Gonzalo's team has found a pathway responsible for the loss of 53BP1 in breast cancers with poor prognosis, specifically BRCA1 mutated and triple-negative. It turns out that loss of BRCA1 increases the expression of a protease, known as cathepsin L (CTSL), which causes the degradation of 53BP1. Cells that have lost both BRCA1 and 53BP1 have the ability to repair DNA, maintain the integrity of the genome, and proliferate. Thus, the protease helps cells with faulty BRCA1 to survive.
If lowering the levels of 53BP1 allows BRCA1 deficient cells to thrive and do their worst, increasing the levels of the protein offers a promising strategy for treatment of breast tumors.
So, how to do this? In previous research, Gonzalo's team showed that vitamin D inhibits CTSL-mediated degradation of 53BP1 in non-tumor cells, as efficiently as specific CTSL inhibitors. This time, they found that treatment of BRCA1-deficient tumor cells with vitamin D restores high levels of 53BP1, which results in increased genomic instability and reduced proliferation. Importantly, their evidence suggests that vitamin D treatment might restore the sensitivity to PARP inhibitors in patients who become resistant. Thus, a combination of vitamin D and PARP inhibitors could represent a novel therapeutic strategy for breast cancers with poor prognosis.
So, with this chain of events, Gonzalo and colleagues demonstrated a pathway by which triple-negative breast cancers proliferate: BRCA1-deficient cells activate CTSL which minimizes levels of 53BP1 to overcome genomic instability and growth arrest.
In a final except
|Contact: Carrie Bebermeyer|
Saint Louis University