title: Transcriptional activation of p21(waf1/cip1) by alkylphospholipids: role of the mitogen-activated protein kinase pathway in the transactivation of the human p21(waf1/cip1) promoter by Sp1.
abstract: Alkylphospholipids (ALKs) are a novel class of antitumor agents with an unknown mechanism of action. The first ALK tested in the clinic, miltefosine, has been approved recently in Europe for the local treatment of patients with cutaneous metastasis. Perifosine, the only available oral ALK, is being studied currently in human cancer clinical trials. We have shown previously that perifosine induces p21(waf1/cip1) in a p53-independent fashion and that induction of p21(waf1/cip1) is required for the perifosine-induced cell cycle arrest because cell lines lacking p21(waf1/cip1) are refractory to perifosine. In this report, we investigated the mechanism by which perifosine induces p21(waf1/cip1) protein expression. We observed that perifosine induces the accumulation of p21(waf1/cip1) mRNA without affecting p21(waf1/cip1) mRNA stability. Using several p21(waf1/cip1) promoter-driven luciferase reporter plasmids, we observed that perifosine activates the 2.4-kb full-length p21(waf1/cip1) promoter as well as a p21 promoter construct lacking p53-binding sites, suggesting that perifosine activates the p21(waf1/cip1) promoter independent of p53. The minimal p21 promoter region required for perifosine-induced p21 promoter activation contains four consensus Sp1-binding sites. Mutations in each particular Sp1 site block perifosine-induced p21(waf1/cip1) expression. Moreover, we showed that perifosine activates the mitogen-activated protein/extracellular signal-regulated kinase pathway, and this activation promotes the phosphorylation of Sp1 in known mitogen-activated protein kinase residues (threonine 453 and 739), thereby leading to increased Sp1 binding and enhanced p21(waf1/cip1) transcription. These results represent a novel mechanism by which alkylphospholipids modulate transcription, and may contribute to the discovery of new signal transduction pathways crucial for normal and neoplastic cell cycle control.
authors.affiliation: Molecular Therapeutics Unit, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, Maryland 20892, USA.
authors.forename: Adriana
authors.initials: A
authors.lastname: De Siervi
authors.forename: Maria
authors.initials: M
authors.lastname: Marinissen
authors.forename: Jessica
authors.initials: J
authors.lastname: Diggs
authors.forename: Xiao-Fan
authors.initials: XF
authors.lastname: Wang
authors.forename: Gilles
authors.initials: G
authors.lastname: Pages
authors.forename: Adrian
authors.initials: A
authors.lastname: Senderowicz
mesh_terms: D000478:Alkylation; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D015603:Keratinocytes; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016296:Mutagenesis; D010743:Phospholipids / Q000494:pharmacology*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects* / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D010743:Phospholipids; D016329:Sp1 Transcription Factor; D010767:Phosphorylcholine; C105905:perifosine; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases