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

Abstract

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).

UCP2 Overexpression Redirects Glucose into Anabolic Metabolic Pathways

“…The increased levels of UCP2 have been linked to enhanced cell proliferation and tumorigenicity . Furthermore, our results showed that UCP2 overexpression promoted skin tumorigenesis via altering glucose and lipid metabolism, and the key regulators of metabolic processes . As such, UCP2 is thought to be a crucial player in the cascade of molecular and metabolic events associated with carcinogenesis.…”

“…Hence, it is interesting to speculate that the reduction in the rate of glucose consumption and net lactate generation in UCP2 overexpressing cells may be a result of lactic acidosis. A possible explanation is that UCP2 overexpressing cells were initially glycolytic, then, due to increased accumulation of lactate and acidification of medium, may have resulted in a corresponding decrease of glucose consumption and lactate generation. Nevertheless, further investigations are necessary to evaluate whether lactic acidosis is the cause of transition from the Warburg effect to a nonglycolytic mode observed in UCP2 overexpressing cells.…”

“…Murine skin epidermal cells (purchased from American Type Culture Collection, Manassas, VA) were the only well‐characterized skin cell model to study tumor promotion . Stable UCP2 overexpressing and control pCMV cells were generated as previously described . Briefly, JB6 P+ (CL‐41) cells were transfected with a human UCP2‐containing or an empty pCMV6 vector (purchased from OriGene, Rockville, MD; catalog number SC320879 and PS100001, respectively) and stable clones were established.…”

“…Therefore, to decipher the influence of UCP2 overexpression on cellular metabolism, we performed overall pathway analysis using the stable isotope‐resolved metabolomics (SIRM) approach . UCP2 overexpressing cells were generated by transfecting JB6 P+ cells with a human UCP2‐containing vector or an empty base vector (pCMV6) as described previously . UCP2 overexpressing and control pCMV cells were labeled with uniformly 13 C‐enriched glucose to “trace” the fate of carbon atoms derived from 13 C glucose.…”

UCP2 gene polymorphisms in obesity and diabetes, and the role of UCP2 in cancer

“…Using the same model, our group has also found that upregulated UCP2 enhances the signaling of PLCγ‐1 . In UCP2 overexpressing cells, the levels of superoxide are decreased, whereas that of hydrogen peroxide is increased, concomitantly with increased expression and activity levels of manganese superoxide dismutase.…”