A recent study has identified a new breast cancer tumour suppressor protein that regulates the gene expression.
Researchers from the Nagasaki University discovered that a significant proportion of mice, lacking one of two Runx3 genes spontaneously developed mammary gland tumours at 14 or 15 months of life.
The age is equivalent to age 40 to 50 in human beings.
"People suggested that Runx3 might be a tumour suppressor in breast cancer because they found that it is down-regulated in a lot of breast cancer cell lines and breast cancer tissues," said University of Illinois medical biochemistry professor Lin-Feng Chen.
"We found mammary tumours growing in about 20 pc of the female mice lacking a copy of the Runx3 gene," Chen added.
The researchers also found that estrogen receptor alpha (ER-alpha), a well-known culprit in the development of many breast tumours was up-regulated in the mouse tumours.
Circulating estrogen binds to ER-alpha and initiates a chain of events that alter gene expression in the targeted cell.
This is a normal part of cellular signaling, but in ER-positive breast cancers, the overexpression of ER-alpha leads to enhanced tumour cell survival, growth and proliferation.
It was seen that when Runx3 was re-introduced into ER-alpha positive breast cancer cell lines, it suppressed the growth of the cancer cells and inhibited the potential of the cancer cells to form tumours in the mouse.
"By regulating the cellular levels of ER-alpha, Runx3 appears to control the cell's response to circulating estrogen, thus playing an important role in the onset of breast cancer," Chen explained.
The study has been published in the journal Oncogene.