UCP2 Overexpression Redirects Glucose into Anabolic Metabolic Pathways.

Uncoupling protein 2 (UCP2) is often upregulated in cancer cells. The UCP2 upregulation is positively correlated with enhanced proliferation, tumorigenesis, and metabolic alterations, thus suggesting that UCP2 upregulation can play a key role in sensing metabolic changes to promote tumorigenesis. To determine the global metabolic impact of UCP2 upregulation, 13 C6 glucose as a source molecule is used to "trace" the metabolic fate of carbon atoms derived from glucose. UCP2 overexpression in skin epidermal cells enhances the incorporation of 13 C label to pyruvate, tricarboxylic acid cycle intermediates, nucleotides, and amino acids, suggesting that UCP2 upregulation reprograms cellular metabolism toward macromolecule synthesis. To the best of our knowledge, this is the first study to bring to light the overall metabolic differences caused by UCP2 upregulation.

Next-Gen Therapeutics for Skin Cancer: Nutraceuticals.

Growing modernization and lifestyle changes with limited physical activity have impacted diet and health, leading to an increased cancer mortality rate worldwide. As a result, there is a greater need than before to develop safe and novel anticancer drugs. Current treatment options such as chemotherapy, radiotherapy and surgery, induce unintended side effects, compromising patient's quality of life, and physical well-being. Therefore, there has been an increased global interest in the use of dietary supplements and traditional herbal medicines for treatment of cancer. Recently, nutraceuticals or "natural" substances isolated from food have attracted considerable attention in the cancer field. Emerging research suggests that nutraceuticals may indeed prevent and protect against cancer. The intent of this article is to review some of the current spice-derived nutraceuticals in the treatment of melanoma and skin cancer.

UCP2 upregulation promotes PLCγ-1 signaling during skin cell transformation.

Uncoupling protein 2 (UCP2), whose physiological role is to decrease mitochondrial membrane potential and reactive oxygen species (ROS) production, is often overexpressed in human cancers. UCP2 upregulation has recently been proposed as a novel survival mechanism for cancer cells. However, until now, how exactly UCP2 promotes tumorigenesis remains inconclusive. Based on a widely used skin cell transformation model, our data demonstrated that UCP2 differentially regulated ROS. UCP2 upregulation decreased superoxide whereas it increased hydrogen peroxide production with concomitant increase in the expression and activity of manganese superoxide dismutase (MnSOD), the primary mitochondrial antioxidant enzyme. Furthermore, hydrogen peroxide was responsible for induction of lipid peroxidation, and PLCγ-1 activation in UCP2 overexpressed cells. Additionally, PLCγ-1 activation enhanced skin cell transformation, and pharmacological, and siRNA mediated inhibition of PLCγ-1, markedly reduced colony formation, and 3D cell growth. Moreover, hydrogen peroxide scavenger, catalase, suppressed lipid peroxidation, and dampened PLCγ-1 activity. Taken together, our data suggest that (i) UCP2 is an important regulator of mitochondrial redox status and lipid signaling; (ii) hydrogen peroxide might mediate UCP2's tumor promoting activity; and (iii) pharmacological disruption of PLCγ-1 and/or hydrogen peroxide may have clinical utility for UCP2 overexpressed cancers.

Enzymatic activation of pyruvate kinase increases cytosolic oxaloacetate to inhibit the Warburg effect.

Pharmacological activation of the glycolytic enzyme PKM2 or expression of the constitutively active PKM1 isoform in cancer cells results in decreased lactate production, a phenomenon known as the PKM2 paradox in the Warburg effect. Here we show that oxaloacetate (OAA) is a competitive inhibitor of human lactate dehydrogenase A (LDHA) and that elevated PKM2 activity increases de novo synthesis of OAA through glutaminolysis, thereby inhibiting LDHA in cancer cells. We also show that replacement of human LDHA with rabbit LDHA, which is relatively resistant to OAA inhibition, eliminated the paradoxical correlation between the elevated PKM2 activity and the decreased lactate concentration in cancer cells treated with a PKM2 activator. Furthermore, rabbit LDHA-expressing tumours, compared to human LDHA-expressing tumours in mice, displayed resistance to the PKM2 activator. These findings describe a mechanistic explanation for the PKM2 paradox by showing that OAA accumulates and inhibits LDHA following PKM2 activation.

