Fig 2: Proposed model: In TNBC cells, SARS-CoV-2 M protein activated the NFκB and STAT3 signaling pathways, which are involved in mobility, proliferation and stemness, thereby facilitating in vivo metastasis. In addition, SARS-CoV-2 M protein-treated TNBC cells caused malignant transformation of non-aggressive BCC.

Fig 3: Activation of STAT3 pathway contributed to the upregulation of EMT genes and the induction of migration of BCC by SARS-CoV-2 M protein. (A) The phosphorylation of STAT3 in BCC treated with M protein. (B) Gene expression of inflammatory cytokines in MDA-MB-231 cells treated with M protein in the presence of STAT3 inhibitor. (C) EMT-related gene expression in BCC treated with M protein in the presence of STAT3 inhibitor. (D) The mRNA expression of EMT markers in MDA-MB-231 cells treated with M protein in the presence of STAT3 inhibitor. (E) Migration of BCC treated with M protein in the presence of STAT3 inhibitor. (F) The phosphorylation of STAT3 in MDA-MB-231 in the presence of M protein and the NFκB inhibitor. Galiellalactone 100 ng/ml (SC-202165; Santa Cruz Biotechnology) was used as a STAT3 inhibitor. BAY11-7082 10 μM was used as an NFκB inhibitor. U, untreated BCC; M, M protein-induced BCC. The scale bars indicate 500 µm. Each value represents the mean ± SD of triplicate experiments. (ns, no significance; p > 0.05; *p ≤ 0.05; **p ≤ 0.01).

Fig 4: HNG rapidly increase the phosphorylation of MAPK p44/42 (ERK1/2) in HEK293 cellsQuantification and representative western blots of (A) ERK activation, (B) AKT activation, and (C) STAT3 activation. Total cell lysates from HEK293 cells following 100μM HNG treatment for the indicated time periods were immunoblotted using anti-phospho- and total-ERK 1/2 (Thr202/Tyr204), AKT (Ser473), and STAT3 (Tyr705). A densitometric analysis of ERK, AKT, and STAT3 levels were performed using Image J. Data are reported as mean ± SEM of four independent experiments. *p < 0.05. Abbreviations: CM, Complete medium; SF, Serum-free medium.

Fig 5: Inhibitors block the HNG-mediated activation of ERK, AKT, and STAT3. (A) Representative western blots showing ERK, AKT, and STAT3 activation in conjunction with specific inhibitors under serum free conditions (n = 3). Quantification of (C) AKT and (D) ERK activation. Data are reported as mean ± SEM of 4 independent experiments. ***p < 0.001, *p < 0.05. Abbreviations: PD, PD98059; LY, LY294002; JAKI, JAK inhibitor I; GP, Anti-GP130 antibody.