Abstract
Glucose-6-phosphate dehydrogenase (G6PDH) is the rate-limiting enzyme in the pentose phosphate pathway (PPP) and plays a crucial role in the maintenance of redox homeostasis by producing nicotinamide adenine dinucleotide phosphate (NADPH), the major intracellular reductant. G6PDH has been shown to be a biomarker and potential therapeutic target for renal cell carcinoma (RCC). Here, we report a previously unknown biochemical mechanism through which caffeine, a well-known natural small molecule, regulates G6PDH activity to disrupt cellular redox homeostasis and suppress RCC development and progression. We found that caffeine can inhibit G6PDH enzymatic activity. Mechanistically, caffeine directly binds to G6PDH with high affinity (KD = 0.1923 μM) and competes with the coenzyme NADP+ for G6PDH binding, as demonstrated by the decreased binding affinities of G6PDH for its coenzyme and substrate. Molecular docking studies revealed that caffeine binds to G6PDH at the structural NADP+ binding site, and chemical cross-linking analysis demonstrated that caffeine inhibits the formation of dimeric G6PDH. G6PDH inhibition abrogated the inhibitory effects of caffeine on RCC cell growth. Moreover, inhibition of G6PDH activity by caffeine led to a reduction in the intracellular levels of NADPH and reactive oxygen species (ROS), and altered the expression of redox-related proteins in RCC cells. Accordingly, caffeine could inhibit tumor growth through inhibition of G6PDH activity in vivo. Taken together, these results demonstrated that caffeine can target G6PDH to disrupt redox homeostasis and inhibit RCC tumor growth, and has potential as a therapeutic agent for the treatment of RCC.
Highlights
Redox reactions represent a predominant and dynamic metabolic process that maintains human health (Ray et al, 2012)
We showed that caffeine can directly bind to glucose-6phosphate dehydrogenase (G6PDH) with high affinity and compete with NADP+ for G6PDH binding, which inhibits G6PDH activity, disrupts redox homeostasis, and leads to suppression of renal cell carcinoma (RCC) proliferation, both in vitro and in vivo
Given the structural similarity between caffeine and NADP+ and the important roles of NADP+ as a coenzyme for G6PDH enzymatic activity, we directly investigated whether caffeine influenced G6PDH-mediated enzymatic activity in vitro
Summary
Redox reactions represent a predominant and dynamic metabolic process that maintains human health (Ray et al, 2012). The PPP represents an alternative route for glycolysis for the dissimilation of carbohydrates, and is a major source of reducing power and metabolic intermediates for fatty acid and nucleic acid biosynthetic processes (Kotaka et al, 2005; Jiang et al, 2014). These biomasses produced through the PPP have an important role in cancer cell growth (Jiang et al, 2014). Emerging evidence from in vitro and in vivo studies has demonstrated that inhibition of the ratelimiting enzyme G6PDH in PPP can strongly suppress tumor cell growth (Mele et al, 2018), suggesting that G6PDH may be a potential therapeutic target for exploring effective cancer treatment modalities (Pandolfi et al, 1995; Zhang et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
