ATM serine/threonine kinase

Schematic illustration of the four known conserved domains in four members of the PIKKs family

ATM-mediated two-step response to DNA double strand breaks. In the rapid response activated ATM phosphorylates effector kinase CHK2 which phosphorylates CDC25A, targeting it for ubiquitination and degradation. Therefore, phosphorylated CDK2-Cyclin accumulates and progression through the cell cycle is blocked. In the delayed response ATM phosphorylates the inhibitor of p53, MDM2, and p53, which is also phosphorylated by Chk2. The resulting activation and stabilization of p53 leads to an increased expression of Cdk inhibitor p21, which further helps to keep Cdk activity low and to maintain long-term cell cycle arrest.

ATM serine/threonine kinase (ATM), also known as ataxia telangiectasia mutated, is a protein that in humans is encoded by the ATM gene. ATM is a key player in the cell cycle control and DNA damage response pathways, making it crucial for maintaining genetic stability and preventing cancer.

Function

ATM is a member of the PI3K/PIKK family of protein kinases, which are involved in cellular processes such as DNA repair, cell cycle progression, and apoptosis. Upon DNA damage, particularly double-strand breaks (DSBs), ATM is rapidly activated and phosphorylates several key proteins that initiate the DNA damage response (DDR). This includes the phosphorylation of p53, CHK2, and BRCA1, among others, leading to cell cycle arrest, DNA repair, or apoptosis if the damage is irreparable.

Clinical Significance

Mutations in the ATM gene are associated with Ataxia Telangiectasia (A-T), a rare, autosomal recessive disorder characterized by neurodegeneration, immunodeficiency, increased risk of cancer, and sensitivity to ionizing radiation. Individuals with A-T exhibit symptoms such as difficulty coordinating movements (ataxia) and dilated blood vessels (telangiectasia), particularly in the eyes and skin. The ATM protein's role in DNA repair and cell cycle control underlines the diverse symptoms observed in A-T, reflecting the importance of ATM in various cellular functions beyond DNA damage response.

ATM in Cancer

Given its central role in DNA repair and cell cycle regulation, ATM is considered a critical factor in the development and progression of cancer. Loss of ATM function leads to genomic instability, a hallmark of cancer, facilitating the accumulation of mutations that drive tumorigenesis. Consequently, ATM is a target for cancer therapy, with researchers exploring strategies to inhibit or modulate its activity in cancer cells, particularly in tumors with existing defects in DNA repair pathways.

Structure

The ATM protein is a large, multidomain serine/threonine kinase. It contains a FAT domain, a kinase domain, and a FATC domain at its C-terminus. The FAT and FATC domains are thought to regulate the kinase activity and are named after the proteins FRAP, ATM, and TRRAP that share this domain structure. The precise mechanism of ATM activation involves autophosphorylation and dimer dissociation in response to DNA damage, although the full details of this process are still under investigation.

Research and Future Directions

Research on ATM continues to uncover its complex role in cellular processes and its potential as a therapeutic target. Understanding the precise mechanisms of ATM activation and function in DNA repair and cell cycle control is crucial for developing targeted therapies for cancer and possibly other diseases associated with DNA damage and repair defects. Additionally, the study of ATM's role in neurodegeneration offers hope for interventions in diseases like Ataxia Telangiectasia and possibly other neurological disorders.