|Education||BS, University of Michigan Ann Arbor|
Activating mutations in kinases serve as driver mutations for a large number of cancers, and numerous drugs have been developed, or are in development, to inhibit these hyper-activated proteins. However, complex interaction networks govern the activity and effects of mutated oncogenes, and phenomena such as feedback inhibition have complicated therapy development for numerous kinases, like RAS. While countless studies have probed and explored these gene interaction networks, very few have considered the functional differences and consequences of individual mutations in the same protein. A limited number of recent reports have begun to reveal that mutations in the same oncogene and even the same domain can have significantly different signaling and drug sensitivity profiles. Furthermore, our lab has shown that the presence of additional mutated oncogenes can synergize with and enhance these differences. These results suggest a previously unexplored level of complexity that is likely to influence the effectiveness of and resistance to various targeted therapies. My work will further test the effects of individual activating mutations in a gene and how they influence its interactions with other mutant proteins using physiologically accurate single and double knock-in (DKI) cell lines for the oncogenes HER2 and PIK3CA.
The human epidermal growth factor receptor 2 (HER2) is overexpressed in 20% of breast cancers. This overexpression leads to oncogenic amplification of receptor tyrosine kinase signaling and promotion of proliferation, survival, and motility. Fortunately, many years of work have led to the development of several drugs that act to reign in overactive HER2 signaling through various mechanisms (Herceptin, Lapatinib, etc…). Clinically, these drugs are used to treat patients that are designated as HER2 positive by assays for gene amplification and protein overexpression. Additionally, recent reports have identified somatic HER2 missense mutations in 2-4% of breast cancers, some of which have been shown to be activating and oncogenic through overexpression experiments. We have also shown that a more accurate modeling of these mutations through isogenic cell knock-ins can result in altered signaling and cell migration in some, but not all of the alterations. Patients whose tumors harbor these HER2 missense mutations will be classified as HER2 negative by current clinical evaluations, begging the question of whether they, too, will respond to HER2 directed therapies. Finding an answer may provide thousands of women per year with a previously unavailable treatment option or, conversely, prevent unnecessary overtreatment of these patients.
Our lab’s previous work has demonstrated that certain HER2 missense mutations result in tumorigenic cellular changes that can be reversed by HER2 directed therapies, but that these phenotypes are dependent on an additional PIK3CA E545K mutation. Furthermore, we discovered that the two most common hotspot mutations in PIK3CA, E545K (helical domain) and H1047R (kinase domain) result in differential phosphorylation profiles and protein interactions. PIK3CA is mutated in over 30% of breast cancers and these two hotspots account for more than 80% of these mutations, a number of which co-occur with HER2 missense mutations. Therefore, we hypothesize that the synergistic phenotypes seen in HER2 and PIK3CA double mutants will be notably different, depending on the specific mutations in each of the genes. We will test this hypothesis using numerous proliferation, migration, and drug assays.