Abstract A26: GATA2 is necessary for oncogene-mutant non-small cell lung tumorigenesis
Authors: Kumar Madhu S. , Downward Julian 
Published: March 2013

Non-small cell lung cancer (NSCLC) is the most common histological cancer type in terms of both prevalence and mortality worldwide. In NSCLC, KRAS and EGFR are the most frequently mutated oncogenes, constituting half of all patients. Thus, there is a profound need to develop therapies targeting these lesions. To address this need, we previously performed an RNA interference screen for factors required in KRAS mutant cells. Through this screen, we found KRAS mutant cells depend on the transcription factor GATA2. Subsequent analysis of a broad panel of NSCLC lines revealed GATA2 depletion suppressed mutant cell viability. We then explored the role of GATA2 in NSCLC cells with a variety of oncogene mutations. We observed lethality with GATA2 loss in mutant NSCLC cells, with no effect in wild type NSCLC cells. Moreover, transplanted mutant NSCLC cells depleted for GATA2 exhibited abrogated tumor growth, while wild type tumors were unaffected, suggesting GATA2 is needed in oncogene-mutant NSCLC.

To elucidate the mechanism of GATA2 function in NSCLC gene expression, we performed gene expression analysis of mutant cells with GATA2 suppression. With GATA2 loss, we observed global downregulation of the proteasome and subsequent inhibition of proteasome activity. This inhibited proteasome function is biologically salient, as restoration of proteasome activity rescued growth in response to GATA2 depletion. We further explored the role of GATA2 in NSCLC by integrating the above gene expression data with global genome occupancy with chromatin immunoprecipitation coupled to next-generation sequencing (ChIP-seq). Through these approaches, GATA2 loss suppressed expression of the IL-1 signaling pathway in mutant cells, down-regulating pathway flux. Consequently, restored IL-1 signaling reestablished growth in response to GATA2 depletion. Moreover, GATA2 occupancy was enriched in Rho signaling pathway components, functionally inactivating Rho signaling. Accordingly, activated Rho signaling rescued viability in response to GATA2 loss. Analyzing the DNA motifs from our GATA2 ChIP of mutant NSCLC cells, we observed enrichment of the STAT5 response element at Rho target genes. We subsequently isolated a GATA2-STAT5 complex in mutant NSCLC cells. Overall, our integrative genomic analyses have revealed a transcriptional network governed by GATA2 in oncogene-driven NSCLC.

To examine the effect of GATA2 loss in genetically engineered mouse models (GEMMs) of NSCLC, we combined a conditional allele of Gata2 with Cre-inducible oncogenic Kras, where Gata2 deletion suppressed tumor growth compared to wild type animals. We then examined the role of whole-body loss of GATA2 in established lung tumors via systemic deletion of Gata2. In this system, GATA2 depletion caused complete regression of established lesions. We then explored whether inhibition of GATA2-regulated pathways with clinically approved compounds would recapitulate the effects of GATA2 loss in NSCLC GEMMs. To do so, we combined bortezomib, an inhibitor of the proteasome, and fasudil, an inhibitor of Rho signaling, in the Kras lung tumor model. Treatment of the Kras-mutant GEMM with these compounds caused a near-complete clearance of tumors. These combined genetic and therapeutic approaches reveal GATA2 is required for autocthonous oncogene-driven tumorigenesis and that combined inhibition of GATA2-controlled pathways with licensed agents suppresses NSCLC growth.

In sum, these results demonstrate GATA2 is necessary for oncogene-mutant NSCLC cell survival. Most strikingly, these findings suggest that the functional pleiotropy of GATA2, not a traditional druggable target, represents a network of druggable pathways for therapeutic exploitation.