Hypothesis: In naturally aged cells, increased CK2 kinase activity and reduced DUSP6 phosphatase activity shift the equilibrium of ERK1/2 toward sustained nuclear import, which activates senescence-associated protein degradation (SAPD) of HSP70 and STAT3 and promotes telomere-driven replicative senescence. Conversely, restoring DUSP6 activity or inhibiting CK2 favors cytoplasmic ERK retention, attenuates SAPD, and extends healthspan without increasing oncogenic transformation risk.

Testable predictions

1. Biochemical signature – Compared with young (3‑month) tissues, old (24‑month) mouse liver, kidney, and skin will show: (a) elevated CK2 phosphorylation of the ERK1/2 SPS motif (Ser244/Pro245/Ser246) measured by phospho‑specific antibodies; (b) decreased DUSP6 protein levels and phosphatase activity; (c) higher ERK1/2 nuclear/cytoplasmic ratio assessed by subcellular fractionation or imaging.
2. Functional link to SAPD – Inhibition of CK2 (using CX‑4945) or overexpression of DUSP6 in primary fibroblasts from old donors will reduce nuclear ERK, decrease degradation of HSP70 and STAT3 (measured by ubiquitin‑proteasome assay), and lower SA‑β‑Gal and IL‑6 expression, whereas CK2 activation or DUSP6 knockdown in young cells will phenocopy aged SAPD.
3. In vivo relevance – Treatment of aged mice with a CK2 inhibitor or AAV‑mediated DUSP6 hepatic expression will: (a) lower nuclear ERK in hepatocytes; (b) diminish markers of replicative senescence (telomere‑associated foci, p16^INK4a); (c) improve functional readouts (glucose tolerance, grip strength) without increasing tumorigenesis over a 6‑month period.
4. Specificity of the ERK‑SAPD route – The senescence‑modulating effects of CK2/DUSP6 manipulation will be abrogated by co‑treatment with the proteasome inhibitor MG‑132 or by expressing non‑degradable HSP70/STAT3 mutants, confirming that SAPD is required for the phenotype.

Potential confounders and controls

• Verify that observed changes are not secondary to global transcriptional shifts by normalizing to housekeeping proteins and using ERK‑independent senescence models (e.g., irradiation).
• Assess off‑target effects of CK2 inhibitors on AMPK/mTOR pathways, which also influence autophagy, by measuring LC3‑II and p‑S6K levels.
• Include p53‑null fibroblasts to test whether the ERK‑SAPD axis functions independently of classic DNA‑damage‑induced senescence.

Falsification If aged tissues show no increase in CK2‑mediated SPS phosphorylation or no decrease in DUSP6 activity, or if modulating CK2/DUSP6 fails to alter ERK localization, SAPD, or senescence markers, the hypothesis would be refuted. Conversely, if CK2/DUSP6 manipulation changes ERK shuttling but does not affect senescence outcomes, the proposed causal link would be invalid.

ERK nuclear import mechanism MEK inhibitors extend fibroblast lifespan MEK/ERK suppression activates autophagy Nuclear vs. cytoplasmic ERK determines fate