Increased activity of the serine synthesis pathway (SSP) has been demonstrated in many types of cancer and can contribute to tumor growth by providing precursors for numerous anabolic reactions. Lung cancer, which is the leading cause of cancer deaths in the U.S., is one of several tumor types displaying increased expression of enzymes within the SSP, particularly PSAT1 (phosphoserine aminotransferase 1). Furthermore, increased PSAT1 expression correlates with poorer overall survival in lung cancer patients. Several previous studies have demonstrated a requirement for PSAT1 for NSCLC proliferation and lung cancer growth. Yet, understanding the complete mechanism by which PSAT1 promotes lung cancer progression requires further investigation, particularly as serine can be imported from the extracellular environment. Recent discoveries of the non-canonical functions of metabolic enzymes in tumorigenesis prompted us to explore a plausible additional function of PSAT1 that may be contributing to lung tumorigenesis. Therefore, we investigated potential PSAT1 protein-protein interactions via GST pulldown assay with mass spectrometry (MS). Among the identified peptides, PKM2 was chosen for further study due to its prior functional link to serine metabolism. In vitro co-immunoprecipitation data showed that PSAT1 interacted selectively with PKM2, but not PKM1 and site-directed mutagenesis analysis found the contribution of the PKM2-specific exon in the interaction. Although in vitro assays found that PSAT1 enhanced the kinase function of recombinant PKM2, depletion of PSAT1 by shRNA did not alter the pyruvate kinase activity and expression in NSCLC cells. Recent reports implicating EGF-induced nuclear PKM2 function in transcription led us to study the role of PSAT1 in nuclear localization of PKM2 in EGFR-activated lung cancer cells. Cell fractionation studies demonstrated that silencing of PSAT1 in EGFR-mutant PC9 or EGF-stimulated A549 cells decreased PKM2 nuclear translocation. Further, PSAT1 suppression abrogated cell migration in EGFR-mutant PC9 and EGF stimulated A549. To further elucidate the role of nuclear PKM2, we introduced PKM2 variants tagged with a nuclear localization signal (NLS) into PSAT1 silenced PC9 cells. We found that re-expression of NLS-PKM2 acetyl-mimetic mutant, but not wild-type, partially restored the cell migration in PSAT1 silenced PC9 cells. Taken together, our findings suggested that PSAT1 contributes to EGFR-driven lung cancer cell migration in part through promoting nuclear PKM2 translocation and function.

Citation Format: Rumeysa Biyik-Sit, Traci Kruer, Susan M. Dougherty, James Bradley, Michael L. Merchant, John O. Trent, Brian F. Clem. Nuclear Pyruvate Kinase M2 (PKM2) contributes to PSAT1-mediated cell migration in EGFR-activated lung cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4933.