Asparagine synthetase and G-protein coupled estrogen receptor are critical responders to nutrient supply in KRAS mutant colorectal cancer

The nutrient status of the tumor microenvironment has major impacts on cell growth. Under nutrient depletion, asparagine synthetase (ASNS)-mediated asparagine production increases to sustain cell survival. G protein-coupled estrogen receptor-1 (GPER1) signaling converges via cAMP/PI3K/AKT with KRAS signaling to regulate ASNS expression. However, the role of GPER1 in CRC progression is still debated, and the effect of nutrient supply on both ASNS and GPER1 relative to KRAS genotype is not well understood. Here, we modeled a restricted nutrient supply by eliminating glutamine from growing cancer cells in a 3D spheroid model of human female SW48 KRAS wild-type (WT) and KRAS G12A mutant (MT) CRC cells, to examine effects on ASNS and GPER1 expression. Glutamine depletion significantly inhibited cell growth in both KRAS MT and WT cells; however, ASNS and GPER1 were upregulated in KRAS MT compared to WT cells. When nutrient supply was adequate, ASNS and GPER1 were not altered between cell lines. The impact of estradiol, a ligand for GPER1, was examined for any additional effects on cell growth. Under glutamine deplete conditions, estradiol decreased the growth of KRAS WT cells but had no effect on KRAS MT cells; estradiol had no additive or diminutive effect on the upregulation of ASNS or GPER1 between the cell lines. We further examined the association of GPER1 and ASNS levels with overall survival in a clinical colon cancer cohort of The Cancer Genome Atlas. Both high GPER1 and ASNS expression associated with poorer overall survival for females only in advanced stage tumors. These findings suggest that KRAS MT cells have mechanisms in place that respond to decreased nutrient supply, typically observed in advanced tumors, by increasing the expression of ASNS and GPER1 to drive cell growth. Furthermore, KRAS MT cells are resistant to the protective effects of estradiol under nutrient deplete conditions. ASNS and GPER1 may therefore be potential therapeutic targets that can be exploited to manage and control KRAS MT CRC.