PS-341 (bortezomib), a proteasome inhibitor, has been approved for the treatment of multiple myeloma. Our previous work has shown that PS-341 induces death receptor 5 (DR5)-dependent apoptosis and enhances the TNF-related apoptosis-inducing ligand-induced apoptosis in human non-small cell lung cancer cells. However, the definite mechanism remains undefined. In the present study, we reveal that PKCd and RSK2 mediate PS-341-induced DR5 upregulation, involving coactivation of endoplasmic reticulum (ER) stress. We discovered that PS-341 activated ER stress through elevating the expression of BiP, p-eIF2a, IRE1a, ATF4, ATF3, and CCAAT/enhancer-binding protein homologous protein (CHOP). Further study showed that DR5 upregulation was dependent on ATF4, ATF3, and CHOP expression. Silencing either one of the ATF4, ATF3, and CHOP expression decreased DR5 upregulation and subsequent apoptosis. We determined that ATF4 regulated ATF3 and CHOP expression. Thereafter, ATF3 and CHOP formed a complex and regulated DR5 expression. In addition, we discovered that the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and RSK2 were elevated after PS-341 treatment and inhibition of their phosphorylation using MAP-ERK kinase 1/2 inhibitor decreased the DR5 level, indicating that ERK/RSK2 signaling is involved in DR5 upregulation. Furthermore, we detected the cleavage of PKCd, and the blockage of PKCd expression cut down DR5 upregulation and apoptosis. Importantly, knockdown of PKCd expression decreased the induction of ER stress and the phosphorylation of ERK1/2 and RSK2, suggesting that PKCd regulates DR5 expression through ERK/RSK2 signaling and ATF4-CHOP/ATF3 axis. Collectively, we show that PS-341 induces PKCd-dependent DR5 expression through activation of ERK/RSK2 and ER stress signaling pathway.

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BackgroundCFLARL, also known as c-FLIPL, is a critical anti-apoptotic protein that inhibits activation of caspase 8 in mammalian cells. Previous studies have shown that arginine 122 of CFLARL can be mono-methylated. However, the precise role of arginine methyltransferase of CFLARL remains unknown. PRMT5 and PRMT1, which are important members of the PRMT family, catalyze the transfer of methyl groups to the arginine of substrate proteins. PRMT5 can monomethylate or symmetrically dimethylate arginine residues, while PRMT1 can monomethylate or asymmetrically dimethylate arginine residues.MethodsLung cancer cells were cultured following the standard protocol and the cell lysates were prepared to detect the given proteins by Western Blot analysis, and the protein interaction was assayed by co-immunoprecipitation (Co-IP) or GST pull-down assay. CFLARL ubiquitination level was evaluated by proteasomal inhibitor treatment combined with HA-Ub transfection and WB assay. PRMT1 and PRMT5 genes were knocked down by siRNA technique.ResultsWe show that PRMT5 up-regulated the protein levels of CFLARL by decreasing the ubiquitination and increasing its protein level. Additionally, PRMT1 down-regulated the protein level of CFLARL by increasing the ubiquitination and degradation. The overexpression of PRMT5 can inhibit the interaction between CFLARL and ITCH, which has been identified as an E3 ubiquitin ligase of CFLARL, while overexpressed PRMT1 enhances the interaction between CFLARL and ITCH. Furthermore, we verified that dead mutations of PRMT5 or PRMT1 have the same effects on CFLARL as the wild-type ones have, suggesting it is the physical interaction between CFLAR and PRMT1/5 that regulates CFLARL degradation other than its enzymatic activity. Finally, we showed that PRMT5 and PRMT1 could suppress or facilitate apoptosis induced by doxorubicin or pemetrexed by affecting CFLARL in NSCLC cells.ConclusionsPRMT5 and PRMT1 mediate the distinct effects on CFLARL degradation by regulating the binding of E3 ligase ITCH in NSCLC cells. This study identifies a cell death mechanism that is fine-tuned by PRMT1/5 that modulate CFLARL degradation in human NSCLC cells.Electronic supplementary materialThe online version of this article (10.1186/s13046-019-1064-8) contains supplementary material, which is available to authorized users.

Hypovitaminosis D is highly prevalent in type 2 diabetes. The aim of this study is to determine the serum levels of 25-hydroxyvitamin D [25(OH)D] in type 2 diabetic patients with and without mild cognitive impairment (MCI), and examine the relationship of 25(OH)D and MCI with other clinical factors. One hundred and sixty-five diabetic patients were enrolled in this study. Among whom, 95 patients were considered as MCI [Montreal Cognitive Assessment score (MoCA) < 26] and the other 70 as no MCI (MoCA ≥ 26). Subjects were assessed clinically. Diabetic patients with MCI had a longer duration of DM, fewer years of education, elevated fasting blood glucose (FBG), resistant index (RI) of carotid, and lower levels of 25(OH)D {[17.35 (13.02-25.92) vs 28.00 (19.67-34.30)] ng/ml, P < 0.001}. The MoCA score was positively correlated with log10[25(OH)D], education year, and inversely correlated with duration of DM, history of hypertension, intima-media thickness (IMT), FBG, max-RI, and min-RI. Log10[25(OH)D] was positively correlated with MoCA score, and inversely correlated with IMT, in multivariate regression analysis adjusted for age, sex, and education year, 25(OH)D (β = 0.210, P = 0.003), history of hypertension (β = -0.191, P = 0.007), IMT (β = -0.194, P = 0.007), and FBG (β = -0.157, P = 0.026) independently predicted MoCA score. In conclusion, our results suggest that levels of serum 25(OH)D are inversely associated with the cognitive impairment in diabetic patients. Vitamin D may be a potential protective factor for cognitive impairment in patients with type 2 diabetes.

Treatment of N,N-bis(diphenylphosphanylmethyl)-3-aminopyridine (3-bdppmapy) with AgX (X = Br, I, CN, SCN, dicyanamide (dca)) under different reaction conditions afforded seven mononuclear, dinuclear, and polymeric coordination complexes including [Ag 4 I 4 (3-bdppmapynetwork in which chairlike [Ag 4 I 4 ] units are interconnected by μ 3 -3-bdppmapy bridges. Compounds 2 and 4 hold a similar centrosymmetric framework in which two [(3-bdppmapy)AgI] (2) or [(3-bdppmapy)Ag 2 (CN) 2 ] ( 4) units are linked by a μ-3-bdppmapy. Compound 3 has a batlike cationic structure in which two Ag/3bdppmapy units are joined by a pair of μ-Br and μ-3-bdppmapy bridges. Compounds 5 and 6 have a similar cationic mononuclear structure in which the Ag(I) center is chelated by two 3-bdppmapy ligands. Compound 7 possesses a 2D layer structure in which each one-dimensional (1D) chain [Ag 4 (dca) 4 (3-bdppmapy) 2 ] n is connected to its equivalent ones by μ 3 -dca bridges. Compound 1 as a representative example exhibited excellent catalytic activity toward the photodecomposition of a spectrum of 11 organic dyes in water under UV light irradiation and can be reused five times without noticeable decay of its catalytic efficiency.