At any given time, human cells contain about 12,000 proteins that work through signaling pathways to carry out the work of the cell, such as metabolism and the cell’s response to stress. The highly sensitive mass spectrometry system developed by Dr. Yu and his colleagues and first described in a 2013 Nature Methods article can pick out 200 or so modified, or tagged, proteins that form the PARP1 response signature. He compared his system to a shopper buying a watermelon at a grocery store where a bar code scanner is used to identify the particular type of melon being purchased.
In reference to the cancerous and noncancerous cells studied here, the chemical tag (or bar code) takes the form of a cluster of atoms that have a distinctive weight that can be measured with a sensitive mass spectrometer. Because chemical tags are part of the cancer cell’s efforts to set off signaling pathways to repair DNA, a better understanding of those pathways could result in new treatment targets.