Wang, Li

Abstract The RBBP4/p300 complex was recently shown to control genes critical for DNA damage repair and may play a role in glioblastoma (GBM) therapy responsiveness, especially to temozolomide (TMZ). However, the role of this complex in the modulation of the GBM tumor microenvironment (GBM-TME) remains elusive. Because pro-tumorigenic GBM-TME is primarily due to angiogenesis and immune tolerance, we evaluated whether the RBBP4/p300 complex may control these critical processes. To that end, we used shRNA to silence each RBBP4/p300 complex member in GBM43 cells and RNAseq to identify angiogenesis and immune genes regulated by this complex. Our data demonstrated that silencing RBBP4 or p300 suppressed the expression of HIF1α and several other hypoxia response genes, including VEGFA and DDIT4, suggesting that RBBP4/p300 complex may regulate angiogenesis. Consistent with a role in regulating angiogenesis, culture medium conditioned by GBM43 cells expressing the control non-targeting shRNA (shNT) significantly induced angiogenic tube formation by human umbilical vein endothelial cells (HUVEC). In contrast, this effect was blocked by the medium conditioned by the shRBBP4 or shp300 expressing cells. Both shRBBP4 and shp300 expressing cells failed to activate HIF1α accumulation and other signaling in response to hypoxia. Additionally, the control shNT-conditioned medium inhibited IFN-γ production while the medium conditioned by the shRBBP4 or shp300 expressing cells supported IFN-ɣ production from CD8+ T cells. Intriguingly, silencing RBBP4 or p300 also suppressed the expression of CCL2 and PD-L1 (CD274). CCL2 protein is a chemokine that promotes TME infiltration by myeloid-derived suppressor cells (MDSCs), while PD-L1 interacts with PD1 to suppress cytotoxic CD8+ T cell activation. Although this is an ongoing investigation, we conclude that RBBP4/p300 complex mediates the expression of hypoxia response genes, including HIF1α, and immunosuppressive genes, including PD-L1, and this activity may enhance angiogenic and immunosuppressed GBM-TME, making this complex a potential target for GBM therapy.

Abstract Lung cancer is the deadliest and most frequently diagnosed type of tumor worldwide, with 1.6 million deaths reported annually. Non-small cell lung cancer (NSCLC) represents 85% of all lung cancer cases and carries a poor 5-year survival rate below 15%. Prognoses remain dismal due to the large number of patients diagnosed with advanced stage disease and the development of resistance to current therapies. A better understanding of acquired drug resistance will help to circumvent the progression of lung cancer and make significant strides in improving NSCLC patient treatment. Our recent work demonstrates that dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) and its amino-terminally truncated splice variant (t-DARPP) promote lung tumor growth in orthotopic mouse models. IHC staining of 62 human lung adenocarcinoma tissues showed that t-DARPP expression is elevated with increasing tumor (T) staging score, which represents the size of the primary tumor and whether it has grown into nearby areas, as a metric of tumor progression and growth. Correspondingly, a computational biology analysis of 513 lung adenocarcinoma patients revealed upregulation of t-DARPP isoform expression correlates with advanced T stage and is associated with poor overall survival. We identified a novel physical interaction between DARPP-32 and inhibitory kappa B kinase-α (IKKα) that promotes NSCLC cell migration through activation of non-canonical NF-κB2 signaling. It has been shown that DARPP-32 overexpression inhibits gefitinib-induced apoptosis in gastric cancer and t-DARPP contributes to the trastuzumab resistance phenotype in breast cancer. Our recent findings suggest DARPP-32 and t-DARPP overexpression in NSCLC promotes resistance to specific molecular targeted inhibitors by enabling tumor cells to evade apoptosis via Akt- and Erk-dependent cell survival mechanisms. Current ongoing studies are focused on manipulating expression of DARPP-32 isoforms in lung tumor cells to prevent resistance to targeted therapies in NSCLC patients. Citation Format: SK Kayum Alam, Matteo Astone, Ping Liu, Li Wang, Abbygail M. Coyle, Erin N. Dankert, Dane K. Hoffman, Stephanie R. Hall, Wei Zhang, Rui Kuang, Anja C. Roden, Aaron S. Mansfield, Luke H. Hoeppner. Molecular mechanisms of non-small cell lung cancer growth and drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 873.