Tristetraprolin disables prostate cancer maintenance by impairing proliferation and metabolic function.

Tristetraprolin (TTP) is an RNA-binding protein that post-transcriptionally suppresses gene expression by delivering mRNA cargo to processing bodies (P-bodies) where the mRNA is degraded. TTP functions as a tumor suppressor in a mouse model of B cell lymphoma, and in some human malignancies low TTP expression correlates with reduced survival. Here we report important prognostic and functional roles for TTP in human prostate cancer. First, gene expression analysis of prostate tumors revealed low TTP expression correlates with patients having high-risk Gleason scores and increased biochemical recurrence. Second, in prostate cancer cells with low levels of endogenous TTP, inducible TTP expression inhibits their growth and proliferation, as well as their clonogenic growth. Third, TTP functions as a tumor suppressor in prostate cancer, as forced TTP expression markedly impairs the tumorigenic potential of prostate cancer cells in a mouse xenograft model. Finally, pathway analysis of gene expression data suggested metabolism is altered by TTP expression in prostate tumor cells, and metabolic analyses revealed that such processes are impaired by TTP, including mitochondrial respiration. Collectively, these findings suggest that TTP is an important prognostic indicator for prostate cancer, and augmenting TTP function would effectively disable the metabolism and proliferation of aggressive prostate tumors.

Lactate Wreaks Havoc on Tumor-Infiltrating T and NK Cells.

Both cancer cells and activated T and NK immune cells display enhanced nutrient uptake and metabolism characteristic of the Warburg phenotype. In this issue of Cell Metabolism, Brand et al. (2016) demonstrate that cancer cell LDHA-derived lactic acid selectively disables T and NK cell activation and tumor immune surveillance.

Blocking lactate export by inhibiting the Myc target MCT1 Disables glycolysis and glutathione synthesis.

Myc oncoproteins induce genes driving aerobic glycolysis, including lactate dehydrogenase-A that generates lactate. Here, we report that Myc controls transcription of the lactate transporter SLC16A1/MCT1 and that elevated MCT1 levels are manifest in premalignant and neoplastic Eµ-Myc transgenic B cells and in human malignancies with MYC or MYCN involvement. Notably, disrupting MCT1 function leads to an accumulation of intracellular lactate that rapidly disables tumor cell growth and glycolysis, provoking marked alterations in glycolytic intermediates, reductions in glucose transport, and in levels of ATP, NADPH, and ultimately, glutathione (GSH). Reductions in GSH then lead to increases in hydrogen peroxide, mitochondrial damage, and ultimately, cell death. Finally, forcing glycolysis by metformin treatment augments this response and the efficacy of MCT1 inhibitors, suggesting an attractive combination therapy for MYC/MCT1-expressing malignancies.

Synthesis of C11-Desmethoxy Soraphen A1α: A natural product analog that inhibits acetyl-CoA carboxylase.

A synthesis of C11-desmethoxy soraphen A1α is described that proceeds in just 14 steps from readily available starting materials. This natural product analog was identified as a target of interest in a program aimed at identifying novel natural product-inspired inhibitors of acetyl-CoA carboxylase (ACC) as potential anticancer therapeutics. While describing the most efficient synthesis of a soraphen A1α analog (total syntheses of the natural product have been reported that proceed in 25 to ≥40 linear steps), we also present data supporting the conclusion that C11-heteroatom functionality is a beneficial but unnecessary structural characteristic of soraphen A1α analogs for inhibiting ACC.

Metabolic regulation of invadopodia and invasion by acetyl-CoA carboxylase 1 and de novo lipogenesis.

Invadopodia are membrane protrusions that facilitate matrix degradation and cellular invasion. Although lipids have been implicated in several aspects of invadopodia formation, the contributions of de novo fatty acid synthesis and lipogenesis have not been defined. Inhibition of acetyl-CoA carboxylase 1 (ACC1), the committed step of fatty acid synthesis, reduced invadopodia formation in Src-transformed 3T3 (3T3-Src) cells, and also decreased the ability to degrade gelatin. Inhibition of fatty acid synthesis through AMP-activated kinase (AMPK) activation and ACC phosphorylation also decreased invadopodia incidence. The addition of exogenous 16∶0 and 18∶1 fatty acid, products of de novo fatty acid synthesis, restored invadopodia and gelatin degradation to cells with decreased ACC1 activity. Pharmacological inhibition of ACC also altered the phospholipid profile of 3T3-Src cells, with the majority of changes occurring in the phosphatidylcholine (PC) species. Exogenous supplementation with the most abundant PC species, 34∶1 PC, restored invadopodia incidence, the ability to degrade gelatin and the ability to invade through matrigel to cells deficient in ACC1 activity. On the other hand, 30∶0 PC did not restore invadopodia and 36∶2 PC only restored invadopodia incidence and gelatin degradation, but not cellular invasion through matrigel. Pharmacological inhibition of ACC also reduced the ability of MDA-MB-231 breast, Snb19 glioblastoma, and PC-3 prostate cancer cells to invade through matrigel. Invasion of PC-3 cells through matrigel was also restored by 34∶1 PC supplementation. Collectively, the data elucidate the novel metabolic regulation of invadopodia and the invasive process by de novo fatty acid synthesis and lipogenesis.