title: Identification of a 17-nucleotide splicing enhancer in HPV-16 L1 that counteracts the effect of multiple hnRNP A1-binding splicing silencers.
abstract: Human papillomavirus type 16 (HPV-16) infections can in rare cases persist and cause lesions that may progress to cervical cancer. Cells in the lesions are not permissive for virus production, nor are cervical cancer cells. The intracellular environment is such that it prevents production of the highly immunogenic, viral structural proteins L1 and L2. One may speculate that inhibition of L1 and L2 expression is a prerequisite for persistence and cancer progression. We have therefore investigated how expression of HPV-16 L1 is regulated. We found that the only splice site in the HPV-16 late region, which is used to produce L1 mRNAs, is under control of a splicing enhancer located in the 17 nucleotides immediately downstream of the splice site. However, the function of this enhancer in cervical cancer cells is largely overshadowed by multiple splicing silencers in the late region which bind to hnRNP A1. High levels of hnRNP A1 therefore inhibit HPV-16 L1 expression. Immunohistological analysis of cervical epithelia revealed that hnRNP A1 is expressed primarily in the lower layers of the epithelium. hnRNP A1 is undetectable in terminally differentiated cells that can express HPV-16 late genes, which supports the conclusion that high levels of hnRNP A1 inhibit HPV-16 L1 expression.
authors.affiliation: Department of Medical Biochemistry and Microbiology, Uppsala University, Biomedical Center, Husargatan 3, Box 582, 751 23 Uppsala, Sweden.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Zhao
authors.forename: Joanna
authors.initials: J
authors.lastname: Fay
authors.forename: Helen
authors.initials: H
authors.lastname: Lambkin
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwartz
mesh_terms: D001483:Base Sequence; D036022:Capsid Proteins / Q000235:genetics* / Q000378:metabolism*; D002454:Cell Differentiation; D017931:DNA Primers / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D004742:Enhancer Elements, Genetic; D020868:Gene Silencing; D006367:HeLa Cells; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000235:genetics / Q000378:metabolism*; D052162:Human papillomavirus 16 / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000235:genetics* / Q000378:metabolism*; D012326:RNA Splicing; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism
chemical_list: D036022:Capsid Proteins; D017931:DNA Primers; D004279:DNA, Viral; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D009856:Oncogene Proteins, Viral; D012367:RNA, Viral; C063317:L1 protein, Human papillomavirus type 16