Enzymatic and metabolic regulation of lysine succinylation.

Lysine succinylation (Ksucc), defined as a transfer of a succinyl group to a lysine residue of a protein, is a newly identified protein post-translational modification1-3. This chemical modification is reversible, dynamic, and evolutionarily conserved 4 where it has been comprehensively studied in both bacterial and mammalian cells5-7. Numerous proteins involved in the regulation of various cellular and biological processes have been shown to be heavily succinylated5-7. Emerging clinical data provides evidence that dysregulation of Ksucc is correlated with the development of several diseases, including cardiovascular diseases and cancer7-9. Therefore, an in-depth understanding of Ksucc and its regulation is important not only for understanding its physiological function but also for developing drug therapies and targeted agents for these diseases. In this review, we highlight some of the recent advances in understanding the role of Ksucc and desuccinylation under physiological and pathological conditions.

Mitochondria in skin health, aging, and disease.

The skin is a high turnover organ, and its constant renewal depends on the rapid proliferation of its progenitor cells. The energy requirement for these metabolically active cells is met by mitochondrial respiration, an ATP generating process driven by a series of protein complexes collectively known as the electron transport chain (ETC) that is located on the inner membrane of the mitochondria. However, reactive oxygen species (ROS) like superoxide, singlet oxygen, peroxides are inevitably produced during respiration and disrupt macromolecular and cellular structures if not quenched by the antioxidant system. The oxidative damage caused by mitochondrial ROS production has been established as the molecular basis of multiple pathophysiological conditions, including aging and cancer. Not surprisingly, the mitochondria are the primary organelle affected during chronological and UV-induced skin aging, the phenotypic manifestations of which are the direct consequence of mitochondrial dysfunction. Also, deletions and other aberrations in the mitochondrial DNA (mtDNA) are frequent in photo-aged skin and skin cancer lesions. Recent studies have revealed a more innate role of the mitochondria in maintaining skin homeostasis and pigmentation, which are affected when the essential mitochondrial functions are impaired. Some common and rare skin disorders have a mitochondrial involvement and include dermal manifestations of primary mitochondrial diseases as well as congenital skin diseases caused by damaged mitochondria. With studies increasingly supporting the close association between mitochondria and skin health, its therapeutic targeting in the skin-either via an ATP production boost or free radical scavenging-has gained attention from clinicians and aestheticians alike. Numerous bioactive compounds have been identified that improve mitochondrial functions and have proved effective against aged and diseased skin. In this review, we discuss the essential role of mitochondria in regulating normal and abnormal skin physiology and the possibility of targeting this organelle in various skin disorders.

Reductive amination of α-Ketoglutarate in metabolite extracts results in glutamate overestimation.

Artifacts due to metabolite extraction, derivatization, and detection techniques can result in aberrant observations that are not accurate representations of actual cell metabolism. Here, we show that α-ketoglutarate (α-KG) is reductively aminated to glutamate in methanol:water metabolite extracts, which introduces an artifact into metabolomics studies. We also identify pyridoxamine and urea as amine donors for α-KG to produce glutamate in methanol:water buffer in vitro, and we demonstrate that the addition of ninhydrin to the methanol:water buffer suppresses the reductive amination of α-KG to glutamate in vitro and in metabolite extracts. Finally, we calculate that glutamate levels have been overestimated by 10-50%, depending on cell line, due to α-KG reductive amination. These findings suggest that precautions to account for α-KG reductive amination should be taken for the accurate quantification of glutamate in metabolomics studies.

Dysregulated metabolic enzymes and metabolic reprogramming in cancer cells.

