Downregulated adaptor protein p66(Shc) mitigates autophagy process by low nutrient and enhances apoptotic resistance in human lung adenocarcinoma A549 cells

Abstract

Macroautophagy or autophagy is a lysosome-dependent process in which enzymatic degradation and recycling of cytosolic components occur in stressful contexts. The mechanisms underlying the signaling from starvation to the regulation of autophagy are not fully understood. We previously showed that the Src family member p66(Shc) (focal adhesion-associated 66 kDa isoform of the Src homology and collagen) promotes anoikis and suppresses tumor metastasis via k-Ras-dependent control of proliferation and survival. However, the role of p66(Shc) in low-nutrient-induced autophagy-related pathways remains elusive. In this work, human lung adenocarcinoma A549 cells were used to further investigate the biological effects of p66(Shc) on autophagy and apoptotic resistance. Here, we show that deficiency of p66(Shc) mitigates the low-nutrient-induced autophagy process in the levels of microtubule-associated protein 1A light chain protein 3B (LC3B) conversion, in the number of autophagic vacuoles and in p62/sequestosome 1 protein degradation. However, autophagy-related protein Beclin 1 was not significantly changed during low-nutrient treatment. Furthermore, we found that prolonged phosphorylation of extracellular signaling-regulated kinase (Erk)1/2, but not phosphorylation of Akt is significantly sustained when p66(Shc) expression is inhibited by shRNA. In addition, cleavage of caspase 7 and poly(ADP-ribose) polymerase, but not caspase 6 and 9 are retarded with this effect compared to the shRNA control cells. Together, these findings suggest the possibility that p66(Shc) plays a pivotal role in coordinately regulating autophagy process and apoptotic resistance in A549 cells under nutrient-limited conditions.

Keywords: adaptor protein; apoptotic resistance; autophagy; nutrient deprivation; p66Shc.