Cancer cells display several characteristics that distinguish them from normal cells, including metabolic reprogramming that supports uncontrolled cell growth and alters metal ion homeostasis. Copper ion levels are elevated in cancer cells as many cancer-promoting processes involve copper-dependent enzymes. A key metabolic change involves the switch from aerobic to anaerobic respiration, leading to accumulation of intracellular protons. The efflux of protons acidifies the tumor microenvironment, activating metalloproteases that degrade the extracellular matrix and promote invasion and metastasis. Because of proton efflux, the intracellular environment becomes more basic; rising from around 7.2 in healthy cells to approximately 7.8 in cancer cells. These physicochemical changes in cancer cells may modulate folding, stability, and activity of cellular proteins. Here, we reveal that Grb2, a key regulator of the RAS/MAPK proliferation signaling pathway, is structurally affected by a pH increase mimicking cancer cells. Using a combination of biophysical techniques, such as DLS, CD, and NMR, we show that protein flexibility is increased at high pH and at this condition Grb2 accesses new conformations. Furthermore, fluorescence and STD-NMR experiments combined with molecular docking of the Grb2 interaction with coumarin, a known antiproliferation molecule, reveal that these interactions are pH dependent. We are currently extending this work to the tumor suppressor protein p53, which is mutated in the majority of cancers. Using biophysical tools, we assess how p53 unfolding is triggered by mutations, altered pH, and nonnative metal ion interactions. p53 has a functional zinc ion, but it can be displaced by copper. The aggregation of p53 to amyloids will be studied as a function of physicochemical alterations, and resulting amyloids structurally resolved.
Moreira et al. (Sun,) studied this question.