The TRAPP complex mediates secretion arrest induced by stress granule assembly (2019)
Figure 4

Figure 4.

The association of TRAPP with SGs is under control of CDK1/2

A. Cells were treated with 273 kinase inhibitors (10 µM) from the Sellekchem library and with SA, and Sec24C localization in G3BP puncta (% of total G3BP area) was analyzed by automated microscopy as described in Methods under High content screening and is reported as a percentage of the control (cells treated with SA alone). Gray dashed line, mean of control; gray box, control standard deviation (± 18.2%); red line, threshold of positive hits; red box: positive hits.

B. Enrichment Analysis of the positive hits; for each class of inhibitor, the enrichment (in percentage) of compounds falling into positive hits and the enrichment (in percentage) in the total number of compounds was calculated and expressed as a ratio.

C. Evaluation of CDK kinase activity upon SA treatment. Western blot analysis of phosphoSer-CDK substrates in control, SA (300µM, 30 min), Dinaciclib (10 µM, 180 min) and SA+Dinaciclib (150 min Dinaciclib and 30 min SA). CDKs are hyperactivated upon oxidative stress and this activation is partially prevented upon CDK inhibition. Left, Western blot, right: Ponceau was used as loading control. Image, one representative experiment out of 3 independent replicates.

D. Drug specificity from high (++++) to low (+) of the different CDKs as described by Selleckchem, and Sec24C recruitment to SGs as a percentage of control.

E. Analysis of Sec24C recruitment to SGs in control and CDK1+2-KD HeLa cells. Different levels of CDK1+2 KD were achieved by transfecting cells with different amounts of siRNA for different times (2 nM 24 h; 5 nM 24 h; 5 nM 48 h; 20 nM 48 h) to give 50, 30, 20 and 10%, respectively, of the CDK1+2 levels in the control. CDK1+2 levels measured by qRT-PCR and Sec24C recruitment to SGs were evaluated from parallel cultures. Sec24C recruitment to SGs was performed by automated microscopy as described in (A) and is expressed as a percentage of mock (CTRL, set at 100%) ± s.d. N=8.

F. Representative images of HeLa cells treated with the three best hits (Flavopiridol, SNS-032, Dinaciclib; 1µM 150 min) and then exposed to SA (300 µM, 30 min), followed by immunostaining for Sec24C and G3BP. Scale bar, 10 µm.

G. HeLa cells were treated with Flavopiridol, SNS-032, or Dinaciclib for 150 min at the indicated concentrations, subsequently treated with SA (300 µM, 30 min), and then immunostained for Sec24C and G3BP and imaged by OPERA. BS-181, a specific CDK7 inhibitor, was used as negative control. Sec24C localization to SGs is expressed as a percentage of the control (cells treated with SA alone). Dashed red line, mean of control; yellow box, standard deviation of control (± 9.8%), N=12.

H. Cells were treated as in (G) and immunostained for TRAPPC2 and eIF3. Scale bar, 10 µm. The graph shows the quantification of TRAPPC2 localization in SG puncta (mean intensity). Data are mean ± s.e.m. expressed as a percentage of TRAPPC2 signal in SGs after Flavopiridol, SNS-032 or Dinaciclib treatment compared to the control (cells treated with SA alone). N=3, three independent experiments, n=60-80 cells per experiment. ****p<0.0001, One-way ANOVA with Dunnett's multiple comparison test.