Autophagy is a cellular mechanism involved in maintaining cellular homeostasis and warranting cellular survival under stress, and may be therapeutically exploited. Autophagy assessment in vitro is well established, but analysis in formalin-fixed and paraffin-embedded (FFPE) tissue is still poorly standardized. Expression analysis of autophagy-associated markers in diagnostic FFPE tissue aids in translating in vitro findings to the clinic and may contribute to a future quest for predictive markers.
We have established a reliable visualization of autophagy-related proteins in FFPE tissue by immunohistochemistry, using lung cancer cell lines with functionally modified autophagy states and marker-depletion, respectively, and evaluated the prognostic impact of autophagy-related markers in lung cancer patients.
Dot-like staining was observed for LC3 and p62, representing the degrading autophagic vesicles. Stainings correlated significantly with quantitative protein expression assessed by western blot in cell lines and FFPE tumor tissue. In stage I/II non-small cell lung cancer cases and a large cohort of pulmonary squamous cell carcinomas, dot-like LC3 and p62 staining lacked clear prognostic value, but p62 expression was an independent prognostic factor for shorter survival in both cohorts and using internal validation models.
Valid visualization of autophagy-related markers in FFPE tissue is feasible. We could not demonstrate a clear prognostic role of autophagy status as deducted from LC3-p62 co-expression. The autophagy independent role of p62 in lung cancer warrants further investigation, as well as crosstalk with other stress factors or the role of autophagy induction during or after treatment.