Background Circular RNA (circRNA) is a novel class noncoding RNA (ncRNA) that plays a critical role in various cancers, including prostate cancer (PCa). However, the clinical significance, biological function, and molecular mechanisms of circRNAs in prostate cancer remain to be elucidated. Methods A circRNA array was performed to identified the differentially expressed circRNAs. circPDE5A was identified as a novel circRNA which downregulated in clinical samples. Functionally, the in vitro and in vivo assays were applied to explore the role of circPDE5A in PCa metastasis. Mechanistically, the interaction between circPDE5A and WTAP was verified using RNA pulldown followed by mass spectrometry, RNA Immunoprecipitation (RIP) assays. m6A methylated RNA immunoprecipitation sequencing (MeRIP-seq) was then used to identified the downstream target of circPDE5A. Chromatin immunoprecipitation assay (ChIP) and dual-luciferase reporter assay were used to identified transcriptional factor which regulated circPDE5A expression. Results circPDE5A was identified downregulated in PCa tissues compared to adjacent normal tissue and was negatively correlated with gleason score of PCa patients. circPDE5A inhibits PCa cells migration and invasion both in vitro and in vivo. circPDE5A blocks the WTAP-dependent N6-methyladenisine (m6A) methylation of eukaryotic translation initiation factor 3c (EIF3C) mRNA by forming the circPDE5A-WTAP complex, and finally disrupts the translation of EIF3C. Moreover, the circPDE5A-dependent decrease in EIF3C expression inactivates the MAPK pathway and then restrains PCa progression. Conclusions Our findings demonstrate that FOXO4-mediated upregulation of circPDE5A controls PCa metastasis via the circPDE5A-WTAP-EIF3C-MAPK signaling pathway and could serve as a potential therapeutic targer for PCa.

A lipid droplet (LD) is an organelle that consists of a phospholipid monolayer and a neutral lipid core, with proteins embedded in or attached to its surface. Until recently, cancers had long been regarded as genetic disorders with the abnormal activation of oncogenes and inactivation of tumor suppressor genes before their quality of a metabolic disorder began to be recognized. The last decade has witnessed the recognition of several metabolic characteristics of cancer cells, among which one is the accumulation of lipid droplets; therefore, attention has been given to exploring the role of LDs in carcinomas. In addition, there has been a remarkable expansion in understanding the complexity of LD's function in cellular homeostasis, including but not limited to energy supply, endoplasmic reticulum (ER) stress and oxidative stress management, or lipotoxicity alleviation. Thus, lipid droplet-associated proteins, which to a great extent determine the dynamics of a lipid droplet, have attracted the interest of numerous cancer researchers and their potential as cancer diagnostic biomarkers and therapeutic targets has been affirmed by emerging evidence. In this review, we systematically summarize the critical role of LDs in cancer and then focus on four categories of lipid droplet-associated proteins having the most direct influence on LD biosynthesis (diacylglycerol acyltransferase 1 (DGAT1) and diacylglycerol acyltransferase 2 (DGAT2)), degradation (adipose triglyceride lipase (ATGL)), and two renowned protein families on the LD surface (perilipins and cell death-inducing DNA fragmentation factor alpha-like effectors (CIDEs)). In this way, we aim to highlight their important role in tumor progression and their potential in clinical applications.

Background Circular RNAs (circRNAs) have been reported to play a significant role in tumorigenesis. However, the detailed function of circRNA in prostate cancer (PCa) is still largely unknown. Methods We quantified circTFDP2 expression in PCa tissues and adjacent normal tissues using quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR). Colony formation, Cell Counting Kit‐8 (CCK‐8), flow cytometry, transwell, and in vivo progression and metastasis assays were applied to reveal the proliferation and metastatic abilities of circTFDP2 in PCa cells. Mass spectrometry, RNA pulldown, RNA‐immunoprecipitation (RIP), western blotting and immunofluorescence were used for the mechanistic studies. qRT‐PCR and RIP assays were used to explore the regulatory role of eIF4A3 in the biogenesis of circTFDP2. Finally, functional assays showed the effect of circTFDP2‐containing exosomes on PCa cell progression. Results circTFDP2 was upregulated in PCa tissues compared with adjacent normal tissues. Furthermore, high circTFDP2 expression was positively correlated with the Gleason score. Functionally, circTFDP2 promoted PCa cell proliferation and metastasis both in vivo and in vitro. Mechanistically, circTFDP2 interacted with poly(ADP‐ribose) polymerase 1 (PARP1) protein in its DNA‐binding domain to prevent it from active caspase‐3‐dependent cleavage, and finally relieved PCa cells from DNA damage. In addition, RNA‐binding protein eIF4A3 can interact with the flanking region of circTFDP2 and promote the biogenesis of circTFDP2. Moreover, exosome‐derived circTFDP2 promoted PCa cell progression. Conclusions In general, our study demonstrated that circTFDP2 promoted PCa cell progression through the PARP1/DNA damage axis, which may be a promising therapeutic target for PCa.