This study aims to explore the biological actions of circular RNA (circRNA) ArfGAP with SH3 domain, ankyrin repeat and PH domain 2 (circ_ASAP2, circ_0006089) in cisplatin (DDP) resistance of gastric cancer. Circ_ASAP2, ecto-5′-nucleotidase (NT5E) and miR-330-3p were quantified by quantitative real-time PCR or western blot. The measurements of the IC 50 value and cell proliferation were done using 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. Cell colony formation, cell cycle distribution, apoptosis, migration and invasion were evaluated by the colony formation, flow cytometry and transwell assays. Dual-luciferase reporter assay was performed to confirm the targeted relationship between different molecules. The role of circ_ASAP2 in tumor growth was gauged by in vivo animal studies. Circ_ASAP2 and NT5E were overexpressed in DDPresistant gastric cancer tissues and cells. Knockdown of circ_ASAP2 promoted DDP sensitivity, apoptosis and repressed proliferation, migration and invasion of DDPresistant gastric cancer cells in vitro and diminished tumor growth in vivo. Moreover, NT5E was a downstream effector of circ_ASAP2 in regulating cell DDP sensitivity and functional behaviors. Mechanistically, circ_ASAP2 directly bound to miR-330-3p to promote NT5E expression. Furthermore, circ_ASAP2 modulated cell DDP sensitivity and functional behaviors by targeting miR-330-3p. Knockdown of circ_ASAP2 promoted DDP sensitivity and suppressed malignant behaviors of DDP-resistant gastric cancer cells through targeting the miR-330-3p/NT5E axis.

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Immunophilins were discovered as cellular receptors for immunosuppressive drugs: cyclosporine A and FK506. Cyclophilins (CYPs, receptors for cyclosporine A) and FK506-binding proteins (FKBPs, receptors for FK506) do not share sequence homology, but have a common feature of peptidyl-prolyl cis-trans isomerase (PPIase) activity that catalyzes the cis-trans conversion of X-Pro peptide bonds, a rate-limiting step in the process of protein folding. Immunophilins are widely present in organisms from bacteria and fungi, to animals and plants. Genomics studies revealed that plants possess the largest immunophilin family. However, the physiological function of plant immunophilins is poorly understood. In this review, starting with a brief introduction of the immunophilin family and the current knowledge about their physiological roles in diverse organisms, the recent advances in the elucidation of plant immunophilin's physiological roles, largely via functional genomics tools, are summarized here. Notably, a striking feature of plant immunophilins is that a large fraction is localized in the chloroplast. Recent studies reveal that chloroplast immunophilins play a central role in the assembly and maintenance of photosynthetic complexes.

Arabidopsis cyclophilin38 (CYP38) is a thylakoid lumen protein critial for PSII assembly and maintenance, and its C-terminal region serves as the target binding domain. We hypothesized that four conserved residues (R290, F294, Q372, and F374) in the C-terminal domain are critical for the structure and function of CYP38. In yeast two-hybrid and protein pull-down assays, CYP38s with single-sited mutations (R290A, F294A, Q372A, or F374A) did not interact with the CP47 E-loop as the wild-type CYP38. In contrast, CYP38 with the R290A/F294A/Q372A/F374A quadruple mutation could bind the CP47 E-loop. Gene transformation analysis showed that the quadruple mutation prevented CYP38 to efficiently complement the mutant phenotype of cyp38. The C-terminal domain half protein with the quadruple mutation, like the wild-type one, could interact with the N-terminal domain or the CP47 E-loop in vitro. The cyp38 plants expressing CYP38 with the quadruple mutation showed a similar BN-PAGE profile as cyp38, but distinct from the wild type. The CYP38 protein with the quadruple mutation associated with the thylakoid membrane less efficiently than the wild-type CYP38. We concluded that these four conserved residues are indispensable as changes of all these residues together resulted in a subtle conformational change of CYP38 and reduced its intramolecular N-C interaction and the ability to associate with the thylakoid membrane, thus impairing its function in chloroplast.

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