Abstract 3563: Potential role for a phosphoserine aminotransferase 1 and pyruvate kinase M2 (PSAT1:PKM2) functional interaction in lung cancer cells

Cellular production of serine provides precursors for numerous anabolic reactions, particularly for proteins and nucleic acid synthesis and for one carbon metabolism, and this pathway has been demonstrated to be elevated in many different cancer types. In addition, metabolites within serine synthesis can stimulate other processes required for neoplastic growth, including glucose metabolism, specifically through the activation of the glycolytic enzyme pyruvate kinase M2 (PKM2). However, the complete mechanism by which serine biosynthesis facilitates metabolic or cellular changes necessary for tumor growth are unclear and is further confounded by the observation that suppression of serine biosynthetic enzymes disrupts tumorigenesis even in the presence of exogenous serine. Phosphoserine aminotransferase 1 (PSAT1), the second enzyme in serine synthesis, catalyzes the conversion of 3-phosphohydroxypyruvate to phosphoserine and increased expression correlates with poorer overall survival in lung cancer patients. In order to determine whether PSAT1 may contribute to lung cancer progression, PSAT1 expression was stably silenced in A549 and H358 lung cancer cells. Although a modest change in cell proliferation was observed upon PSAT1 knock-down compared to control, there was a robust decrease in soft-agar colony formation in both cell types. PSAT1 suppression was accompanied by distinct morphological changes and an increase in E-cadherin expression, suggesting a potential switch in the epithelial-mesenchymal transition (EMT), which underlies the metastatic potential of cancer cells. Accordingly, PSAT1 suppression resulted in a decrease in cellular motility as demonstrated through wound healing assays. To ascertain whether specific PSAT1 mediated protein:protein interactions may contribute to the pro-tumorigenic potential of serine metabolism, we performed GST-PSAT1 pull-down assays that revealed a potential direct association with PKM2, which was confirmed by co-immunoprecipitation. In vitro recombinant enzyme assays found that PSAT1 activates PKM2, but not PKM1 and, addition of serine or fructose-1,6-bisphosphate further activated PKM2, suggesting that PSAT1-dependent stimulation is distinct from other allosteric modulators. Lastly, based on in silico modeling, site-directed mutagenesis of PKM2 identified amino acid residues required for this protein interaction. Taken together, elucidating the functional role of PSAT1-PKM2 in lung cancer cells may yield valuable information about the relationship between serine-glucose metabolism and EMT transition in cancer cells and provide an additional therapeutic target for cancer treatment. Citation Format: Rumeysa B. Sit, Traci Kruer, James Bradley, Michael Merchant, John O. Trent, Brian F. Clem. Potential role for a phosphoserine aminotransferase 1 and pyruvate kinase M2 (PSAT1:PKM2) functional interaction in lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3563. doi:10.1158/1538-7445.AM2017-3563