirus expressing cyclin D1 or with a cyclin D1 reporter plasmid, ± bile acids. Finally, cells were co-transfected with siRNA targeting p53. Unlike DCA, both UDCA and TUDCA reduced cyclin D1 expression and transcriptional activation, confirming our previous DNA microarray data. Further, UDCA and TUDCA prevented DCA-induced cyclin D1 and cell death. Cyclin D1 overexpression increased DCA-induced Bax translocation, cytochrome c release and apoptosis. However, UDCA and TUDCA were less efficient at decreasing cyclin D1 levels as well as DCA-induced changes with overexpression. Finally, after p53 silencing, the effects of cyclin D1 overexpression were almost completely abrogated, while UDCA and TUDCA cytoprotective potential was reestablished. In conclusion, Cyclin D1 is a relevant player in modulating apoptosis by bile acids, in part through a p53-dependent mechanism.
