Kinase activity analysis of SARS-CoV-2 phosphorylation profiles predicted upregulation of several components of the p38/mitogen-activated protein kinase (MAPK) signaling pathway, including MAP2K3, MAP2K6, MAPK12, MAPKAPK2 (MK2), and MAPKAPK3 (Figures 6A and 6B). Immunoblotting for activated phospho-p38 (T180/Y182), phospho-MK2 (T334), and phospho-cAMP response element-binding protein (CREB) and phospho-ATF-1 at their respective MAPKAPK2 sites (S133 in both) confirmed activation of the p38/MAPK pathway during SARS-CoV-2 infection in ACE2-expressing A549 human lung carcinoma cells (ACE2-A549) (Figure 6C). Furthermore, phosphoproteomics data depict increased phosphorylation of p38 pathway substrates such as negative elongation factor E (NELFE), heat shock protein beta-1 (HSPB1), and signal transducer and activator of transcription 1-alpha/beta (STAT1), among others (Figure 6D). Regulation of these sites occurs late in the time course (24 h after infection), likely reflecting a more advanced stage of viral infection, replication, and egress.
Figure 6 SARS-CoV-2 Activates the p38/MAPK Signaling Pathway and Causes Cell Cycle Arrest
(A) Diagram of the p38/MAPK signaling pathway.
(B) Kinase activity analysis for kinases in the p38/MAPK pathway.
(C) Western blot analysis of phosphorylated p38/MAPK signaling components in mock- and SARS-CoV-2-infected ACE2-A549 cells 24 h after infection.
(D) Log2 fold change profiles of indicated p38/MAPK substrates during SARS-CoV-2 infection in Vero E6 cells.
(E) Transcription factor activity analysis of SARS-CoV-2-infected A549, Calu-3, and NHBE cells, comparing p38/MAPK transcription factors with transcription factors not associated with the p38/MAPK pathway. Statistical test: Mann-Whitney test.
(F) qRT-PCR analysis of the indicated mRNA from ACE2-A549 cells pre-treated with the p38 inhibitor SB203580 at the indicated concentrations for 1 h prior to infection with SARS-CoV-2 for 24 h. Statistical test: Student’s t test. See also Figures S4 and S5.
(G) Heatmap of Pearson’s correlation coefficients comparing SARS-CoV-2-infected Vero E6 phosphorylation profiles with profiles of cells with induced DNA damage and cells arrested at the indicated cell cycle stages.
(H) Log2 fold change profiles of the indicated cell cycle and DNA damage substrates during SARS-CoV-2 infection in Vero E6 cells.
(I) DNA content analysis of cells infected with SARS-CoV-2 for 24 h compared with mock-infected cells.