Re: viral oncogene

[EMAIL PROTECTED] (KitKit) wrote in message news:<[EMAIL PROTECTED]>...
> hi everyone, i am a year one student of biology.
> i want to ask how viral oncogene infect its host? Is it the virus
> produce a lot of protein(for cell growth, proliferation or
> difficiation) which made of oncogene and INSERT them to the host. say
> ras or raf oncogene, which will disrupt the cell cycle of the host and
> produce a lot of cell.

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Viruses that carry oncogenes are now thought to be viruses which once
were not oncogenic but somewhere along the way, they accidentally
picked up some bits of genetic material from one of their hosts and
incorporated it into their own genome. It gets copied when the virus
replicates. It can stay the same or it can undergo mutation, which
won't affect viral survival since the virus didn't need that gene
anyway. When the now oncogenic viral progeny infect a new host, the
expression of the oncogene can cause cancerous transformation in any
of several ways. It can block expression of genes needed for cell
growth control, it can produce some factor that causes cells to
divide, it can disrupt some important enzyme or cell cycle pathway,
etc. Most oncogenes have been shown to be similar or even identical to
normal cellular genes, which by a sort of backward logic then became
known as "proto-oncogenes" (even though obviously that can't be their
real function!) or "tumor suppressor genes" which seem to be positive
growth-controlling genes that prevent excess cell division.  Some of
the cancer-causing viruses have even lost the ability to survive
independently and have integrated themselves into the host genome
permanently and lost some of their own replicative genes. The
oncogenes in these viruses may get turned on during the course of the
life of the host cell, and this can set off a cancer.

Not all cancer-causing viruses contain oncogenes. Some just have the
property of integrating into the host genome right in the middle of
some important tumor suppressor gene or other site, the destruction of
which can mess up an important control pathway. Others, when they
integrate and start to express their own genes, can cause
"read-through" of the host's downstream genetic information,
activating cell proliferation genes that would normally have been
turned off.

This is a very simplified explanation and leaves out a lot of other
factors in virus-related carcinogenesis, but I hope it answers your
question at least partially. You can probably find a lot of good
articles in back issues of "Scientific American" that will explain
viral carcinogenesis in simple terms. If you want more detailed
articles, go to www.ncbi.nlm.nih.gov, select PubMed from the menu, and
in the Search box, type: oncogenes AND tumor viruses [mh] AND review
[PT]  This will get you a big list of references to review articles
about this topic, and you can click on the ones you are interested in
to read the abstract and click on "Related" to get more references to
similar articles.

Keep asking good questions!
Good luck,
Helen Stanbro