MAIA, Fc receptor-like 3, supersedes JUNO as IZUMO1 receptor during human fertilization.

Gamete fusion is a critical event of mammalian fertilization. A random one-bead one-compound combinatorial peptide library represented synthetic human egg mimics and identified a previously unidentified ligand as Fc receptor-like 3, named MAIA after the mythological goddess intertwined with JUNO. This immunoglobulin super family receptor was expressed on human oolemma and played a major role during sperm-egg adhesion and fusion. MAIA forms a highly stable interaction with the known IZUMO1/JUNO sperm-egg complex, permitting specific gamete fusion. The complexity of the MAIA isotype may offer a cryptic sexual selection mechanism to avoid genetic incompatibility and achieve favorable fitness outcomes.

SMAD4 loss limits the vulnerability of pancreatic cancer cells to complex I inhibition via promotion of mitophagy.

Pancreatic cancer is one of the deadliest forms of cancer, which is attributed to lack of effective treatment options and drug resistance. Mitochondrial inhibitors have emerged as a promising class of anticancer drugs, and several inhibitors of the electron transport chain (ETC) are being clinically evaluated. We hypothesized that resistance to ETC inhibitors from the biguanide class could be induced by inactivation of SMAD4, an important tumor suppressor involved in transforming growth factor ß (TGFß) signaling, and associated with altered mitochondrial activity. Here we show that, paradoxically, both TGFß-treatment and the loss of SMAD4, a downstream member of TGFß signaling cascade, induce resistance to biguanides, decrease mitochondrial respiration, and fragment the mitochondrial network. Mechanistically, the resistance of SMAD4-deficient cells is mediated by increased mitophagic flux driven by MAPK/ERK signaling, whereas TGFß-induced resistance is autophagy-independent and linked to epithelial-to-mesenchymal transition (EMT). Interestingly, mitochondria-targeted tamoxifen, a complex I inhibitor under clinical trial, overcomes resistance mediated by SMAD4-deficiency or TGFß signaling. Our data point to differential mechanisms underlying the resistance to treatment in PDAC arising from TGFß signaling and SMAD4 loss, respectively. The findings will help the development of mitochondria-targeted therapy for pancreatic cancer patients with SMAD4 as a plausible predictive marker.

Dihydroorotate dehydrogenase in oxidative phosphorylation and cancer.

Dihydroorotate dehydrogenase (DHODH) is an enzyme of the de novo pyrimidine synthesis pathway that provides nucleotides for RNA/DNA synthesis essential for proliferation. In mammalian cells, DHODH is localized in mitochondria, linked to the respiratory chain via the coenzyme Q pool. Here we discuss the role of DHODH in the oxidative phosphorylation system and in the initiation and progression of cancer. We summarize recent findings on DHODH biology, the progress made in the development of new, specific inhibitors of DHODH intended for cancer therapy, and the mechanistic insights into the consequences of DHODH inhibition.

A simple indirect colorimetric assay for measuring mitochondrial energy metabolism based on uncoupling sensitivity.

PURPOSE: Cancer cells rapidly adjust their balance between glycolytic and mitochondrial ATP production in response to changes in their microenvironment and to treatments like radiation and chemotherapy. Reliable, simple, high throughput assays that measure the levels of mitochondrial energy metabolism in cells are useful determinants of treatment effects. Mitochondrial metabolism is routinely determined by measuring the rate of oxygen consumption (OCR). We have previously shown that indirect inhibition of plasma membrane electron transport (PMET) by the mitochondrial uncoupler, FCCP, may also be a reliable measure of mitochondrial energy metabolism. Here, we aimed to validate these earlier findings by exploring the relationship between stimulation of oxygen consumption by FCCP and inhibition of PMET. METHODS: We measured PMET by reduction of the cell impermeable tetrazolium salt WST-1/PMS. We characterised the effect of different growth conditions on the extent of PMET inhibition by FCCP. Next, we compared FCCP-mediated PMET inhibition with FCCP-mediated stimulation of OCR using the Seahorse XF96e flux analyser, in a panel of cancer cell lines. RESULTS: We found a strong inverse correlation between stimulation of OCR and PMET inhibition by FCCP. PMET and OCR were much more severely affected by FCCP in cells that rely on mitochondrial energy production than in cells with a more glycolytic phenotype. CONCLUSION: Indirect inhibition of PMET by FCCP is a reliable, simple and inexpensive high throughput assay to determine the level of mitochondrial energy metabolism in cancer cells.

Reactivation of Dihydroorotate Dehydrogenase-Driven Pyrimidine Biosynthesis Restores Tumor Growth of Respiration-Deficient Cancer Cells.

Cancer cells without mitochondrial DNA (mtDNA) do not form tumors unless they reconstitute oxidative phosphorylation (OXPHOS) by mitochondria acquired from host stroma. To understand why functional respiration is crucial for tumorigenesis, we used time-resolved analysis of tumor formation by mtDNA-depleted cells and genetic manipulations of OXPHOS. We show that pyrimidine biosynthesis dependent on respiration-linked dihydroorotate dehydrogenase (DHODH) is required to overcome cell-cycle arrest, while mitochondrial ATP generation is dispensable for tumorigenesis. Latent DHODH in mtDNA-deficient cells is fully activated with restoration of complex III/IV activity and coenzyme Q redox-cycling after mitochondrial transfer, or by introduction of an alternative oxidase. Further, deletion of DHODH interferes with tumor formation in cells with fully functional OXPHOS, while disruption of mitochondrial ATP synthase has little effect. Our results show that DHODH-driven pyrimidine biosynthesis is an essential pathway linking respiration to tumorigenesis, pointing to inhibitors of DHODH as potential anti-cancer agents.

Mitochondrial Targeting of Metformin Enhances Its Activity against Pancreatic Cancer.

Pancreatic cancer is one of the hardest-to-treat types of neoplastic diseases. Metformin, a widely prescribed drug against type 2 diabetes mellitus, is being trialed as an agent against pancreatic cancer, although its efficacy is low. With the idea of delivering metformin to its molecular target, the mitochondrial complex I (CI), we tagged the agent with the mitochondrial vector, triphenylphosphonium group. Mitochondrially targeted metformin (MitoMet) was found to kill a panel of pancreatic cancer cells three to four orders of magnitude more efficiently than found for the parental compound. Respiration assessment documented CI as the molecular target for MitoMet, which was corroborated by molecular modeling. MitoMet also efficiently suppressed pancreatic tumors in three mouse models. We propose that the novel mitochondrially targeted agent is clinically highly intriguing, and it has a potential to greatly improve the bleak prospects of patients with pancreatic cancer. Mol Cancer Ther; 15(12); 2875-86. ©2016 AACR.