| Description |
A frequent adaptation in the development of melanoma is the downregulation of argininosuccinate synthetase 1 (ASS1), the rate limiting enzyme in the production of the amino acid arginine from citrulline and aspartate. It is known that ASS1 is required for cells to proliferate in the absence of arginine. Consequently, depletion of arginine is being actively investigated as a potential therapy for the treatment of ASS1 deficient cancers. While clinical efforts to exploit this vulnerability have found some success, resistance can arise due to a tumor's ability to adapt to arginine depleted environments over time. Searching for treatments to pair with arginine starvation to kill cells prior to this adaptation, we generated ASS1 knockout cells using CRISPR/Cas9 and subsequently deprived them of arginine. Here we show that intracellular amino acids acutely accumulate in ASS1 knockout cells starved of arginine. We determined that general control nonderepressible 2 (GCN2) protein, which can detect amino acid scarcity within the cell, was necessary for this phenotype. GCN2 dependent amino acid accumulation was protective for cell viability upon arginine starvation. Separately, based on a functional genomics screen, the role of the polyamine transporter ATPase 13A3 (ATP13A3) and related pathways in the growth of ASS1 deficient cells was explored. We identified ornithine as having an important role in the growth of ASS1 deficient cells, but the molecular mechanism remains unclear. Understanding the mechanisms by which cells respond to amino acid deprivation and the metabolic pathways essential to the growth of ASS1 deficient cancers, as presented here, may reveal novel therapeutic targets for these tumors. |
