Abstract 4686: Requirements of Gαi1 and Gαi3 for brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) induced PI3K/AKT and MAPK signaling as well as neuronal survival and migration

After the discovery of the involvement of neurotrophin receptor Trk (tropomyosin receptor kinase) in the biology of cancer, it is appreciated that inhibition of Trk activity is beneficial in the clinical oncology setting. The key intracellular mediators of activated Trk9s pro-survival and pro-metastatic signals are PI3K/AKT and MAPK (mitogen-activated protein kinases) signaling, which makes it extremely important to dissect the molecular mechanism and signaling components involved in Trk regulation of those signaling. Here we focus on the two inhibitory alpha subunits of heterotrimeric guanine nucleotide-binding proteins, Gαi1 and Gαi3, in Trk signaling. Gαi proteins are couple to cell surface receptors to convey extracellular messages to their effectors. Our previous study has indicated an unexpected and critical role of Gαi proteins in mediating receptor tyrosine kinase signaling (Cao et al., Science Signaling, 2009). Here we discovered a novel function of Gαi proteins in BDNF/NGF signaling. Gαi proteins are required for Brain-Derived Neurotrophic Factor (BDNF) and Nerve Growth Factor (NGF) to transduce signals from Trk receptor to stimulate MAPK (p38, JNK and ERK) and PI3K/AKT/mTORC1 signaling. Knockout of Gαi1 and Gαi3 completely blocked BDNF and NGF induced PI3K/AKT/mTORC1 and MAPK activation in MEFs (mouse embryonic fibroblasts). Both Gαi1 and Gαi3 associated with the Grb2-associated binding protein 1 (Gab1), and were required for the interaction of Gab1 with SHP2 as well as the interactions of Grb2 with SHP2, Shc, MEKK1 and MEKK2, in response to BDNF and NGF. Loss of Gαi1 and Gαi3 impaired the phosphorylation of Gab1, SHP2 and Shc in response to BDNF and NGF. Importantly, siRNA knockdown of both Gαi1 and Gαi3 inhibited BDNF and NGF induced AKT/mTORC1 and MAPK activation in cerebellar granule neuron, and BDNF induced neuronal survival, neuronal migration and neurite outgrowth were also largely impaired in cerebellar neurons with Gαi1 and Gαi3 deficiency. Notably, in mice brain tissues (both cortex and cerebellum); double knockout of Gαi1 and Gαi3 also totally abolished BDNF induced signaling. Overall, these results showed that Gαi1 and Gαi3 lie downstream of Trk receptor, but upstream of Gab1-Shc-Grb2-Shp2, mediating MAPK and PI3K/AKT/mTORC1 signaling as well neuronal survival and migration. We discovered for the first time that Gαi1 and Gαi3 proteins are novel players in Trk signaling, we support that therapeutic options can be developed by targeting these two new players as novel anti-tumor strategy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4686. doi:10.1158/1538-7445.AM2011-4686