SUMMARY A “switch” from oxidative phosphorylation (OXPHOS) to aerobic glycolysis is a hallmark of T cell activation and is thought to be required to meet the metabolic demands of proliferation. However, why proliferating cells adopt this less efficient metabolism, especially in an oxygen-replete environment, remains incompletely understood. We show here that aerobic glycolysis is specifically required for effector function in T cells but that this pathway is not necessary for proliferation or survival. When activated T cells are provided with costimulation and growth factors but are blocked from engaging glycolysis, their ability to produce IFN-γ is markedly compromised. This defect is translational and is regulated by the binding of the glycolysis enzyme GAPDH to AU-rich elements within the 3′ UTR of IFN-γ mRNA. GAPDH, by engaging/disengaging glycolysis and through fluctuations in its expression, controls effector cytokine production. Thus, aerobic glycolysis is a metabolically regulated signaling mechanism needed to control cellular function.

Nucleophosmin (NPM/B23) is a key regulator in the regulation of a number of processes including centrosome duplication, maintenance of genomic integrity, and ribosome biogenesis. While the mechanisms underlying NPM function are largely uncharacterized, NPM loss results in severe dysregulation of developmental and growth-related events. We show that NPM utilizes a conserved CRM1-dependent nuclear export sequence in its amino terminus to enable its shuttling between the nucleolus/nucleus and cytoplasm. In search of NPM trafficking targets, we biochemically purified NPM-bound protein complexes from HeLa cell lysates. Consistent with NPM's proposed role in ribosome biogenesis, we isolated ribosomal protein L5 (rpL5), a known chaperone for the 5S rRNA. Direct interaction of NPM with rpL5 mediated the colocalization of NPM with maturing nuclear 60S ribosomal subunits, as well as newly exported and assembled 80S ribosomes and polysomes. Inhibition of NPM shuttling or loss of NPM blocked the nuclear export of rpL5 and 5S rRNA, resulting in cell cycle arrest and demonstrating that NPM and its nuclear export provide a unique and necessary chaperoning activity to rpL5/5S.As the most prominent of subnuclear structures, the nucleolus has long been recognized as the site of active transcription of rRNA and ribosome assembly (8). Various nucleolar proteins, RNAs, and other factors have been implicated in the complex process of ribosome production and maturation (18). Recently, several groups reported the successful isolation and mapping of the mammalian nucleolar proteome (1, 2, 44). While these studies clearly identified proteins and ribonucleoproteins with purported roles in ribosome biogenesis, a surprising number of proteins within the nucleolar proteome (Ͼ100) have no known function. In previous decades, it was assumed that all nucleolar proteins must somehow contribute to static ribosome biogenesis simply by virtue of their localization. However, more-recent findings have demonstrated that the nucleolus is a dynamic subnuclear organelle which regulates numerous cellular processes, prompting a broadened view of the potential functions of nucleolar proteins (28).Nucleophosmin (NPM/B23) is an abundant phosphoprotein that resides within the granular regions of the nucleolus (46). Proliferating cells express NPM at high levels (9, 13), and NPM has been associated with a variety of cellular events, including ribosomal biogenesis, protein chaperoning, and centrosome duplication (13,23,35,36). Structurally, NPM is present in both monomeric and multimeric states, although NPM multimers appear predominant in the nucleolus and may be crucial for the assembly of maturing ribosomes (33,34,53). Furthermore, NPM, along with other nucleolar proteins, is believed (or has been shown) to actively mobilize into distinct subcellular pools, supporting the notion that NPM trafficking may be essential for its (proper) function (6). Indeed, NPM's transit from the nucleolus/nucleus is an essential event in S phase progression; when NPM export was...

Nucleophosmin (NPM) (B23) is an essential protein in mouse development and cell growth; however, it has been assigned numerous roles in very diverse cellular processes. Here, we present a unified mechanism for NPM's role in cell growth; NPM directs the nuclear export of both 40S and 60S ribosomal subunits. NPM interacts with rRNA and large and small ribosomal subunit proteins and also colocalizes with large and small ribosomal subunit proteins in the nucleolus, nucleus, and cytoplasm. The transduction of NPM shuttlingdefective mutants or the loss of Npm1 inhibited the nuclear export of both the 40S and 60S ribosomal subunits, reduced the available pool of cytoplasmic polysomes, and diminished overall protein synthesis without affecting rRNA processing or ribosome assembly. While the inhibition of NPM shuttling can block cellular proliferation, the dramatic effects on ribosome export occur prior to cell cycle inhibition. Modest increases in NPM expression amplified the export of newly synthesized rRNAs, resulting in increased rates of protein synthesis and indicating that NPM is rate limiting in this pathway. These results support the idea that NPM-regulated ribosome export is a fundamental process in cell growth.