title: p16( INK4a) positively regulates cyclin D1 and E2F1 through negative control of AUF1.
abstract: BACKGROUND
  The cyclin-D/CDK4,6/p16(INK4a)/pRB/E2F pathway, a key regulator of the critical G1 to S phase transition of the cell cycle, is universally disrupted in human cancer. However, the precise function of the different members of this pathway and their functional interplay are still not well defined.
  
  
  RESULTS
  We have shown here that the tumor suppressor p16(INK4a) protein positively controls the expression of cyclin D1 and E2F1 in both human and mouse cells. p16(INK4a) stabilizes the mRNAs of the corresponding genes through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by RT-PCR indicated that endogenous AUF1 binds to the cyclin D1 and E2F1 mRNAs. Furthermore, AUF1 down-regulation increased the expression levels of these genes, while concurrent silencing of AUF1 and p16(INK4a), using specific siRNAs, restored normal expression of both cyclinD1 and E2F1. Besides, we have shown the presence of functional AU-rich elements in the E2F1 3'UTR, which contributed to p16/AUF1-mediated regulation of E2F1 post-transcriptional events in vivo. Importantly, genome-wide gene expression microarray analysis revealed the presence of a large number of genes differentially expressed in a p16(INK4a) -dependent manner, and several of these genes are also members of the AUF1 and E2F1 regulons. We also present evidence that E2F1 mediates p16-dependent regulation of several pro- and anti-apoptotic proteins, and the consequent induction of spontaneous as well as doxorubicin-induced apoptosis.
  
  
  CONCLUSIONS
  These findings show that the cyclin-dependent kinase inhibitor p16( INK4a) is also a modulator of transcription and apoptosis through controlling the expression of two major transcription regulators, AUF1 and E2F1.
authors.affiliation: Department of Biological and Medical Research, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.
authors.forename: Huda H
authors.initials: HH
authors.lastname: Al-Khalaf
authors.forename: Dilek
authors.initials: D
authors.lastname: Colak
authors.forename: Maher
authors.initials: M
authors.lastname: Al-Saif
authors.forename: Albandary
authors.initials: A
authors.lastname: Al-Bakheet
authors.forename: Siti-Faujiah
authors.initials: SF
authors.lastname: Hendrayani
authors.forename: Nujoud
authors.initials: N
authors.lastname: Al-Yousef
authors.forename: Namik
authors.initials: N
authors.lastname: Kaya
authors.forename: Khalid S
authors.initials: KS
authors.lastname: Khabar
authors.forename: Abdelilah
authors.initials: A
authors.lastname: Aboussekhra
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001483:Base Sequence; D002460:Cell Line; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000737:chemistry / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D020862:GC Rich Sequence / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D000081035:Heterogeneous Nuclear Ribonucleoprotein D0; D034502:Heterogeneous-Nuclear Ribonucleoprotein D / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C000630986:HNRNPD protein, human; D000081035:Heterogeneous Nuclear Ribonucleoprotein D0; D034502:Heterogeneous-Nuclear Ribonucleoprotein D; C000630987:Hnrpd protein, mouse; D012333:RNA, Messenger; D019938:Cyclin D1; D004317:Doxorubicin