Oncogenic comparison of human papillomavirus type 58 E7 variants

Human papillomavirus 58 (HPV58) ranks the second or third in East Asian cervical cancers. Current studies on HPV58 are scarce and focus on the prototype. Previously, we identified the three most common circulating HPV58 E7 strains contained amino acid alterations: G41R/G63D (51%), T20I/G63S (22%) and T74A/D76E (14%) respectively. Among them, the T20I/G63S variant (V1) had a stronger epidemiological association with cervical cancer. We therefore suggested that V1 possessed stronger oncogenicity than the other two variants. Here, we performed phenotypic assays to characterize and compare their oncogenicities with HPV58 E7 prototype. Our results showed that overexpression of V1 conferred a higher colony-forming ability to primary murine epithelial cells than prototype (P < 0.05) and other variants, implicating its higher immortalising potential. Further experiments showed that both V1 and prototype enhanced the anchorage-independent growth of NIH/3T3 cells (P < 0.001), implicating their stronger transforming power than the two other variants. Moreover, they possessed an increased ability to degrade pRb (P < 0.001), which is a major effector pathway of E7-driven oncogenesis. Our work represents the first study to compare the oncogenicities of HPV58 E7 prototype and variants. These findings deepened our understanding of HPV58 and might inform clinical screening and follow-up strategy.

Identification of a recurrent transforming UBR5-ZNF423 fusion gene in EBV-associated nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a distinct type of head and neck cancer which is prevalent in southern China, south-east Asia and northern Africa. The development and stepwise progression of NPC involves accumulation of multiple gross genetic changes during the clonal expansion of Epstein–Barr virus (EBV)-infected nasopharyngeal epithelial cell population. Here, using paired-end whole-transcriptome sequencing, we discovered a number of chimeric fusion transcripts in a panel of EBV-positive tumour lines. Among these transcripts, a novel fusion of ubiquitin protein ligase E3 component n-recognin 5 (UBR5) on 8q22.3 and zinc finger protein 423 (ZNF423) on 16q12.1, identified from the NPC cell line C666-1, was recurrently detected in 12/144 (8.3%) of primary tumours. The fusion gene contains exon 1 of UBR5 and exons 7–9 of ZNF423 and produces a 94 amino acid chimeric protein including the original C-terminal EBF binding domain (ZF29-30) of ZNF423. Notably, the growth of NPC cells with UBR5–ZNF423 rearrangement is dependent on expression of this fusion protein. Knock-down of UBR5–ZNF423 by fusion-specific siRNA significantly inhibited the cell proliferation and colony-forming ability of C666-1 cells. The transforming ability of UBR5–ZNF423 fusion was also confirmed in NIH3T3 fibroblasts. Constitutive expression of UBR5–ZNF423 in NIH3T3 fibroblasts significantly enhanced its anchorage-independent growth in soft agar and induced tumour formation in a nude mouse model. These findings suggest that expression of UBR5–ZNF423 protein might contribute to the transformation of a subset of NPCs, possibly by altering the activity of EBFs (early B cell factors). Identification of the oncogenic UBR5–ZNF423 provides new potential opportunities for therapeutic intervention in NPC. © 2013 The Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

The cellular oncogene EWS/activating transcription factor 1 is unable to activate adenovirus-borne promoters: implications for cytotoxic prodrug therapy of malignant melanoma of soft parts

The cellular oncoprotein Ewing's sarcoma oncogene (EWS)/activating transcription factor 1 (ATF1) is a highly specific marker for malignant melanoma of soft parts (MMSP) and is a potent activator of several cAMP-inducible promoters, including the somatostatin promoter. Here we explored the potential for using the somatostatin promoter to direct toxic gene expression in MMSP cells. When introduced into MMSP cells, a somatostatin-herpes simplex virus thymidine kinase fusion gene confers strong and cell-specific sensitivity to the cytotoxic prodrug ganciclovir. Ganciclovir sensitivity requires the ATF-binding site present in the somatostatin promoter, indicating that toxic gene expression is caused by EWS/ATF1. We also tested the efficacy of recombinant adenoviruses adenoviruses for gene delivery and expression in two MMSP cell lines (DTC1 and Su-ccs-1). Surprisingly, several promoters (including somatostatin) that are strongly activated by EWS/ATF1 in transient assays are not activated in DTC1 and Su-ccs-1 cells when present in an adenovirus vector. In summary, our findings demonstrate the potential for using the somatostatin promoter for cytotoxic prodrug therapy for MMSP. However, first-generation adenovirus vectors cannot be used as promoter delivery vehicles for toxic gene expression in MMSP cells.