Anomaly In Tumor Suppressor Genes Discovered With Regards To Prostate Cancer, Paving Path To New Anti-Cancer Drugs
Source: Thailand Medical News Jan 12, 2020 4 years, 3 months, 2 weeks, 21 hours, 32 minutes ago
Similar to security screenings to make sure nothing harmful makes its way into a crowded area, cells in the human body use checkpoints to control their growth and prevent harmful mutations from making their way into new cell populations and causing trouble. Every cell that divides and replicates its DNA must clear at least three checkpoints – all of which call on specialized
genes known as
tumor suppressors.
Typically,
tumor suppressor genes encode proteins that work with other molecules in cells to put the brakes on cell division when DNA damage or other defects are detected. This process prevents mutations that harm cells or that lead to uncontrolled cell growth and cancer from being passed along to new cells. Fortunately,
tumor suppressors are fairly robust. Under normal circumstances, they stop working only when mutations affect both of the
tumor suppressor gene's alleles, which are the different forms of a gene inherited from each parent.
However in the case of
prostate cancer, researchers at the Lewis Katz School of Medicine at Temple University (LKSOM) and Fox Chase Cancer Center recently discovered an important exception to this two mutation rule. Working in human cells and animal models, they found that a mutation leading to the loss of just one allele of a
tumor suppressor gene known as
PPP2R2A is enough to make a tumor caused by other mutations worse.
A research study published in the journal
Oncogenesis, the team, led by Xavier Graña, PhD, Professor of Medical Genetics and Molecular Biochemistry, and in the Fels Institute for
Cancer Research and Molecular Biology at LKSOM, found that patients whose prostate tumors carry only one copy of
PPP2R2A do not survive as long as those whose tumors have two copies of the gene. They also showed that in cells deficient in
PPP2R2A, reconstitution of the
PP2A protein encoded by the gene ultimately kills
prostate cancer cells.
The research is the first to show that reactivating
PP2A in affected cells can slow or stop the advance of
prostate cancer in an animal model.
Dr. Graña explained to
Thailand Medical News, “The majority of
prostate tumors have only one functional copy of the
PPP2R2A gene. Because this alteration occurs so frequently, many patients could benefit from treatments that restore the gene's activity.”
The research team mapped out specifically what happens when cells lose a copy of
PPP2R2A, and what happens when
PP2A is reconstituted. When lost, they found that cells were more likely to divide and replicate, thereby generating more cells – a process that fuels cancer progression. This occurred because cells just breezed through the so-called mitotic check
point, which normally ensures that a cell's chromosomes are organized properly for cell division.
PP2A reactivation, on the other hand, resulted in sustained activation of the mitotic checkpoint – to the point that the cellular machinery responsible for separating replicated chromosomes for division collapsed, killing the cells.
Dr. Graña further explained, “Restoring
PP2A to normal levels in these
cancer cells caused a weakening of their centrosome, which is the organizer of the cell machinery in charge of faithfully separating chromosomes,” “The combination of a sustained checkpoint and a weakened centrosome results in collapse of the mitotic apparatus, with chromosomes not knowing where they have to go. Our findings indicate that
prostate tumors often kick off a copy of the
PPP2R2A gene to facilitate their growth and that bringing
PP2A levels back to normal results in abnormal chromosome sorting and cell death.”
Dr. Graña added, “Small molecules that activate
PP2A and that have the potential to be developed into drugs have already been identified. Whether they specifically activate
PP2A in
prostate cancer remains unclear, however. More work is needed to find a specific drug for this complex, but we have a promising start.”
Reference: Zhao, et al. (2019) PPP2R2A prostate cancer haploinsufficiency is associated with worse prognosis and a high vulnerability to B55α/PP2A reconstitution that triggers centrosome destabilization. Oncogenesis DOI: 10.1038/s41389-019-0180-9 
