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The surprising link between MMTV and hormones: why does it become active after puberty?
Murine mammary tumor virus (MMTV) is a retrovirus transmitted through milk. It is similar to HTL virus, HI virus and BLV virus and belongs to the new genus of retrovirus. The early name of MMTV was Bittner virus. This name originated from the research conducted by John Joseph Bittner at the Jackson Laboratory in Maine, USA in 1936. He proposed a theory called "milk factor". It was pointed out that cancerous mother mice can pass cancer factors to their young mice through breast milk. The occurrence of most mouse mammary tumors is closely related to MMTV.
With the onset of puberty, the virus enters the mammary gland and initiates replication in multiplying mammary epithelial cells.
During adolescence, the activity of MMTV increases significantly, and the virus enters the breast through blood circulation, which is closely related to hormonal changes. The genome of MMTV can be inserted into the host's genome, which allows the viral DNA to change gene expression and potentially form oncogenes once it is embedded in the host's genes.
Research shows that the process of MMTV infection has its specific life cycle. While some strains of mice carry the virus endogenously, it can also be transmitted vertically through breast milk. When the glands of mice develop to puberty, MMTV will enter the mammary gland along with migrating lymphocytes. This process is closely related to changes in hormone levels.
After puberty, all breast cells will contain active retroviruses and express the viral messenger RNA in new breast tissue cells.
Further activation of MMTV is related to the influence of estrogen. This hormone promotes the expression of viral genomes, leading to high levels of tumor-promoting factors in breast cells.
In the laboratory, researchers often use MMTV long terminal repeats (LTRs) to build experimental models that simulate human breast cancer. The glucocorticoid-responsive element contained in this sequence allows scientists to study the role of MMTV in cancer development.
MMTV-promoting factors are used in multiple mouse breast cancer model systems, which have provided valuable insights into human breast cancer.
In addition, MMTV has the ability to pass the virus to future generations through endogenous and exogenous pathways. When young mice are infected with the virus through breast milk, their probability of developing tumors is significantly increased, while those mice that already carry MMTV during embryonic development contain the DNA of the virus in every cell in their body.
It is worth noting that the activity of MMTV is also related to steroid hormones and prolactin. These hormones play critical regulatory roles in mammary gland development and lactation in mice. When mice reach puberty, MMTV's messenger RNA is expressed in estrogen-sensitive tissues, allowing the entire mammary cell system to be affected by the virus.
When viral DNA is embedded into the host genome, MMTV can autonomously transcribe its own viral genes, further increasing the possibility of cancer.
Through these discoveries, the scientific community has gradually deepened its understanding of the relationship between MMTV and hormones. These studies not only reveal the mechanism of breast cancer in mice, but also provide new ideas for the prevention and treatment of human breast cancer.
In this scientific field that is increasingly paying attention to the relationship between viruses and cancer, we cannot help but ask, can these studies finally answer the cancer problems faced by humans?
