ESR1 and breast cancer: Accordingly, we found that the abundance of glutamine (Figure 1I) (34), a required substrate for de novo purine biosynthesis, was higher in ERα-positive than ERα-negative BC cell lines and phosphoribosylglycinamide formyltransferase, phosphoribosylglycinamide synthetase, phosphoribosylaminoimidazole synthetase (GART) (Figure 1I) (34), the tripartite enzyme required for the second enzymatic step in the chain of reactions for purine production, was one of the 2 common metabolic proteins, which siRNA-based depletion reduces ERα levels and prevents the proliferation of MCF-7 and Y537S cells.