title: Disruption of Proline Synthesis in Melanoma Inhibits Protein Production Mediated by the GCN2 Pathway.
abstract: Many processes are deregulated in melanoma cells and one of those is protein production. Although much is known about protein synthesis in cancer cells, effective ways of therapeutically targeting this process remain an understudied area of research. A process that is upregulated in melanoma compared with normal melanocytes is proline biosynthesis, which has been linked to both oncogene and tumor suppressor pathways, suggesting an important convergent point for therapeutic intervention. Therefore, an RNAi screen of a kinase library was undertaken, identifying aldehyde dehydrogenase 18 family, member A1 (ALDH18A1) as a critically important gene in regulating melanoma cell growth through proline biosynthesis. Inhibition of ALDH18A1, the gene encoding pyrroline-5-carboxylate synthase (P5CS), significantly decreased cultured melanoma cell viability and tumor growth. Knockdown of P5CS using siRNA had no effect on apoptosis, autophagy, or the cell cycle but cell-doubling time increased dramatically suggesting that there was a general slowdown in cellular metabolism. Mechanistically, targeting ALDH18A1 activated the serine/threonine protein kinase GCN2 (general control nonderepressible 2) to inhibit protein synthesis, which could be reversed with proline supplementation. Thus, targeting ALDH18A1 in melanoma can be used to disrupt proline biosynthesis to limit cell metabolism thereby increasing the cellular doubling time mediated through the GCN2 pathway.
  
  
  CONCLUSIONS
  This study demonstrates that melanoma cells are sensitive to disruption of proline synthesis and provides a proof-of-concept that the proline synthesis pathway can be therapeutically targeted in melanoma tumors for tumor inhibitory efficacy.
authors.affiliation: Department of Pharmacology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. The Melanoma and Skin Cancer Center, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. The Melanoma Therapeutics Program, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Kardos
authors.affiliation: Department of Pharmacology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Hannah C
authors.initials: HC
authors.lastname: Wastyk
authors.affiliation: Department of Pharmacology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. The Melanoma and Skin Cancer Center, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. The Melanoma Therapeutics Program, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. Department of Pathology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania. Department of Dermatology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania Department of Surgery, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania gprobertson@psu.edu.
authors.forename: Gavin P
authors.initials: GP
authors.lastname: Robertson
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000502:physiology; D005260:Female; D006801:Humans; D008544:Melanocytes / Q000378:metabolism; D008545:Melanoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000096:biosynthesis*; D011392:Proline / Q000096:biosynthesis*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D014162:Transfection
chemical_list: D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D011392:Proline; C000596432:ALDH18A1 protein, human; D000444:Aldehyde Dehydrogenase; C529271:EIF2AK4 protein, human; C070634:Eif2ak4 protein, mouse; D017346:Protein Serine-Threonine Kinases