Journal: Cell Death & Disease
Article Title: Both direct and indirect suppression of MCL1 synergizes with BCLXL inhibition in preclinical models of gastric cancer
doi: 10.1038/s41419-025-07481-8
Figure Lengend Snippet: A , B Role of ELK1, STAT3 and SRF in regulating the transcriptional activity of MCL1 under basal conditions and in response to HER2-targeting drugs. SNU-216 cells expressing empty vector or the indicated transcriptional factors were left untreated or treated with 100 ng/ml trastuzumab ( A ) or 200 nM lapatinib ( B ) for 72 h or 48 h, respectively. The levels of MCL1 mRNA were determined using RT-qPCR. C Effect of HER2-targeting drugs on STAT3 and SRF expression. SNU-216, NCI-N87 and GCIY were treated with 100 ng/ml trastuzumab or 200 nM lapatinib for 72 h or 48 h, respectively. The protein levels of p-STAT3, total STAT3, and SRF were determined by Western blotting. D , E Dual luciferase reporter assays to identify the binding site(s) of STAT3 and SRF in the MCL1 promoter. Left: diagram depicting the putative binding sites of STAT3 ( D ) or SRF ( E ) in the MCL1 promoter predicted by the JASPAR database. Right: Dual luciferase reporter assays conducted in HEK293T. F Reduced binding of STATS and SRF in the MCL1 promoter upon HER2-targeting drug treatments. SNU-216 cells were left untreated or treated with 100 ng/ml trastuzumab or 200 nM lapatinib for 72 h or 48 h, respectively. ChIP was conducted using specific antibodies against STAT3, SRF, and an IgG isotype control. G Co-IP analysis of the interaction of endogenous STAT3 and SRF in SNU-216 cells. H Direct interaction of exogenous STAT3 and SRF. HEK293T cells were transiently transfected with HA-tagged STAT3, Flag-tagged SRF, either individually or both. Equivalent lysates were immunoprecipitated with anti-HA or anti-Flag antibody and immunoblotted with the indicated antibodies. I Effect of overexpressing or deleting STAT3 on SRF expression. The mRNA (left) and protein (right) levels of SRF in SNU-216 cells with STAT3 overexpression or depletion were determined. J Similar experiments to those in panel I were conducted to detect the effect of manipulating SRF on STAT3 expression in SNU-216 cells. K Reduced binding of STAT3 in the SRF promoter upon HER2-targeting drug treatments. Similar experiments to those in ( F ) were conducted. L Depletion of STAT3 attenuated the binding of SRF in the MCL1 promoter. Similar experiments to those in ( F ) were performed in SNU-216 cells engineered to express sg STAT3 . ChIP was conducted at 72 h after addition of DOX to induce the deletion of STAT3 . 2 sgRNAs were tested. M , N Deleting STAT3 enhanced the sensitivity of GC lines to BCLXL inhibition. SNU-216 ( M ) and GCIY ( N ) cells inducibly expressing sg STAT3 or the sgRNA empty vector were treated with DOX alone, or in combination with indicated concentrations of BCLXLi. Cell viability was determined 48 h later. Two-way ANOVA was used for statistical significance. O STAT3 inhibitor synergized with BCLXLi in GC cell lines, regardless of their p-STAT3 levels. GC cell lines with high p-STAT3 levels (HGC-27, MKN45 and AGS) and the ones with low p-STAT3 levels (SNU-216, NCI-N87, GCIY) were treated with indicated concentrations of BCLXLi and STAT3 inhibitor and cell viability was determined 48 h later. Data in ( A ), ( B ), ( D ), ( E ), ( I , left ), ( J , left ), ( M – O ) represent the means ± SD of ≥3 independent experiments; data in panel ( C ), ( F – H ), ( I , right ), ( J , right ), ( K ) and ( L ) are representatives of 2 independent experiments.
Article Snippet: The GV492 lentiviral expression constructs of human ELK1, ELK3, ELK4, STAT3, SRF, as well as the GV366 (C-terminally HA-tagged) and GV657 (C-terminally Flag-tagged) constructs for transient expression of human STAT3 and SRF were purchased from Shanghai Genechem Co., Ltd.
Techniques: Activity Assay, Expressing, Plasmid Preparation, Quantitative RT-PCR, Western Blot, Luciferase, Binding Assay, Control, Co-Immunoprecipitation Assay, Transfection, Immunoprecipitation, Over Expression, Inhibition