Folate depletion induces erythroid differentiation through perturbation of de novo purine synthesis
Folate, an essential vitamin, is a one-carbon acceptor and donor in key metabolic reactions. Erythroid cells harbor a unique sensitivity to folate deprivation, as revealed by the primary pathological manifestation of nutritional folate deprivation: megaloblastic anemia. To study this metabolic sensitivity, we applied mild folate depletion to human and mouse erythroid cell lines, and primary murine erythroid progenitors. We show that folate depletion induces early blockade of purine synthesis and accumulation of the purine synthesis intermediate and signaling molecule, AICAR, followed by enhanced heme metabolism, hemoglobin synthesis, and erythroid differentiation. This is phenocopied by inhibition of folate metabolism using the SHMT1/2 inhibitor - SHIN1, and by AICAR supplementation. Mechanistically, the metabolically-driven differentiation is independent of nucleotide sensing through mTORC1 and AMPK, and is instead mediated by protein kinase C (PKC). Our findings suggest that folate deprivation-induced premature differentiation of erythroid progenitor cells is a molecular etiology to folate-deficiency induced anemia. Overall design: We investigated the impact of folate depletion and one-carbon metabolism inhibiton on K562 and MEL cells. We cultured K562 and MEL cells in 2,000 nM folic acid or 100 nM folic acid, and in the presence of SHIN1 (1.25 uM) or AICAR (500 nM). We performed gene expression profiling analysis following 72 hours of culture in the indicated  treatment conditions.