Ataxia telangiectasia and Seckel syndrome are devastating human neurological diseases that are caused by mutations in two similar genes: ATM (ataxia-telangiectasia mutated) and ATR (ATM and Rad3-related). ATM and ATR are known as canonical DNA damage response (DDR) kinases; but, both proteins have a significant cytoplasmic presence that has only recently been unearthed. Both proteins associate with synaptic vesicles as well as proteins involved in clathrin-mediated endocytosis. Additionally, Atm^-/- mice demonstrate a distinct reduction in hippocampal long-term potentiation, suggesting that synaptic ATM has an important functional role. To more efficiently understand how ATM and ATR affect vesicle endocytosis and trafficking, we have adopted a different experimental model – the buddi...[ Read more ]

Ataxia telangiectasia and Seckel syndrome are devastating human neurological diseases that are caused by mutations in two similar genes: ATM (ataxia-telangiectasia mutated) and ATR (ATM and Rad3-related). ATM and ATR are known as canonical DNA damage response (DDR) kinases; but, both proteins have a significant cytoplasmic presence that has only recently been unearthed. Both proteins associate with synaptic vesicles as well as proteins involved in clathrin-mediated endocytosis. Additionally, Atm^-/- mice demonstrate a distinct reduction in hippocampal long-term potentiation, suggesting that synaptic ATM has an important functional role. To more efficiently understand how ATM and ATR affect vesicle endocytosis and trafficking, we have adopted a different experimental model – the budding yeast, Saccharomyces cerevisiae. The yeast orthologues of ATM (TEL1) and ATR (MEC1) have also been extensively studied in relationship to DDR. Our first question was whether TEL1 or MEC1 affects yeast endocytosis. Using FM4-64, which is internalized into yeast via the endocytic pathway, we found that TEL1 knockout (KO) and MEC1 heterozygous yeast strains demonstrated a robust increase in endocytic efficiency. Despite this genetic evidence, TEL1 KO/MEC1 heterozygous yeast were resistant to the mammalian ATM and ATR inhibitors (KU-60019 and VE-822, respectively) with respect to their growth rates. We also examined how the TEL1/MEC1 phenotype related to other intracellular trafficking pathways, specifically the recycling pathway. Using a GFP-SNC2 fusion protein as a recycling marker, we found no observable difference in GFP-SNC2 steady state distribution in either TEL1 KO or MEC1 heterozygous strains. Thus, guided by our mammalian findings, we have discovered a novel endocytic phenotype associated with deficiencies in TEL1 and MEC1. This phenotype seems to act independently of the closely-associated recycling pathway. Already, these discoveries have guided other, current experiments in the mammal and will serve as a powerful platform to dissect the vesicle-related functions of ATM and ATR.