Tyrosine kinases are key regulators in the cell, controlling core processes such as growth, differentiation, migration and death. Activation of these enzymes at the wrong time and place, however, may lead to cancer. Recently, drugs targeting some of the 90 different tyrosine kinases encoded by the human genome have met with success in treating various cancers. The race is now on to discover new drug targets in this protein family and to determine which cancers will respond to which drugs.
Many efforts have focused on high-throughput methods to scan the cancer genome for mutations, but cancer genes sometimes exert their effects at the protein level, highlighting the need for proteomic approaches to illuminate protein behavior.
Howard Hughes investigator Todd Golub, an HMS associate professor of pediatrics at Dana–Farber Cancer Institute and Children’s Hospital Boston, led a study published in the January Nature Biotechnology that systematically examines the activation state of tyrosine kinases in cancer cells. Armed with the knowledge that phosphate groups are attached to these kinases when activated, postdoctoral researcher Jinyan Du assembled a collection of 62 antibodies, each of which binds specifically to a different tyrosine kinase, and a rainbow array of tiny fluorescent beads with a different color assigned to each antibody. Antibody-coated beads were used to fish out the tyrosine kinases from the protein lysates of 130 different cancer cell lines. Then, a general-purpose antibody recognizing all phosphorylated tyrosine kinases was used to fluorescently tag the activated proteins. Finally, the beads were sorted using two lasers, one detecting the specific tyrosine kinase and the other determining its phosphorylation state.
This inexpensive, high-throughput proteomics method developed by Golub’s lab detected the phosphorylation of many tyrosine kinases that are genetically altered in various cancers, confirming the validity of the approach. However, it also identified novel players not commonly mutated in cancer.
“This finding illustrates that there exist cancer-causing proteins whose role in cancer was not suggested at the level of the genome,” said Golub, who is also an investigator at the Broad Institute.
One such protein is SRC, which was frequently activated in cell lines from patients with glioblastoma, the most common and aggressive type of brain tumor. Du and colleagues found that tissue samples from glioblastoma patients showed SRC activation and that the SRC inhibitor dasatinib decreased proliferation and migration and increased apoptosis in cancer cell lines. Moreover, the drug reduced tumor growth in mice injected with glioblastoma cells. Future goals of the lab include elucidating the mechanism by which SRC is activated and how this might lead to disease.
Students may contact Todd Golub at golub@broad.harvard.edu for more information.
Conflict Disclosure: The authors report no conflicts of interest.
Funding Sources: Leukemia and Lymphoma Society, the Irving Family, the Brain Tumor Funders’ Collaborative, the National Cancer Institute's Initiative for Chemical Genetics and the National Institutes of Health
