Fig 1: TRIB2 and PCBP2 reduce K48-ubiquitination of GPX4.a CHX chase experiments of GPX4 in the control and Bel-7402 cells with TRIB2 knocked out, with or without the simultaneous overexpression of PCBP2. The relative protein levels of GPX4 were normalized to those of GAPDH, and the “0 h” point was arbitrarily set to 100%. b TRIB2 and PCBP2 regulated GPX4 ubiquitination. GPX4 or its K48-ubiquitination and total-ubiquitination level in the WCL of Bel-7402 and SMMC-7721 cells with or without TRIB2 knockout in the presence or absence of ectopic expression of PCBP2. The K48-Ub and total-Ub of GPX4 were normalized to that of GPX4 in the GPX4-IPs by ImageJ and indicated below the blots. c PCBP2 acts as the downstream of TRIB2 to prevent the association between GPX4 and proteasome in Bel-7402 and SMMC-7721 cells. The relative GPX4 levels were normalized to PSMB3 in proteasome and normalized to GAPDH at WCL. The relative GPX4 levels were also calculated as the ratio between the one in proteasome and the one at WCL. Besides, the PSMB5 activity was also parallel examined at WCL. Data were analyzed by one-way ANOVA and expressed as mean ± SD. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. d, e The TRIB2 DQLVPD element and PCBP2 KH3 domain are critical to maintain GPX4 expression. GPX4 was measured by IB in the Bel-7402 cells transfected with the indicated plasmids. The relative GPX4 levels were normalized to that of GAPDH and indicated below the blots. f GPX4 in control and Bel-7402 cells with or without TRIB2 or PCBP2 knocked out in the presence or absence of overexpressed GPX4. The relative GPX4 levels were normalized to that of GAPDH and indicated below the blots. g Tumor growth in athymic mice inoculated with the same cells as shown in f. The weight and volume of a tumor are presented below the representative tumor image (n = 5/group); Scale bar = 3 mm. Data were analyzed by one-way ANOVA and expressed as mean ± SD. **P < 0.01; ****P < 0.0001. Images of all the immunoblots are representative of three independent experiments.
Fig 2: PSMB5 is a target of TRIB2 in the proteasome.a Schematic representation of the assembly and composition of the proteasome. b TRIB2 affected Ub levels independent of proteasome assembly. Ub levels were measured in the control, Bel-7402, and SMMC-7721 cells with or without TRIB2 knocked down and with or without POMP knocked down. c, d PSMB5 of 20S CP, but not 19S RP, was involved in the TRIB2-mediated effects on Ub level. Ub levels in the Bel-7402 and SMMC-7721 cells with or without TRIB2 knocked down and treated with DMSO, b-AP15 (5 µM, 24 h) (c), ZACD (100 µM, 24 h), TLCK (50 µM, 24 h), or BTZ (100 nM, 24 h) (d), as indicated. e PSMB5 was critical for TRIB2. Ub was measured in the Bel-7402 and SMMC-7721 cells with or without PSMB5 knocked out or compensatory PSMB5 expression, in the presence or absence of TRIB2 knockdown. f, g Ub at WCL and in proteasomes isolated from the Bel-7402 cells with TRIB2 knocked down or overexpressed, in the presence or absence of PSMB5. The samples derived from the same experiment using control beads had been processed in parallel. The levels of conj & poly Ub were normalized to that of GAPDH at WCL (f), while normalized to that of PSMB3 in the isolated proteasome (g). Images of all the immunoblots are representative of three independent experiments. The relative protein levels of the conj & poly Ub and mono Ub were normalized to those of GAPDH as calculated by ImageJ software and indicated just below the blots (b–f).
Fig 3: TRIB2 regulates Ub levels via the proteasome.a Ub in the control, Bel-7402 and SMMC-7721 cells with TRIB2 knocked down or overexpressed. b Schematic representation of Ub homeostasis. c CHX chase experiments of Ub in the control and Bel-7402 cells with TRIB2 knocked down. The relative protein levels of conj & poly and mono Ub were normalized to those of GAPDH, respectively, and the “0 h” point was arbitrarily set to 100%. d–f ALP did not participate in the regulation of Ub levels by TRIB2. Ub in the Bel-7402 cells with or without TRIB2 knocked down after treatment with the ALP inhibitors 3-MA (5 mM for 24 h) and CQ (20 µM, 24 h) (d), ATG5 knockout (e), or ATG7 knockdown (f). g Ub in the lysosomes isolated from the same cells as shown in a, as measured by IB. The relative protein levels of conj & poly Ub and mono Ub were normalized to those of LAMP2 as calculated by ImageJ software and indicated just below the blots. h, i TRIB2 did not regulate Ub levels through DUBs. Control and Bel-7402 cells with or without TRIB2 knocked down or overexpressed were treated with DMSO, VLX1570 (20 µM, 24 h), and EOAI (600 nM, 24 h), respectively (h), or in the presence or absence of UCH37 and USP14 knocked down (i). j, k TRIB2 regulated Ub levels via the proteasome. Ub levels at WCL (j) and in proteasome (k) were measured in the same cells shown in a and treated with DMSO or MG132 (8 µM, 12 h). The samples in k derive from the same experiment and the blots have been processed in parallel using control beads. The levels of conj & poly Ub were normalized to that of GAPDH at WCL (j), while normalized to that of PSMB3 in the isolated proteasome (k), and the data are graphed below the blots. Data were analyzed by one-way ANOVA and expressed as mean ± SD. ***P < 0.001; ****P < 0.0001. Images of all the immunoblots are representative of three independent experiments. The relative protein levels of the conj & poly Ub and mono Ub were normalized to those of GAPDH as calculated by ImageJ software and indicated just below the blots (a, d–f, h, i).
Supplier Page from Abcam for Anti-Proteasome 20S beta 3 antibody