Abstract 458: Relationship between autophagy, activation and senescence in normal and cancer-associated human oral fibroblasts

Abstract

Abstract Cancer-associated fibroblasts (CAFs) isolated from oral squamous cell carcinoma (OSCC) display an activated phenotype in that they express α-smooth muscle actin (αSMA) and are frequently prematurely senescent. OSCC cell lines can induce senescence in normal fibroblasts in vitro by a mechanism that involves TGF-β and reactive oxygen species. Another phenotype closely associated with senescence is autophagy, but the relationship between autophagy, activation and senescence in CAFs has not been examined in detail. We first examined autophagosome accumulation in normal human oral fibroblasts (NHOFs; n=3) and in a panel of CAFs (n=8) that exhibited different degrees of senescence. Autophagosome accumulation was observed in senescent CAFs, as shown by the increased expression of the LC3B-II protein and by the number of LC3B cytoplasmic puncta, which were quantified using immunofluorescence. The number of LC3B puncta was significantly greater (p<0.01) in senescent CAFs compared to NHOFs, and senescent CAFs contained a higher fraction of autophagic fibroblasts than NHOFs, as indicated by increased number of LC3B puncta per cell. Further, the number of LC3B puncta correlated positively with the degree of senescence, as demonstrated by senescence-associated β-galactosidase (SA β-Gal) activity. To investigate whether autophagy, activation and senescence develop simultaneously when fibroblasts are stimulated to undergo senescence, we examined the temporal induction of these phenotypes in NHOFs in response to TGF-β1. NHOFs were treated with TGF-β1 (4 ng/ml) for up to 10 days to induce autophagy, αSMA expression and SA β-Gal activity. The results showed that autophagic flux preceded fibroblast activation, which in turn was followed by senescence. In summary, our results demonstrate that CAFs from OSCC concomitantly display autophagic, activated and senescent phenotypes and that the induction of autophagy occurs before fibroblast activation and sensecence. Taken together, these data suggest that autophagy, activation and sensecence in fibroblasts may be part of a unified programme leading to the development of CAFs. Citation Format: May Leng Tan, Eric K. Parkinson, Lee Fah Yap, Ian C. Paterson. Relationship between autophagy, activation and senescence in normal and cancer-associated human oral fibroblasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 458.