Hypothesis

Senescent cells act as microenvironmental negotiators through the SASP, but spliceosome mutations corrupt this negotiation by shifting NF‑κB and C/EBPβ isoform balances toward tumor‑promoting signals.

Mechanistic Reasoning

1. Spliceosome defects (e.g., SF3B1^K700E, U2AF1^S34F) increase inclusion of cryptic exons or intron retention in NFKB1 and CEBPB pre‑mRNAs, generating isoforms that lack transcriptional activation domains (p50‑like NF‑κB, LIP C/EBPβ).
2. These isoforms alter the NF‑κB:C/EBPβ ratio at the early DNA‑damage response hub (days 1‑3 post‑stress), biasing transcriptional output toward pro‑inflammatory SASP components (IL‑6, IL‑8, CCL2) while suppressing anti‑inflammatory mediators (IL‑10, TGF‑β).
3. The resulting SASP creates a paracrine milieu that (a) recruits and polarizes myeloid‑derived suppressor cells, (b) upregulates PD‑L1 on neighboring tumor cells, and (c) maintains low‑level proliferative signals that sustain tumor growth despite senescence arrest.
4. Because the senescent cell remains metabolically active, it continues to emit these corrupted signals, effectively acting as a “hostage negotiator” that trades short‑term tissue protection for long‑term tumor promotion.

Testable Predictions

• Isoform shift: In isogenic human fibroblast or epithelial lines engineered to carry SF3B1^K700E or U2AF1^S34F, long‑read RNA‑seq will show increased retention of intron 5 in NFKB1 and exon 2 skipping in CEBPB, raising the p50/p65 and LIP/LAP ratios (≥ 1.5‑fold change) compared with wild‑type controls.
• SASP profiling: Targeted proteomics of conditioned media will reveal elevated IL‑6, IL‑8, CCL2 (≥ 2‑fold) and reduced IL‑10/TGF‑β (≥ 50 % decrease) in mutant‑senescent cells after irradiation‑induced senescence.
• Functional outcome: Co‑culture of mutant senescent cells with autologous CD8⁺ T cells will suppress T‑cell proliferation and IFN‑γ production (≤ 30 % of control), an effect rescued by neutralizing IL‑6 or blocking PD‑L1.
• In vivo relevance: Xenograft tumors composed of SF3B1‑mutant senescent stromal cells will grow faster and show higher macrophage CD163⁺ infiltration than xenografts with wild‑type senescent stroma; senolytic clearance will reduce tumor growth only when the SASP shift is prevented (e.g., by spliceosome‑correcting antisense oligonucleotides).

Falsifiability

If spliceosome‑mutant senescent cells do not exhibit the predicted isoform changes, SASP cytokine shifts, or immunosuppressive functional effects, the hypothesis that spliceosome dysregulation converts senescent cells into corrupt negotiators would be refuted. Conversely, confirmation of these links would support a mechanistic bridge between splicing fidelity, senescence signaling, and tumor‑promoting microenvironment.