Work by University of California Researchers has paved way in identification of Bmi-1 protein that results in the transformation of healthy cells into prostrate cancer cells. Bmi-1 protein in prostate cell plays a critical role in regulation of normal prostate cells, repairing worn out cells and recovering normal cells killed by hormone withdrawal therapy.
The findings, by researchers with the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA, may have important implications for controlling cancer growth and progression.
The protein, called Bmi-1, is often up-regulated in prostate cancer, has been associated with higher grade cancers and is predictive of poor prognosis, according to previous studies.
However, its functional roles in prostate stem cell maintenance and prostate cancer have been unclear, said Owen Witte, senior author of the study.
A study of loss and gain of function in prostate stem cells indicated that Bmi-1 expression was required for self-renewal activity and maintenance of prostate stem cells with highly proliferative abilities.
Loss of Bmi-1 expression blocks the self-renewal activity, protecting prostate cells from developing abnormal growth changes which can lead to cancer.
More importantly, Bmi-1 inhibition slowed the growth of an aggressive form of prostate cancer in animal models, in which the PTEN tumor suppressor gene was removed allowing the cancer to run wild, Witte said.
"We conclude by these results that Bmi-1 is a crucial regulator of self-renewal in adult prostate cells and plays important roles in prostate cancer initiation and progression.
"It was encouraging to see that inhibiting this protein slows the growth of even a very aggressive prostate cancer, because that could give us new ways to attack this disease," said Witte.
UCLA stem cell researchers have been studying the mechanisms of prostate stem cells for years on the theory that the mechanism that gives the cells their unique ability to self-renew somehow gets high jacked by cancer cells, allowing the malignant cells to grow and spread.
If the mechanism for self-renewal could be understood, researchers could find a way to interrupt it once it is taken over by the cancer cells, Witte said.
Rita Lukacs, first author of the study, found that Bmi-1 inhibition also stops excessive self-renewal driven by other pathways. This has suggested that the Bmi-1 pathway may be dominant to other genetic controls that affect the cancer phenotype.
"Prostate cancer can be initiated by so many different mutations, if we can find a key regulator of self-renewal, we can partially control the growth of the cancer no matter what the mutation is.
"We're attacking the process that allows the cancer cells to grow indefinitely. This provides us an alternate way of attacking the cancer by going to the core mechanism for cancer cell self-renewal and proliferation," said Lukacs.
The study appeared in the journal Cell Stem Cell.