Journal: The Journal of Biological Chemistry
Article Title: The receptor tyrosine kinase ErbB2/HER2 governs CDK4 inhibitor sensitivity, timing, and irreversibility of the G1/S transition
doi: 10.1016/j.jbc.2025.110865
Figure Lengend Snippet: High ErbB2 expression induces cell cycle arrest by repressing cyclin D1 expression via c-Myc under CDK4 inhibition. A and B , WT MCF-7 and ErbB2-overexpressing MCF-7 cells (high levels) were treated with CDK4i or DMSO 12 h after HRG stimulation and harvested 24 h after HRG stimulation. Western blotting of ( A ) p-ErbB2, p-RB (Ser807/811), p-RB (Thr373), RB, p-AKT (Thr308), AKT, p-ERK (Thr202/Thr204), ERK, c-Myc, cyclin D1, and p27 expression (in control cells, with DMSO treatment) after normalization with GAPDH expression ( B ). The data are displayed as the means ± SD. C - F , ErbB2-overexpressing cells (moderate) were individually treated with 250 nM CDK4i or DMSO (control) 12 h after stimulation with 10 nM HRG and fixed 16 h after stimulation with 10 nM HRG (CDK4i or DMSO addition 4 h later). Hsp90 and ErbB2 were coimmunostained. The scale bar represents 25 μm ( C ). Colocalization rate of Hsp90 and ErbB2 based on Mander’s tM1 and Pearson’s R values determined using Coloc 2 plugin of Image J; n = 10 ( D ). Hsp90 and PY100 were coimmunostained. The scale bar represents 25 μm ( E ). Colocalization rate of Hsp90 and PY100 based on Mander’s tM2 and Pearson’s R values; n = 10 ( F ). G and H , PLA signals detected in WT MCF-7 cells. Cells were individually treated with 250 nM CDK4i or DMSO (control) 12 h after stimulation with 10 nM HRG and fixed 16 h after stimulation with 10 nM HRG (CDK4i or DMSO addition 4 h later). PLA was performed using ErbB2 and Hsp90 antibodies. G , PLA signals detected in the presence of HER2 and Hsp90 antibodies ( left ). No signals detected after omitting Hsp90 antibody ( right ). The scale bar represents 100 μm. H , mean intensity of PLA signals per image was measured under each condition in ( G ) ( Left ). Number of nuclei per image was counted ( Right ). n = 59. I and J , FUCCI stably expressing MCF-7 cells were treated with CDK4i or DMSO (control) as well as 10 μM MG132, 12 h after stimulation with 10 nM HRG and collected 8 h later. I , ErbB2 and GAPDH expression determined by western blotting. ( J ) ErbB2 expression normalized to GAPDH expression; n = 3. The data are displayed as the means ± SD. K and L , ErbB2 cycloheximide pulse-chase assay was performed with FUCCI stably expressing MCF-7 cells. Cells were treated with CDK4i or DMSO (control) 12 h after stimulation with 10 nM HRG, then 100 μg/ml cycloheximide was added 16 h after stimulation with 10 nM HRG. Cells were harvested at 0, 2, and 4 h after cycloheximide treatment; n = 3. K , ErbB2 and GAPDH expression determined by western blotting. L , ErbB2 expression normalized to GAPDH expression; n = 3. The data are displayed as the means ± SDs. M , coimmunoprecipitation assay in ErbB2-overexpressing MCF-7 cells (moderate). Cells were treated with CDK4i or DMSO (control) as well as 10 μM MG132, 12 h after stimulation with 10 nM HRG, and collected 8 h later. Immunoprecipitates and whole cell lysates were immunoblotted with anti-ubiquitin or anti-ErbB2, or GAPDH antibodies. N , schematic model: In CDK4i-unresponsive WT MCF-7 cells, the loss of ErbB2 protein stability impairs the regulation of c-Myc-mediated G1/S transition, leading to the delayed G1/S transition. O , WT MCF-7 and ErbB2-overexpressing cells (moderate and high levels) were individually treated with 250 nM CDK4i or DMSO (control) 12 h after stimulation with 10 nM HRG, and images were acquired every 20 min until 72 h after stimulation. The scale bar represents 100 μm. P , Images in ( J ) were analyzed to determine the proportion (%) of each cell cycle phase in the entire set of images; n = 3. In ( B ) and ( J ), ∗ p < 0.05 (Tukey’s test). In ( D ), ∗ p < 0.05 (with respect to control and CDK4i; Welch’s t test). In ( F ) and ( H ), ∗ p < 0.05 (with respect to control and CDK4i; two-tailed Student’s t test). In ( L ), the two-way ANOVA revealed significant main effects of both time ( p < 0.0001) and CDK4i treatment (∗ p = 0.02). FUCCI, fluorescent ubiquitination-based cell cycle indicator; HRG, heregulin; PLA, proximity ligation assay; DMSO, dimethyl sulfoxide; RB, retinoblastoma protein.
Article Snippet: MCF-7 (American Type Culture Collection, ATCC, HTB-22) cells overexpressing full-length human ErbB2 (HER2) were established as follows: Human ErbB2 complementary DNA (cDNA) in the pCMV6-XL5 vector was purchased from OriGene (Catalog No: TC128161).
Techniques: Expressing, Inhibition, Western Blot, Control, Stable Transfection, Pulse Chase, Co-Immunoprecipitation Assay, Ubiquitin Proteomics, Two Tailed Test, Proximity Ligation Assay