Tumor cells carry various genetic and metabolic alterations, which directly contribute to their growth and malignancy. Links between metabolism and cancer are multifaceted. Metabolic reprogramming, such as enhanced aerobic glycolysis, mutations in the tricarboxylic acid (TCA) cycle metabolic enzymes, and dependence on lipid and glutamine metabolism are key characteristics of cancer cells. Understanding these metabolic alterations is crucial for development of novel anti-cancer therapeutic strategies. In the present review, the broad importance of metabolism in tumor biology is discussed, and the current knowledge on dysregulated metabolic enzymes involved in the vital regulatory steps of glycolysis, the TCA cycle, the pentose phosphate pathway, and lipid, amino acid, and mitochondrial metabolism pathways are reviewed.

Uncoupling protein 2 and metabolic diseases.

Mitochondria are fascinating organelles involved in various cellular-metabolic activities that are integral for mammalian development. Although they perform diverse, yet interconnected functions, mitochondria are remarkably regulated by complex signaling networks. Therefore, it is not surprising that mitochondrial dysfunction is involved in plethora of diseases, including neurodegenerative and metabolic disorders. One of the many factors that lead to mitochondrial-associated metabolic diseases is the uncoupling protein-2, a family of mitochondrial anion proteins present in the inner mitochondrial membrane. Since their discovery, uncoupling proteins have attracted considerable attention due to their involvement in mitochondrial-mediated oxidative stress and energy metabolism. This review attempts to provide a summary of recent developments in the field of uncoupling protein 2 relating to mitochondrial associated metabolic diseases.

UCP2 overexpression enhanced glycolysis via activation of PFKFB2 during skin cell transformation.

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane transporter which is often upregulated in human cancers. However, how this anion transporter affects tumorigenesis is not well understood. Using the skin cell transformation JB6 model, we demonstrated that UCP2 overexpression activated phosphofructokinase 2/fructose-2,6-bisphosphatase 2 (PFKFB2), a key regulator of glycolysis. In conjunction, upregulation of PFKFB2 expression correlated with elevated fructose 2,6-bisphosphate (Fru-2,6-P2) levels, 6-phosphofructo-1-kinase (PFK-1) activity, glucose uptake, and lactate production. Inhibiting PFKFB2 expression suppressed UCP2-mediated skin cell transformation, decreased cell proliferation, and enhanced mitochondrial respiration, while dampening aerobic glycolysis. The AKT signaling pathway was activated in the UCP2 overexpressed cells; furthermore, the activated AKT signaling contributed to the activation of PFKFB2. Whereas AKT inactivation blocked PFKFB2 activation, suggesting that AKT activation is an important step in PFKFB2 activation. Collectively, our data suggest that UCP2 is a critical regulator of cellular metabolism during cell transformation. Our data also demonstrate a potentially novel mechanism to understand UCP2's tumor-promoting role, which is through the AKT-dependent activation of PFKFB2 and thereby, the metabolic shift to glycolysis (the Warburg effect).

Components of cancer metabolism and therapeutic interventions.

All forms of life share a common indispensible need of energy. The requirement of energy is necessary for an organism not only to survive but also to thrive. The metabolic activities in normal cells rely predominately on mitochondrial oxidative phophorylation for energy generation in the form of ATP. On the contrary, cancer cells predominately rely on glycolysis rather than oxidative phosphorylation. It is long believed that an impairment of mitochondrial oxidative phosphorylation is the cause of this glycolytic phenotype observed in cancers. However, studies in cancer metabolism have revealed that mitochondrial function in many cancers is intact. It has also been observed that cancers utilize various forms of metabolism. The various metabolic phenotypes that are employed by cancer cells have a common purpose, to balance macromolecular biosynthesis and sufficient ATP production in order to support the rapid proliferation rate characteristic of these aberrant cells. These metabolic pathways are attractive targets for possible therapeutic interventions and currently research is underway to meet this end. More importantly, normal cells have essentially the same metabolic requirements as cancer cells so finding an approach to target these metabolic pathways without incurring detrimental effects on normal tissues remains the challenge.