title: p21Cip1 protection against hyperoxia requires Bcl-XL and is uncoupled from its ability to suppress growth.
abstract: The cyclin-dependent kinase inhibitor p21Cip1/Waf1/Sdi1 protects the lung against hyperoxia, but the mechanism of protection remains unclear because loss of p21 does not lead to aberrant cell proliferation. Because some members of the Bcl-2 gene family have been implicated in hyperoxia-induced cell death, the current study investigated their expression as well as p21-dependent growth suppression and cytoprotection. Conditional overexpression of full-length p21, its amino-terminal cyclin-binding (p211-82NLS) domain or its carboxy-terminal PCNA-binding (p2176-164) domain inhibited growth of human lung adenocarcinoma H1299 cells, but only the full-length protein was cytoprotective. Low levels of p21 inhibited cell proliferation, whereas higher levels were required for protection. Expression of the anti-apoptotic protein Bcl-XL declined during hyperoxia but was maintained in cells expressing p21. RNA interference (RNAi) knockdown of Bcl-XL enhanced hyperoxic death of cells expressing p21, whereas overexpression of Bcl-XL increased cell survival. Consistent with growth suppression and cytoprotection requiring different levels of p21, hyperoxia inhibited PCNA expression in p21+/+ and p21+/- mice but not in p21-/- mice. In contrast, p21 was haplo-insufficient for maintaining expression of Bcl-XL and protection against hyperoxia. Taken together, these data show that p21-mediated cytoprotection against hyperoxia involves regulation of Bcl-XL and is uncoupled from its ability to inhibit proliferation.
authors.affiliation: Department of Environmental Medicine, Box 850, The University of Rochester, 601 Elmwood Ave., Rochester, NY 14642, USA.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Vitiello
authors.forename: Rhonda J
authors.initials: RJ
authors.lastname: Staversky
authors.forename: Sean C
authors.initials: SC
authors.lastname: Gehen
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Johnston
authors.forename: Jacob N
authors.initials: JN
authors.lastname: Finkelstein
authors.forename: Terry W
authors.initials: TW
authors.lastname: Wright
authors.forename: Michael A
authors.initials: MA
authors.lastname: O'Reilly
mesh_terms: D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000502:physiology*; D006801:Humans; D000860:Hypoxia; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D051381:Rats; D051020:bcl-X Protein / Q000378:metabolism*
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D051020:bcl-X Protein