Fig. 7: PA28γ-T23 phosphorylation alters the cell cycle through E4F1 and enhances cell proliferation and growth in HNSCC.

a HSC-3 cells stably expressing shRNA against endogenous PA28γ were silenced with siNC or #1, #2 E4F1 siRNA. Cell numbers of cells were counted for 4 days in cell proliferation assays. b–d HSC-3 cells transduced with lentiviral EV, shPA28γ and/or shE4F1 vectors were injected into BALB/c nude mice (n = 6/group). The tumors derived from xenograft assays were dissected and photographed (b). Tumor sizes were monitored every 3 days starting one week after injection (c), and tumor masses were weighed at the endpoint (d). e, f Cell numbers of EV, PA28γ WT, PA28γ-T23A, and PA28γ-T23D-rescued HNSCC cells were counted for 4 days in cell proliferation assays (e), and the cells were seeded into 6-cm dishes in colony-formation assays (f). g–i EV, PA28γ WT, PA28γ-T23A, and PA28γ-T23D-rescued HSC-3 cells were injected into BALB/c nude mice (n = 6/group). The tumors derived from xenograft assays were dissected and photographed (g). Tumor sizes were monitored every 3 days starting one week after injection (h), and tumor masses were weighed at the endpoint (i). j–l PA28γ WT and PA28γ-T23A-rescued HSC-3 cells were silenced with siNC or #1, #2 E4F1 siRNA, and then collected for cell proliferation (j) and colony-formation (k) assays. Cells were also treated with propidium iodide staining, followed by flow cytometry analysis of DNA content (l). m, n PA28γ WT and PA28γ-T23D-rescued HNSCC cells silenced with siNC or siCK2 were collected for IB analysis (m) and colony-formation assays (n). Data in a, e, f, j–l and n represent the mean ± SD of three biological replicates; statistical significance was assessed by two-sided unpaired t-test. Source data are provided as a Source Data file.