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Mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) integrates various environmental signals to regulate cell growth and metabolism. DEPTOR, also termed DEPDC6, is an endogenous inhibitor of mTORC1 and mTORC2 activities. The abundance of DEPTOR centrally orchestrates the mTOR signaling network. However, the mechanisms by which DEPTOR stability is regulated are still elusive. Here, we report that OTU domain–containing ubiquitin aldehyde-binding protein 1 (OTUB1) specifically deubiquitinates DEPTOR in a deubiquitination assay. We found that OTUB1 directly interacted with DEPTOR via its N-terminal domain, deubiquitinated DEPTOR, and thereby stabilized DEPTOR in a Cys-91–independent but Asp-88–dependent manner, suggesting that OTUB1 targets DEPTOR for deubiquitination via a deubiquitinase activity–independent non-canonical mechanism. The interaction between OTUB1 and DEPTOR was enhanced when the cells were treated with amino acids. Moreover, OTUB1 suppressed amino acid–induced activation of mTORC1 in a DEPTOR-dependent manner and thereby ultimately controlled cellular autophagy, cell proliferation, and size. Our findings reveal a mechanism that stabilizes the mTORC1 inhibitor DEPTOR via OTUB1's deubiquitinase activity. Our insights may inform research into various mTOR activity–related diseases, such as cancer, and may contribute to the identification of new diagnostic markers and therapeutic strategies for cancer treatments.

FBW7, a key component of SCFFBW7 E3 ubiquitin ligase, targets various proteins for degradation via the conserved Cdc4 phosphodegron (CPD) in substrates. In this study, we report that KLF10 is degraded by FBW7 via a conserved CPD. Through systematic analysis of the degradation of KLF transcription factors by FBW7, we identified KLF10 as a novel degradation target of FBW7. Ectopic expression of FBW7 markedly promoted the degradation of KLF10 while knockdown of endogenous FBW7 increased the protein levels of KLF10. In addition, simultaneous mutations of both threonine 82 (T82) and serine 86 (S86) significantly reduced the FBW7-mediated KLF10 degradation. Moreover, KLF10 containing a conserved putative CPD (TPPXSP) from amino acids 82 to 87, directly interacted with WD40 domain of FBW7 in a phosphorylation-dependent manner. Importantly, FBW7 could reverse the KLF10-mediated inhibition of Smad7 activity. Thus, our study uncovers a novel regulatory mechanism underlying which KLF10 stability and its biological function are mediated by FBW7.

Dragon fruit, a kind of fruit belonging to Hylocereus spp., has brought about interest in China not only due to its important economic value with high contents of nutrients, but also due to the striking tolerance to drought stress. Fifteen morphological traits and 111 Inter-Simple Sequence Repeat (ISSR) markers generated from 16 primers were firstly employed to discriminate 50 accessions recently selected in China, as well as to evaluate their genetic relatedness. According to univariate statistical analysis of morphological traits, high variations were observed between or/and within the wild and cultivated lines. The dendrogram of 50 accessions was constructed based on morphological traits. Taking 7.50 as a threshold, three major clusters could be observed, i.e. the first included nine genotypes, which mainly belonged to wild accessions; the second clusters standing for the red pulp genotypes; the third consisting of the white pulp accessions. Each ISSR primer generated 4–10 obvious DNA bands ranging from 100 bp to 1500 bp, with the average of 6.9 per primer. The percentage of polymorphic bands (PPB) varied from 25.00% to 100% with an average of 66.12%, and DNA markers generated from primers UBC824, UBC891and UBC900 could efficiently fingerprint 50 genotypes. Polymorphism information content (PIC) among the tested genotypes varied from 0.49 to 0.93 with an average of 0.85, suggesting a high genetic diversity among the tested genotypes. Based on UPGMA method, 50 genotypes could be grouped into two major clusters at a genetic distance of 0.23. Although there existed discrepancy in genetic relatedness between morphological and ISSR loci, a significant correlation between the data of two evaluation methods was observed using Mantel correspondence test.

Abiotic stresses usually cause H2O2 accumulation, with harmful effects, in plants. Catalase may play a key protective role in plant cells by detoxifying this excess H2O2. Pitaya (Hylocereus undatus) shows broad ecological adaptation due to its high tolerance to abiotic stresses, e.g. drought, heat and poor soil. However, involvement of the pitaya catalase gene (HuCAT) in tolerance to abiotic stresses is unknown. In the present study, a full-length HuCAT3 cDNA (1870 bp) was isolated from pitaya based on our previous microarray data and RACE method. The cDNA sequence and deduced amino acid sequence shared 73-77% and 75-80% identity with other plant catalases, respectively. HuCAT3 contains conserved catalase family domain and catalytic sites. Pairwise comparison and phylogenetic analysis indicated that HuCAT3 is most similar to Eriobotrya japonica CAT, followed by Dimocarpus longan CAT and Nicotiana tabacum CAT1. Expression profile analysis demonstrated that HuCAT3 is mainly expressed in green cotyledons and mature stems, and was regulated by H2O2, drought, cold and salt stress, whereas, its expression patterns and maximum expression levels varied with stress types. HuCAT activity increased as exposure to the tested stresses, and the fluctuation of HuCAT activity was consistent with HuCAT3 mRNA abundance (except for 0.5 days upon drought stress). HuCAT3 mRNA elevations and HuCAT activities changes under cold stress were also in conformity with the cold tolerances among the four genotypes. The obtained results confirmed a major role of HuCAT3 in abiotic stress response of pitaya. This may prove useful in understanding pitaya's high tolerance to abiotic stresses at molecular level.