ATM activation and signaling under hypoxic conditions

Area of Science:

• Cellular biology
• Molecular oncology
• Biochemistry

Background:

• ATM kinase typically responds to DNA damage, mediating cell cycle arrest.
• Reoxygenation after hypoxia can induce DNA damage, activating ATM and Chk2-dependent G2 arrest.

Purpose of the Study:

• To investigate ATM kinase activation during hypoxia in the absence of DNA damage.
• To elucidate the mechanisms and signaling pathways involved in hypoxia-induced ATM activation.

Main Methods:

• Assessing ATM phosphorylation and activity via comet assays and 53BP1 focus formation.
• Evaluating ATM and ATR kinase activity under varying oxygen levels.
• Investigating the roles of hypoxia-inducible factor 1 (HIF-1), MRN complex, and MDC1 in ATM activation.

Main Results:

• ATM is phosphorylated and active during hypoxia, independent of DNA damage.
• Hypoxia-induced ATM activation correlates with replication arrest and is HIF-1 independent.
• Hypoxia-activated ATM is diffuse in the nucleus, unlike damage-activated ATM foci.
• ATM and ATR activation by hypoxia are independent of the MRN complex.
• MDC1 is required for ATM-mediated Kap1 activation under hypoxia, but does not recruit BRCA1/53BP1 or RNF8.

Conclusions:

• ATM can be activated by hypoxia through stress-specific mechanisms independent of DNA breaks.
• The MRN complex is not involved in the hypoxia-induced DNA damage response.
• MDC1 acts as an amplifier for ATM signaling in response to hypoxia, distinct from its role in DNA damage response.