HTRF Total ATM assay principle

The Total-ATM assay quantifies the expression level of ATM in a cell lysate. Unlike Western Blot, the assay is entirely plate-based and does not require gels, electrophoresis, or transfer. The Total-ATM assay uses two labeled antibodies: one coupled to a donor fluorophore, the other to an acceptor. Both antibodies are highly specific for a distinct epitope on the protein. In presence of ATM in a cell extract, the addition of these conjugates brings the donor fluorophore into close proximity with the acceptor and thereby generates a FRET signal. Its intensity is directly proportional to the concentration of the protein present in the sample, and provides a means of assessing the protein’s expression under a no-wash assay format.

Total-ATM 2-plate assay protocol

The 2 plate protocol involves culturing cells in a 96-well plate before lysis, then transferring lysates to a 384-well low volume detection plate before the addition of the Total-ATM HTRF detection reagents. This protocol enables the cells' viability and confluence to be monitored.

Total-ATM 1-plate assay protocol

Detection of total ATM with HTRF reagents can be performed in a single plate used for culturing, stimulation, and lysis. No washing steps are required. This HTS-designed protocol enables miniaturization while maintaining robust HTRF quality.

Neocarzinostatin effect on Total and phospho Ser 1981 ATM assays

Human HEK293 cells were plated in a 96-well culture-treated plate (100,000 cells/well) in complete culture medium, and incubated overnight at 37°C, 5% CO2. Cells were treated with a dose-response of neocarzinostatin for 2h at 37 °C, 5% CO2. They were then lysed with 50 µl of supplemented lysis buffer #1 (1X) for 30 min at RT under gentle shaking. After cell lysis, 16 µL of lysate were transferred into a 384-well low volume white microplate and 4 µL of the HTRF Phospho ATM (Ser 1981) or Total-ATM detection reagents were added. The HTRF signal was recorded after an overnight incubation at room temperature. As expected, neocarzinostatin induced single and double strand DNA damage, leading to a dose-dependent increase of ATM phosphorylation, without any effect on the expression level of the ATM total protein.

ATM/CHK2 and ATR/CHK1 signaling pathways

DNA double-strand breaks (DSBs) or single-strand breaks (SSBs) are among the most deleterious lesions that threaten genome integrity. They can be induced by the effect of cellular metabolites or by DNA-damaging agents such as genotoxic compounds, chemotherapeutic agents, ultraviolet (UV) irradiation, or ionizing radiation.
 

DNA damage response (DDR) is mainly controlled by ataxia telangiectasia mutated (ATM) and by ataxia telangiectasia and Rad3-related (ATR), two members of the phosphoinositide 3-kinase (PI3K)-related kinase (PIKK) protein kinase family.

Reacting to DNA damage (DSBs), the ATM–Chk2 pathway and replication checkpoint responses are activated,h mediating G1/S checkpoints to arrest cell cycle progression and allow extra time for DNA repair.

Also in response to DNA DSBs, ATM autophosphorylates to generate the active monomeric kinase. Activation of ATM results in the phosphorylation of a diverse array of downstream targets, such as the H2A histone family member X, H2Ax, or the checkpoint kinase Chk2 and its downstream effectors.

The isolation of new small molecule inhibitors of ATM, and the design and validation of novel strategies of checkpoint modulation, combined with the traditional radiation and chemotherapy modalities, hold promise for improved treatment of cancers.