title: Isolation and characterization of an RNA aptamer for the HPV-16 E7 oncoprotein.
abstract: OBJECTIVE
  Cervical cancer is a common neoplastic disease affecting women worldwide. Expression of human papillomavirus type 16 (HPV-16) E6/E7 genes is frequently associated with cervical cancer, representing ideal targets for diagnostic and therapeutic strategies. Aptamers are oligonucleotide ligands capable of binding with high affinity and specificity to relevant markers in therapeutics and disease detection. The aim of the study was to isolate an RNA aptamer specific for the HPV-16 E7 protein.
  
  
  METHODS
  Aptamers were selected from a randomized oligonucleotide library using a modified SELEX method and recombinant HPV-16 E7 protein. Isolated aptamers were cloned and sequenced for in silico analysis. Interaction and electromobility shift assays (EMSA) were performed to establish aptamer specificity and affinity for E7. RNase footprinting and serial deletions of the aptamer and the E7 protein were made to characterize the aptamer-protein complex. Sandwich slot-blot assays were used for K(D) determination.
  
  
  RESULTS
  After several rounds of SELEX, an aptamer (G5α3N.4) exhibited specificity for E7 using cell-free and protein extracts. G5α3N.4 binding yielded a K(D) comparable to aptamers directed to other small targets. Enzymatic and genetic analysis of G5α3N.4 binding showed a secondary structure with two stem-loop domains joined by single-stranded region contacting E7 in a clamp-like manner. The G5α3N.4 aptamer also produced specific complexes in HPV-positive cervical carcinoma cells.
  
  
  CONCLUSIONS
  The affinity and specificity of G5α3N.4 binding domains for the HPV-16 E7 protein may be used for the detection of papillomavirus infection and cervical cancer.
authors.affiliation: Laboratorio de Terapia Génica, Departamento de Genética y Biología Molecular, CINVESTAV, Mexico, D.F., Mexico.
authors.forename: Julia D
authors.initials: JD
authors.lastname: Toscano-Garibay
authors.forename: María L
authors.initials: ML
authors.lastname: Benítez-Hess
authors.forename: Luis M
authors.initials: LM
authors.lastname: Alvarez-Salas
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry / Q000302:isolation & purification*; D001483:Base Sequence; D002457:Cell Extracts / Q000737:chemistry; D002478:Cells, Cultured; D005260:Female; D052162:Human papillomavirus 16; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009710:Nucleotide Mapping; D050725:Papillomavirus E7 Proteins / Q000737:chemistry*; D011485:Protein Binding; D052156:SELEX Aptamer Technique; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis / Q000821:virology*
chemical_list: D052157:Aptamers, Nucleotide; D002457:Cell Extracts; D050725:Papillomavirus E7 Proteins; C059731:oncogene protein E7, Human papillomavirus type 16