Naturally Occurring Variations Modulate the Activity of the HPV33 Early Promoter and its Affinity for the E2 Transcription Factor

Transcriptional activity of the long control region in human papillomavirus type 33 intratype variants

BACKGROUND

High-risk human papillomaviruses (HPVs) are responsible for the development of cervical and other anogenital cancers. Intratype sequence variants of certain high-risk HPV types (e.g. 16, 18 and 31) are thought to have different oncogenic potential, partly due to nucleotide sequence variation in the viral long control region (LCR). The LCR has an important role in the regulation of viral replication and transcription. The purpose of this study was to explore sequence variation in the LCR of HPV 33 intratype variants in Hungary and to see whether there are differences in the transcriptional activities of the variants.

METHODS

The complete HPV 33 LCR was amplified from HPV 33 positive cervical samples. After sequencing the LCR variants, multiple sequence alignment and phylogenetic analyses were carried out. Representative HPV 33 LCR sequence variants were selected for cloning and functional analysis. After transient transfection of HeLa cells, luciferase reporter assays were used to analyse the transcriptional activities of different LCR variants.

RESULTS

Altogether 10 different variants were identified by sequence analysis of the HPV 33 LCR. The results of phylogenetic analysis showed that 3 variants belonged to sublineage A1, while the other 7 variants clustered with sublineage A2. Variants belonging to sublineage A2 had significantly lower transcriptional activities than variants belonging to sublineage A1. Within sublineage A2, the two variants analysed had significantly different transcriptional activities, which was shown to be caused by the A7879G variation.

CONCLUSIONS

Nucleotide variation in the HPV 33 LCR can result in altered transcriptional activity of the intratype variants. Our results can help to understand the correlation between LCR polymorphism and the oncogenic potential of HPV 33 variants.

Functional evaluation of human papillomavirus type 31 long control region variants

Persistent infections by high-risk human papillomavirus (HR-HPV) are a necessary condition, but not sufficient for cervical cancer development. Genetic variants of HR-HPV appear to be related to the risk of persistent infections. The study performed a functional evaluation of variants of the HPV-31 promoter region (LCR). For this, cloning and subcloning of variants HPV-31/UFPE-21 HPV-31/UFPE-89, HPV-31/UFPE-66, E2 gene and prototype HPV-31 were performed. Transfection with different concentrations of E2 was done and the concentration of 25 ng was determined to be ideal for LCR activation. HPV-31/UFPE-21 and HPV-31/UFPE-89 have a greater ability to alter Nluc reporter gene expression levels and HPV-31/UFPE-66 showed decreased levels of gene expression of Nluc reporter gene compared to control. Statistical analysis showed a significant difference between the polymorphic LCR regions and the control (p < 0.0001). A more refined profile of variants of HPV-31 and its importance for the prognosis of cervical lesions begins to be drawn.

Orientation-dependent toxic effect of human papillomavirus type 33 long control region DNA in Escherichia coli cells

The functional analysis of human papillomavirus (HPV) sequence variation requires the molecular cloning of different genomic regions of virus variants. In this study, we report an unexpected difficulty experienced when trying to clone HPV33 long control region (LCR) variants in Escherichia coli. Standard cloning strategies proved to be inappropriate to clone HPV33 LCR variants in the forward orientation into a eukaryotic reporter vector (pGL2-Basic). However, by slight modification of culture conditions (incubation at 25 °C instead of 37 °C), constructs containing the HPV33 LCR variants in the forward orientation were obtained. Transformation experiments performed with different HPV33 LCR constructs indicated that there is a sequence element in the 5′ LCR of HPV33 causing temperature-dependent toxic effect in E. coli. Sequence analysis revealed the presence of an open reading frame (ORF) in the 5′ part of HPV33 LCR potentially encoding a 116-amino acid polypeptide. Protein structure prediction suggested that this putative protein might have a structural similarity to transmembrane proteins. Even a low-level expression of this protein may cause significant toxicity in the host bacteria. In silico analysis of the LCR of HPV33 and some other HPV types belonging to the species Alphapapillomavirus 9 (HPV31, 35 and 58) seemed to support the assumption that the ORFs found in the 5′ LCR of these HPVs are protein-coding sequences. Further studies should be performed to prove that these putative proteins are really expressed in the infected host cells and to identify their function.

Characterization of an HPV33 natural variant with enhanced transcriptional activity suggests a role for C/EBPβ in the regulation of the viral early promoter

The Long Control Region (LCR) of the human papillomavirus (HPV) genome encompasses the early promoter (EP) that drives expression of the viral oncogenes in infected cells and HPV-associated cancers. Here, we report on a natural variant of HPV33 that displays higher EP activity than the prototype in transfected C33A and HeLa cervical carcinoma cells, and in the osteosarcoma U2OS cell line which supports replication of HPV episomes. This increased promoter activity was ascribed to a single nucleotide variation in the LCR, T7791C, in a putative binding site for the transcription factor C/EBPβ. T7791C abrogated binding of recombinant C/EBPβ to this site in vitro and stimulated the EP in vivo, suggesting that it abrogates a negatively-acting regulatory element. A second C/EBPβ binding site was identified in vitro that activated the EP in vivo and whose function and location in the epithelial-specific enhancer is shown to be conserved in the highly prevalent HPV18. These results suggest that C/EBPβ is both an activator and a repressor of the HPV33 EP, acting via two distinct binding sites. Prediction of C/EBPβ sites in the LCR of 186 HPV types suggests that C/EBPβ regulation of the EP is common among high‐risk viruses from the α genus.

Long noncoding RNA LINC00483/microRNA-144 regulates radiosensitivity and epithelial-mesenchymal transition in lung adenocarcinoma by interacting with HOXA10

Lung adenocarcinoma (LAD) is the leading cause of cancer death worldwide. Long noncoding RNAs (lncRNAs) have been shown to play an important regulatory role in cancer biology, including that of LAD. The aim of this experiment was to explore the interaction of LINC00483, microRNA-144 (miR-144), and homeobox A10 (HOXA10), and their effects on radio sensitivity and epithelial-mesenchymal transition (EMT) of LAD. Initially, microarray analysis was used to screen out miRNAs and lncRNAs, as well as the differentially expressed genes related to LAD. Following the screening process, the targeting relationship of LINC00483, miR-144, and that of miR-144 and HOXA10 was determined. Following that, the expression of LINC00483, miR-144, messenger RNA (mRNA), as well as protein expression of HOXA10, MMP-2, MMP-9, E-cadherin, vimentin, and N-cadherin that followed in cells was determined. Also, the effect of LINC00483 on cell migration and invasion ability, and cell tumorigenic ability was detected. LINC00483 and HOXA10 were found to be upregulated whereas miR-144 was downregulated in LAD. Silencing of LINC00483 could competitively bind to miR-144, thereby upregulating HOXA10. LINC00483 or HOXA10 silencing led to decreased HOXA10, MMP-2, MMP-9, vimentin, and N-cadherin but elevated miR-144 and E-cadherin. Moreover, after being transfected with silenced LINC00483, the cell proliferation, migration, and invasion were inhibited with enhanced radiosensitivity. Consequently, the data of the study indicates that interference of LINC00483 weakens its competitive binding ability to miR-144, thus reducing HOXA10 expression, and enhancing radiosensitivity in LAD.