Fig 2: Proposed models: a the redox regulation of the actin-bundling function of LPL and b–d the regulation of peripheral actin dynamics by spatial oxidation of LPL. a LPL bundles F-actin by sequential binding of ABD1 and ABD2 to adjacent actin filaments. The regulatory helix (RH) domain folds onto ABD2. H2O2 treatment leads to disulfide bridge formation between Cys101 (located at the RH) and Cys42 (located at the EF-hand module), thereby leading to dissociation of ABD2 or less efficient binding of ABD2 to F-actin. Red colored flags show the location of Cys42 and Cys101 on LPL. b Cell spreading through peripheral actin dynamics is halted by H2O2 treatment. After weak adherence, cells spread by forming actin-based cellular extrusions. Administration of exogenous ROS blocks cellular extrusion formation and cell spreading. c, d Enlarged cartoon of the boxed region in b. c Under control conditions, actin bundling by reduced LPL is involved in the formation of cellular extensions. d Under pro-oxidative conditions, the formation of actin bundles by LPL is prevented, impeding the formation of cellular extrusions. The color scale from light to dark green indicates the concentration gradient of TRX1. In the absence of antioxidant systems at such rapidly forming structures, the likelihood of protein oxidation is elevated

Fig 3: LPL-roGFP-Orp1 is spatially oxidized at protrusions of cells. a Intensity profiles of TRX1, LPL, and F-actin in untreated (left) and 50 µM H2O2-treated (right) MV3 wt LPL eGFP cells. MV3 LPL eGFP cells (green) that firmly adhered to poly-D-lysine-coated coverslips overnight were kept untreated or were treated with 50 µM H2O2 for 30 min. The samples were then fixed and stained for TRX1 (blue) and F-actin (red). The samples were imaged using a confocal microscope (n = 5). Scale bar = 10 µm; ×100 magnification. b Quantification of TRX1 in filopodia and cell bodies. At least 50 cells were analyzed from three independent experiments. The data are presented as the mean ± SEM (n = 3; ****p < 0.0001, ns nonsignificant). P-values were calculated by t-test. c Schematic diagram of the LPL-roGFP-Orp1 sensor. d Representative time-lapse images of MV3 LPL-roGFP-Orp1 cells. The upper panel shows F-actin (white), and the lower panel shows the oxidation state of the roGFP-Orp1 probe. The magnified area shows filopodial extensions. The color scale from dark blue to green and red indicates the oxidation state of the sensor. Ratio imaging was performed with a confocal microscope equipped with dual excitation features (n = 3). Scale bar = 10 µm; ×100 magnification. e Heat map showing the ratio of oxidized (excitation (Ex) 405 nm) to reduced (Ex 488 nm) roGFP-Orp1 in LPL-roGFP-Orp1-expressing cells in the absence of H2O2 (time-lapse imaging, t = 0 h, three independent experiments, n = 103 cells). Each lane represents a single cell. The color scale from blue to green and magenta indicates the oxidation state of the sensor in different cells

Fig 4: TRX1 regulates LPL oxidation in prostate cancer and melanoma cells. a Schematic representation of the reduction of oxidized LPL in control (wt) PC3 cells (left) and in TRX1 knockdown PC3 cells (right). b Immunoblots (upper panel) and flow cytometry histograms (lower panel) showing stable knockdown of TRX1 in PC3 cells. PC3 cells were transduced with TRX1-targeting shRNAs or control shRNAs (n = 5). c Immunoblot showing the TRX1 trapping of LPL and PRX1 in control and TRX1 knockdown PC3 cells. The trapping was performed as described. Shown are nonreducing gels (n = 4). d Immunoblots of TRX1 trapping of LPL and PRX1 in MV3 cells. MV3 cells stably expressing LPL-FLAG constructs were transfected with siTRX1 or control siRNA. Thereafter, trapping was performed as described (n = 3). e Immunoblot of TRX1 trapping of LPL and PRX1 upon inhibition of TRXR1 in PC3 cells with auranofin (n = 3). f PC3 cells and g wt LPL-FLAG-expressing MV3 cells were either kept untreated or were irradiated with 30 Gy or 60 Gy for 10 min. The cells were then subjected to TRX1 kinetic trapping (n = 3)

Fig 5: TRX1 trapping and differential alkylation of LPL Cys-Ala mutants. a Representative immunoblots (IB) showing trapping of LPL by TRX1 C35S upon H2O2 treatment. PC3 cells were kept untreated or were treated with 0.1 mM H2O2. Thereafter, the cells were lyzed, and the trapping reaction was performed using TRX1 C35S (the trapping mutant) or TRX1 C35C (wt). TRX1-bound complexes were purified by streptavidin affinity purification and analyzed by western blotting under reducing and nonreducing conditions. Lysates were used as controls, and the other lanes show the trapping by wt TRX1 or C35S TRX1 (n = 3). b Representative IB of the trapping of different LPL Cys-Ala mutants (n = 3). HEK293 cells were transiently transfected with Cys-Ala LPL mutants, and trapping was performed as described. Lysates of LPL-expressing cells were used as controls. c Representative IB of differential alkylation of recombinant wt LPL (n = 3). Recombinant LPL was directly used or was reduced using DTT prior to differential alkylation. Thereafter, the LPL was kept untreated or was treated with 0.1 mM H2O2 for 15 min. Following this step, the samples were subjected to differential alkylation. Then, the samples were run on 6% nonreducing or reducing SDS-polyacrylamide gels and immunoblotted for LPL (n = 4). d Representative IB of differential alkylation of recombinant wt, C42A and C101A LPL after pre-reduction with DTT (n = 3). The samples were prepared and immunoblotted for LPL. The red arrow indicates the upper band for the oxidized form of LPL, while the black arrows indicate the lower band for the reduced form of LPL. e TRX1 trapping in PC3 cells and f PBTs. The cells were treated with the indicated concentrations of H2O2 and subjected to TRX1 kinetic trapping. Representative IBs stained for LPL and PRX1 are shown (n = 3)