Nuclear Pyruvate Kinase M2 (PKM2) Contributes to Phosphoserine Aminotransferase 1 (PSAT1)-Mediated Cell Migration in EGFR-Activated Lung Cancer Cells.

An elevated expression of phosphoserine aminotransferase 1 (PSAT1) has been observed in multiple tumor types and is associated with poorer clinical outcomes. Although PSAT1 is postulated to promote tumor growth through its enzymatic function within the serine synthesis pathway (SSP), its role in cancer progression has not been fully characterized. Here, we explore a putative non-canonical function of PSAT1 that contributes to lung tumor progression. Biochemical studies found that PSAT1 selectively interacts with pyruvate kinase M2 (PKM2). Amino acid mutations within a PKM2-unique region significantly reduced this interaction. While PSAT1 loss had no effect on cellular pyruvate kinase activity and PKM2 expression in non-small-cell lung cancer (NSCLC) cells, fractionation studies demonstrated that the silencing of PSAT1 in epidermal growth factor receptor (EGFR)-mutant PC9 or EGF-stimulated A549 cells decreased PKM2 nuclear translocation. Further, PSAT1 suppression abrogated cell migration in these two cell types whereas PSAT1 restoration or overexpression induced cell migration along with an elevated nuclear PKM2 expression. Lastly, the nuclear re-expression of the acetyl-mimetic mutant of PKM2 (K433Q), but not the wild-type, partially restored cell migration in PSAT1-silenced cells. Therefore, we conclude that, in response to EGFR activation, PSAT1 contributes to lung cancer cell migration, in part, by promoting nuclear PKM2 translocation.

CHRNA5 belongs to the secondary estrogen signaling network exhibiting prognostic significance in breast cancer.

PURPOSE: Cholinergic signals can be important modulators of cellular signaling in cancer. We recently have shown that knockdown of nicotinic acetylcholine receptor subunit alpha 5, CHRNA5, diminishes the proliferative potential of breast cancer cells. However, modulation of CHRNA5 expression in the context of estrogen signaling and its prognostic implications in breast cancer remained unexplored. METHODS: Meta-analyses of large breast cancer microarray cohorts were used to evaluate the association of CHRNA5 expression with estrogen (E2) treatment, estrogen receptor (ER) status and patient prognosis. The results were validated through RT-qPCR analyses of multiple E2 treated cell lines, CHRNA5 depleted MCF7 cells and across a breast cancer patient cDNA panel. We also calculated a predicted secondary (PS) score representing direct/indirect induction of gene expression by E2 based on a public dataset (GSE8597). Co-expression analysis was performed using a weighted gene co-expression network analysis (WGCNA) pipeline. Multiple other publicly available datasets such as CCLE, COSMIC and TCGA were also analyzed. RESULTS: Herein we found that CHRNA5 expression was induced by E2 in a dose- and time-dependent manner in breast cancer cell lines. ER- breast tumors exhibited higher CHRNA5 expression levels than ER+ tumors. Independent meta-analysis for survival outcome revealed that higher CHRNA5 expression was associated with a worse prognosis in untreated breast cancer patients. Furthermore, CHRNA5 and its co-expressed gene network emerged as secondarily induced targets of E2 stimulation. These targets were largely downregulated by exposure to CHRNA5 siRNA in MCF7 cells while the response of primary ESR1 targets was dependent on the direction of the PS-score. Moreover, primary and secondary target genes were uncoupled and clustered distinctly based on multiple public datasets. CONCLUSION: Our findings strongly associate increased expression of CHRNA5 and its co-expression network with secondary E2 signaling and a worse prognosis in breast cancer.

Selective loss of phosphoserine aminotransferase 1 (PSAT1) suppresses migration, invasion, and experimental metastasis in triple negative breast cancer.

Breast cancer is the second leading cause of cancer-related deaths among women and 90% of these mortalities can be attributed to progression to metastatic disease. In particular, triple negative breast cancer (TNBC) is extremely aggressive and frequently metastasizes to multiple organs. As TNBCs are categorized by their lack of hormone receptors, these tumors are very heterogeneous and are immune to most targeted therapies. Metabolic changes are observed in the majority of TNBC and a large proportion upregulate enzymes within the serine synthesis pathway, including phosphoserine aminotransferase 1 (PSAT1). In this report, we investigate the role of PSAT1 in migration and invasion potential in a subset of TNBC cell types. We found that the expression of PSAT1 increases with TNBC clinical grade. We also demonstrate that suppression of PSAT1 or phosphoglycerate dehydrogenase (PHGDH) does not negatively impact cell proliferation in TNBC cells that are not dependent on de novo serine synthesis. However, we observed that suppression of PSAT1 specifically alters the F-actin cytoskeletal arrangement and morphology in these TNBC cell lines. In addition, suppression of PSAT1 inhibits motility and migration in these TNBC cell lines, which is not recapitulated upon loss of PHGDH. PSAT1 silencing also reduced the number of lung tumor nodules in a model of experimental metastasis; yet did not decrease anchorage-independent growth. Together, these results suggest that PSAT1 functions to drive migratory potential in promoting metastasis in select TNBC cells independent of its role in serine synthesis.