Background Osteosarcoma (OS) is the most common malignant bone tumor and has a poor prognosis. The potential involvement of circular RNAs (circRNAs) in OS progression remains unexplored. Here, we report that CircECE1, a circular RNA derived from human ECE1, plays a critical role in energy metabolism in OS. Methods The RIP chip sequence assay was performed to confirm CircECE1, through overexpression or knockdown of CircECE1 to verify its function in 143B and U2OS. RNA immunoprecipitation and immunoprecipitation were used to verify CircECE1’s regulation of protein c-Myc and co- immunoprecipitation was used to verified the competitive binding relationship between CircECE1 and SPOP. The influence of CircECE1 on energy metabolism was evaluated by seahorse experiment, western blot, and immunohistochemistry. Results We found that CircECE1 is highly expressed in OS tissues and cells and that CircECE1 knockdown suppresses tumor proliferation and metastasis both in vitro and in vivo. Further, CircECE1 significantly promotes glucose metabolism in OS cells in vitro and in vivo. Mechanistically, CircECE1 interacts with c-Myc to prevent speckle-type POZ-mediated c-Myc ubiquitination and degradation. C-Myc inhibits thioredoxin binding protein (TXNIP) transcription and subsequently activates the Warburg effect. Conclusions CircECE1 regulates the Warburg effect through the c-Myc/TXNIP axis. CircECE1 mediated signal transduction plays a important role in OS process and energy metabolism. These findings may identify novel targets for OS molecular therapy.

Two-stage culture was efficient in enhancing total ganoderic acid (GA) production by Ganoderma lucidum (Fang and Zhong, Biotechnol Prog 18:51-54, 2002). As different GAs have different bioactivities, it is critical to understand the kinetics of individual GA production during fermentation, but no related information is yet available. To understand the regulation of GA biosynthesis, investigation of the accumulation of intermediate (lanosterol) and by-product (ergosterol) and of the expression of three important biosynthetic genes was also conducted in liquid shaking and static cultures of G. lucidum. The results showed that the content of individual GAs increased rapidly in the liquid static culture, and their maximum value was 6- to 25-fold that of shaking culture while lanosterol content in the former was lower than the latter. The transcript of squalene synthase (SQS), lanosterol synthase and 3-hydroxy-3-methylglutaryl coenzyme A reductase in liquid static culture was 4.3-, 2.1-, and 1.9-fold that of the shaking culture, respectively. Higher GA content in liquid static culture was related to increased transcription of those genes especially SQS. The work is helpful to the production of individual GAs and provided an insight into why the liquid static culture was superior to the shaking culture in view of biosynthetic gene expression.

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Ganoderic acids produced by Ganoderma lucidum, a well-known traditional Chinese medicinal mushroom, exhibit antitumor and antimetastasis activities. Genetic modification of G. lucidum is difficult but critical for the enhancement of cellular accumulation of ganoderic acids. In this study, a homologous genetic transformation system for G. lucidum was developed for the first time using mutated sdhB, encoding the iron-sulfur protein subunit of succinate dehydrogenase, as a selection marker. The truncated G. lucidum gene encoding the catalytic domain of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) was overexpressed by using the Agrobacterium tumefaciens-mediated transformation system. The results showed that the mutated sdhB successfully conferred carboxin resistance upon transformation. Most of the integrated transfer DNA (T-DNA) appeared as a single copy in the genome. Moreover, deregulated constitutive overexpression of the HMGR gene led to a 2-fold increase in ganoderic acid content. It also increased the accumulation of intermediates (squalene and lanosterol) and the upregulation of downstream genes such as those of farnesyl pyrophosphate synthase, squalene synthase, and lanosterol synthase. This study demonstrates that transgenic basidiomycete G. lucidum is a promising system to achieve metabolic engineering of the ganoderic acid pathway.