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Secrets of Retroviruses: Why Does Ross Sarcoma Virus Trigger Uncontrolled Cell Growth?
Rous Sarcoma Virus (RSV) is the first tumor virus discovered in history and is known for its ability to cause chicken tumors. As a retrovirus, when RSV infects a host, its RNA genome is transcribed into cDNA through a reverse transcription process and integrated into the host DNA. This process is an important milestone in cancer research because it reveals the molecular mechanisms of cancer development.
The discovery of RSV not only changed the way cancer research is conducted, but also opened the way for subsequent exploration of other tumor viruses.
In 1911, Peyton Rous at Rockefeller University revealed the carcinogenicity of this virus by injecting tumor-containing cell extracts into healthy "Plymouth Rock" chickens. He observed that these chickens developed symptoms of tumors, which are mainly composed of connective tissue, and the academic community recognized RSV as the first retrovirus that could be used to study the molecular development of cancer.
Roth therefore won the Nobel Prize in Physiology or Medicine in 1966 for his contribution to cancer research.
As research deepens, scientists have discovered that the genome structure of RSV is relatively complex. RSV belongs to class VI enveloped viruses and has a positive-sense RNA genome with DNA intermediates. Depending on the strain, the RSV genome can include up to four genes: gag (encoding capsid protein), pol (encoding reverse transcriptase), env (encoding envelope protein) and src (encoding tyrosine). kinase). These genes are not only involved in virus replication but also play an important role in transforming healthy host cells.
The presence of the src gene enables RSV to stimulate uncontrolled proliferation of host cells, which is one of the key factors in the development of cancer.
The src gene is also considered to be the first retroviral oncogene discovered. The presence of this gene can not only trigger abnormal proliferation of host cells, but also promote their susceptibility to viruses. Research shows that src genes are ubiquitous in the animal kingdom and are highly conserved among different species, demonstrating their importance in the evolutionary process.
Another feature closely related to RSV is the 3' untranslated region (3'UTR) of its RNA genome, which can be up to 5 to 7 kb in length, which often leads to nonsense-mediated degradation in the host cell. However, RSV possesses a conserved secondary structure called the Ross sarcoma virus stabilizing element (RSE). This structure can effectively prevent the degradation of viral RNA. On the one hand, it ensures the stability of the virus, and on the other hand, it promotes its stability in the host. of survival.
The presence of the RSE element shows the ingenious adaptations that retroviruses have developed in order to survive during their evolution.
The envelope structure of RSV is composed of a glycoprotein called env, which includes two glycoproteins, gp85 and gp37. After these glycoproteins bind to host cell receptors, they can directly promote the fusion of the virus into the host cell without changing the pH, so the entire infection process becomes relatively efficient.
After the virus enters the host cell, it first needs a primer to start the transcription process. RSV uses 4S RNA as a primer and 70S RNA as a template for DNA synthesis. Reverse transcriptase, as an RNA-dependent DNA polymerase, is responsible for transcribing viral RNA into a complete complementary DNA strand. This series of processes shows the efficiency and adaptability of RSV during the infection process.
Research on RSV not only helps scientists gain a deeper understanding of the development of cancer, but also promotes the exploration and research of other tumor viruses. With the advancement of science and technology, these studies are expected to further reveal the underlying mechanisms of tumor development and lay the foundation for the research of new treatments. After all, how many secrets do RSV and other tumor viruses hide that we have not yet discovered?
