A
digital representation of the human papillomavirus
Newly
identified proteins will help researchers to diagnose the human papillomavirus
lesions most likely to progress to cancer
Depending on the strain, or genotype, of the
human papillomavirus (HPV) (see image), the lesions it causes can range from
relatively benign to cancer-causing. Differentiating between lesions caused by
low-risk and high-risk viral genotypes, however, is difficult. Françoise
Thierry at the A*STAR Institute of Medical Biology in Singapore and co-workers
have now identified proteins that could be used as reliable, sensitive markers
to diagnose infections with high-risk types of HPV1.
Commonly known as an inducer of genital
warts, HPV is transmitted by sexual contact. Of the approximately 100 HPV
genotypes known, a few, including HPV-18, have a high likelihood of leading to
cervical or anal cancer. If pre-cancerous lesions are identified in their early
stages, they can usually be removed using simple surgical procedures, with a
very good prognosis.
The marker proteins identified by Thierry and
colleagues, called E2^E4, are natural fusions between two known HPV proteins,
E2 and E4. When Thierry and her co-workers discovered the fusion proteins, they
were investigating the activity of the HPV-18 E2 protein, using cells
engineered to express the E2 protein only. The results were repeatedly
‘contaminated’ by E4 protein.
Sequencing the HPV-18 E2 gene transcripts
revealed the source of the E4 sequences: the gene includes triggers to make the
E4 protein and attach it to the E2 protein. The DNA for the E4 gene is embedded
within the DNA for the E2 gene, just ‘shifted’ over by one DNA base — akin to
starting to read the word ‘intermittent’, and finding the word ‘mitten’ at the
sixth letter. Thus, cells infected with HPV-18 automatically produce E2^E4
along with E2.
Knowing that a protein unique to HPV-18 could
be clinically useful, the researchers checked the DNA sequences of other HPV
types and found that they could not produce the fusion protein. “Since E2^E4
transcripts (and proteins) are specific to HPV-18, they could be used to
unambiguously detect the presence and expression of this particular HPV
genotype in early stage lesions,” Thierry explains.
What makes the protein useful as a marker may
have even broader clinical implications. Because the proteins are specifically
expressed in only a few high-risk HPV types, the researchers suspect they may
not only mark but also contribute to these genotypes’ virulence. “We would like
to find out whether or not they are involved in the oncogenic potential of
HPV-18 compared to other high-risk HPV genotypes which do not express E2^E4,”
says Thierry.
The A*STAR-affiliated researchers
contributing to this research are from the Institute of Medical Biology
References
- Tan, C. L., Gunaratne, J., Lai, D., Carthagena, L.,
Wang, Q. et al. HPV-18 E2^E4 chimera: 2 new spliced transcripts and proteins
induced by keratinocyte differentiation. Virology 429, 47–56
(2012). | article
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