Study On The Function Of TtATG8 Gene In Autophagy Of Tetrahymena Thermophila

Autophagy is a major cellular pathway used to degrade long-lived proteins or damaged organelles such as nucleus and mitochondria in response to the cellular stress, therefore maintaining tissue homeostasis. Although a set of ATG genes and their homologues were discovered in yeast and mammalian cells, its counterparts in Tetrahymena have not been identified. Here, we isolated Tetrahymena thermophila homolog of ATG8(TtATG8), which shows high sequence similarity with ATG8of Saccharomyces cerevisiae and LC3of Homo sapines. Rapamycin treatment leads to the increase of TtATG8mRNA and EGFP-TtATG8autophagic puncta in Tetrahymena cells. Starvation induces the accumulation of TtATG8mRNA expression, autophagy and cell death in Tetrahymena. Furthermore, rapamycin pretreatment prior to starvation amplifies the induction of TtATG8mRNA expression and sustains cell viability by enhancing autophagy and preventing ATP depletion leading to cell death, which is caused by prolonged starvation. Importantly, overexpression of TtATG8extends the lifespan of Tetrahymena cells accompanied by the enhanced capability of ATP generation. Taken together, our results provide first line of evidence that TtATG8might be involved in the regulation of autophagy in Tetrahymena cells and that its induction might contribute to the longevity of Tetrahymena.