RESUMEN

Cervical cancer is the fourth most common cause of cancer in women worldwide in terms of both incidence and mortality. Persistent infection with high-risk types of human papillomavirus (HPV), namely 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68, constitute a necessary cause for the development of cervical cancer. Viral oncoproteins E6 and E7 play central roles in the carcinogenic process by virtue of their interactions with cell master proteins such as p53, retinoblastoma (Rb), mammalian target of rapamycin (mTOR), and c-MYC. For the synthesis of E6 and E7, HPVs use a bicistronic messenger RNA (mRNA) that has been studied in cultured cells. Here, we report that in cervical tumors, HPV-18, -39, and -45 transcribe E6/E7 mRNAs with extremely short 5' untranslated regions (UTRs) or even lacking a 5' UTR (i.e., zero to three nucleotides long) to express E6. We show that the translation of HPV-18 E6 cistron is regulated by the motif ACCaugGCGCG(C/A)UUU surrounding the AUG start codon, which we term Translation Initiation of Leaderless mRNAs (TILM). This motif is conserved in all HPV types of the phylogenetically coherent group forming genus alpha, species 7, which infect mucosal epithelia. We further show that the translation of HPV-18 E6 largely relies on the cap structure and eIF4E and eIF4AI, two key translation initiation factors linking translation and cancer but does not involve scanning. Our results support the notion that E6 forms the center of the positive oncogenic feedback loop node involving eIF4E, the mTOR cascade, and p53.

Asunto(s)

Proteínas de Unión al ADN/genética , Factor 4A Eucariótico de Iniciación/genética , Factor 4E Eucariótico de Iniciación/genética , Papillomavirus Humano 18/genética , Proteínas Oncogénicas Virales/genética , ARN Mensajero/genética , Regiones no Traducidas 5'/genética , Línea Celular Tumoral , Codón Iniciador/genética , Proteínas de Unión al ADN/biosíntesis , Femenino , Regulación Viral de la Expresión Génica/genética , Células HEK293 , Células HaCaT , Células HeLa , Papillomavirus Humano 18/metabolismo , Humanos , Proteínas Oncogénicas Virales/biosíntesis , Iniciación de la Cadena Peptídica Traduccional/genética , ARN Viral/genética , Serina-Treonina Quinasas TOR/genética , Proteína p53 Supresora de Tumor/genética , Neoplasias del Cuello Uterino/tratamiento farmacológico , Neoplasias del Cuello Uterino/patología , Neoplasias del Cuello Uterino/virología