LC3B and ph-S6K are both expressed in epithelioid and classic renal angiomyolipoma: a rationale tissue-based evidence for combining use of autophagic and mTOR targeted drugs

Background: Targeted drugs to the autophagy processes are emerging in clinical trials. The aim of this work is to assess the magnitude of autophagic expression in renal angiomyolipoma. Methods: Fourteen cases of renal angiomyolipoma were recruited. Anti-LC3B-II and anti-phospho-S6K were detected by Western blot analysis. For immunohistochemical staining, sections were stained with the antibodies LC3B-II and cathepsin-K. LC3B-II was also analyzed by immunofluorescence. We have also carried out electron microscopy analysis on tumor cells. Results: 13 classic and 1 epithelioid renal angiomyolipoma were recruited. The Western-blot LC3B-II analysis shows increasing in protein expression in all cases, however quantitative protein expression ranged from 1 to 15 (mean 5). The autophagosome protein LC3B-I also significantly increased in all tumor extraction. The expression of LC3B-II protein was confirmed in tumoral samples by immunofluorescence. The lysosomal marker cathepsin-K was observed by immunohistochemistry on all tumours. The Western-blot ph-S6K analysis showed significant protein overexpression along all cases after evaluation of the quantitative S6K/Ponceaus ratio. In 6/14 (52%) the expression was high, with a quantitative increase of ≥3 fold induction in 4 angiomyolipoma compared to normal tissue. At electron microscopy, cancer cells evidenced round or oval electron-dense granules associated with membranes and granules with double membrane. Conclusion: Both autophagic LC3B-II and ph-S6K molecules are over-represented in both epithelioid and classic renal angiomyolipoma and a combined use of inhibitors to the autophagic and mTOR processes may be designed in clinical trials, when enrolling patients affected by tumours in tuberous sclerosis or angiomyolipoma at risk of bledding.