A Drosophila model of HPV-related carcinoma has been developed using the papillomavirus E6 gene HPV18\E6 plus the human ubiquitin ligase gene Hsap\UBE3A expressed in the eye or wing disc. Co-expression of HPV18\E6 and Hsap\UBE3A results in visible phenotypes in disc-derived tissues not observed for expression of either gene alone; however, phenotypes indicative of cellular transformation or tumorigenesis are not observed. When, in addition, activated Ras85D or activated Notch N is expressed, tumorigenic phenotypes and evidence of metastatic cell migration are observed. This model has been extended using the papillomavirus E5, E6, and E7 genes HPV16\E5, HPV16\E6, and HPV16\E7 genes, in which all three genes are co-expressed in the eye disc with Hsap\UBE3A.
Using the eye phenotype, this system has been used to identify the signaling pathways involved in E6 + UBE3A phenotypes; a dominant negative form of the insulin receptor InR exacerbates the phenotype, implicating insulin signaling in this process. Effects upon Drosophila orthologs of known targets of E6 in human cells have been assessed; of the genes tested, the most significant effect was upon the molecular scaffolding protein Dmel\Magi (orthologous to human MAGI1, MAGI2, and MAGI3). A genetic screen identified Dmel\IKKβ as a modifier of the eye phenotype; this interaction is conserved in human cells.
UBE3A acts in the ubiquitin proteasome pathway and as a transcriptional coactivator. There is a single orthologous gene in Drosophila, Dmel\Ube3a, for which classical amorphic alleles, RNAi targeting constructs, and alleles caused by insertional mutagenesis have been generated. In analogous experiments, HPV18\E6 co-expressed with the fly Dmel\Ube3a gene in discs fails to produce visible phenotypes, and thus has not been used in this model.
The constitutively active Ras85D mutation, Ras85DV12, is analogous to oncogenic mutations found in human RAS proteins. Variant(s) implicated in human disease tested (as analogous mutation in fly gene): G12V in the fly Ras85D gene (corresponds to G12V in the human KRAS and HRAS genes). See also the human disease model report 'cancer, multiple, RAS-related' (FBhh0000474). Much of the work in flies investigating the role of the Notch pathway in development of cancer has involved combining Notch signaling dysregulation with another cancer model. This is typically achieved by using targeted expression of an activated form of Notch (N); see also the human disease model report 'cancer, multiple, Notch signaling pathway' (FBhh0000766).
[updated Jan. 2023 by FlyBase; FBrf0222196]
HPV is thought to be responsible for more than 90% of anal and cervical cancers, about 70% of vaginal and vulvar cancers, and 60% of penile cancers. Cancers of the oropharynx (back of the throat, including the base of the tongue and tonsils) traditionally have been associated with use of tobacco and alcohol, but recent studies show that about 60% to 70% of cancers of the oropharynx may be linked to HPV (https://www.cdc.gov/cancer/hpv/basic_info/cancers.htm).
Human papillomaviruses (HPVs) are the etiological agents in nearly all cases (99.7%) of cervical cancer, and the HPV E6 protein is one of two viral oncoproteins that is expressed in virtually all HPV-positive cancers. HPV16 and HPV18 are the high-risk types most frequently associated with cervical squamous cell carcinomas (50% and 20%, respectively). The HPV E6 and E7 proteins are the only two viral genes expressed in virtually all HPV-positive cervical carcinomas (Beaudenon and Huibregtse, 2008; pubmed:19007434).
E7 is the major transforming oncoprotein of HPV. It promotes increased cell proliferation by dysregulating the G1/S transition, and delays cell differentiation. E6 and E7 can each immortalize cells, but appear to act cooperatively in tumor formation, with E7 being involved in the early stages and E6 accelerating progression to malignancy. A third HPV protein, E5, expressed early in the HPV life cycle, provides support for viral infection and transformation of cells. E5 enhances the oncogenic abilities of E6 and E7 in cellular transformation and tumor formation. (Hashemi, et al., 2022, pubmed:36508448; FBrf0255248 and references cited therein).
High-risk HPV E6 proteins bind directly to the cellular ubiquitin ligase E6AP/UBE3A, causing its substrate specificity to be altered so that it stably associates with and polyubiquitylates TP53, resulting in degradation of TP53 (Beaudenon and Huibregtse, 2008; pubmed:19007434).
Multiple functions of E6, including interaction with UBE3A, TP53 and PDZ domain-containing substrates, appear to be required for its ability to bring about cell transformation and to contribute towards malignancy in animal models (Beaudenon and Huibregtse, 2008, pubmed:19007434; FBrf0233222 and references cited therein).
One to one: 1 human to 1 Drosophila
High-scoring ortholog of human genes KRAS, HRAS, and NRAS (many to many; multiple paralogs and orthologs in both species). Dmel\Ras85D shares 78-86% identity and 86-92% similarity with KRAS, HRAS, and NRAS; for these three human genes, Ras85D is the highest-scoring ortholog in Drosophila.
Moderate- to high-scoring ortholog of human NOTCH1, NOTCH2, NOTCH3, NOTCH4 (1 Drosophila to 4 human). Dmel\N shares 43-44% identity and 56-57% similarity with NOTCH1 and NOTCH2.