PROJECT SUMMARY
As tumors progress, cancer cells acquire characteristics that allow them to adapt to various stresses. In fact,
one of the best predictors of patient outcome is disease stage at the time of diagnosis, as advanced tumors are
more aggressive and difficult to treat. However, the underlying mechanisms that potentiate increased cell
plasticity throughout cancer progression remain poorly understood. The ability of cancer cells to adapt has
posed a particular problem for the use of targeted therapies, which are frequently rendered ineffective by the
emergence of acquired resistance. The goal of this work is to elucidate molecular mechanisms that regulate
the cell cycle and cell fate decisions to influence cancer progression and resistance to targeted therapy. In the
F99 phase, I aim to identify novel factors that regulate the retinoblastoma (RB) pathway and influence the
cellular response to inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6). CDK4/6, in complex with Cyclin
D, phosphorylate and inactivate the tumor suppressor RB to drive cell cycle progression. Recently developed
CDK4/6 inhibitors have shown some promise in the clinic, but every patient given these inhibitors eventually
progresses, creating an urgent need to identify mechanisms of resistance. Using an in vitro genome-wide
CRISPR/Cas9 screen, I recently identified loss of the E3 ligase adaptor AMBRA1 as a potential mechanism of
resistance to CDK4/6 inhibition. Further, AMBRA1 loss increased Cyclin D protein stability. I hypothesize that
AMBRA1, with its accompanying E3 ligase complex, targets Cyclin D for degradation, and that AMBRA1 loss
could be a mechanism of resistance to CDK4/6 inhibitors in vivo. I will use molecular and biochemical assays
to identify the E3 ligase that cooperates with AMBRA1 to target Cyclin D. In addition, I will combine tumor
barcoding with multiplexed CRISPR/Cas9-mediated gene targeting in mouse models of non-small cell lung
cancer to determine whether loss of AMBRA1 leads to CDK4/6 inhibitor resistance in vivo. In the K00 phase, I
aim to elucidate the molecular mechanisms regulating cell identity in lung adenocarcinoma (LUAD). Treatment
of LUAD with small molecule inhibitors targeting mutant receptor tyrosine kinases can lead to relapsed tumors
that have transdifferentiated into small cell lung cancer, an aggressive neuroendocrine cancer with limited
treatment options. However, the mechanism of transdifferentiation is largely unknown. I propose to develop cell
line and mouse models of this transdifferentiation process in order to identify factors that regulate LUAD cell
identity and ultimately identify means to prevent or reverse transdifferentiation. Together, this body of work will
elucidate fundamental principles of acquired resistance and disease progression in lung cancer, which may
also be applicable to other cancer types.