6: Human polyomavirus (PoV) can cause cancer, but it is not known exactly how. P
ID: 203721 • Letter: 6
Question
6: Human polyomavirus (PoV) can cause cancer, but it is not known exactly how. PoV integrates into the human DNA in the middle of a gene called MyBPC, which is a myosin binding protein. MyBPs are neither oncogenes nor tumor suppressor genes, though. So we have to form a hypothesis and test it. The figure shows virus insertion into the MyBPC gene. The part of the virus that inserts has a promoter (blue area). It also encodes a gene, VP1, and a short stretch called Agno that might or might not encode a gene. Integration occurs in the VP1 sequence, splitting it as shown. When the provirus is transcribed, it produces an mRNA that is a fusion between VP1 and MyBPC. Because this fusion does not maintain the MyBPC's normal reading frame, when the fusion mRNA is translated, a premature stop codon occurs at the location marked by *. VP1-MYBPC1 Fusion Protein MYBPC1 Agno VP-1 MYBPC1 MYBPC1 PoV PoV provirus A. Suggest THREE specific ways in which this viral insertion might cause tumor formation For each hypothesis, suggest which protein is involved, and what it might be doing to cause tumor formation. 19 B. Now think of a technique that could be used to test each of your three hypotheses. What experiment could you do, and what would you look for to prove or disprove each hypothesis? 17Explanation / Answer
We can assume three hypothesis on the basis of genes present for PoV.
In the hypothesis 1 both proviral gene Agno and VP1 are inserted in host genome and both are expressed (because it has promotomer sequences are present so it may be transcribed). mRNA for Agno and VP1 gene codes for viral protein which later on become carcinogenic.
In the second hypothesis suppose only VP1 gene is expressed, here premature stop codon will stop the transcription exact protein for MyBPC1 is not formed, however viral VP1 gene translated and can form viral protein and it is virulentwhich later on become carcinogenic.
If only Agno gene is transcribed, than it is enough for virus to survive and induced cancer. Noticeablly in all three cases MyBPC1 gene or its premature termination do not have any involvement to induce cancer.
Technique
We can use sequence based PCR technique to check our hypothesis. In this technique if we prepared three set of primers (primer for gene Vp1, primer for Gene Argo and primer for VP1-MyBPC1 junction).
these three PCR reaction are set in three different tubes along with control (tube having MyBPC1 primer). this reactions are carried out at primer specific annealing temperature and results were analysed on agarose gel electrophoresis. the gene which is inserted is amplified and will give DNA band on agarose gel.
By conducting, three different PCR reaction using three different primer set in each hypothesis we can say that which gene is inserted and will be expressed to causes cancer. Proving one of the three hypothesis will disproven the other two and PCR will helps in it.
we can also use RT-PCR technique for quantitatively measuring the expression of gene inserted.
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