The role of KAP-1 in hypoxia


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Monica Olcina1, Ester Hammond1
1University of Oxford, Oxford, United Kingdom

Background

Severe hypoxic conditions (<0.1% O2) lead to the initiation of the DNA damage response (DDR) in the absence of detectable damage, with the induction of ATR and interestingly, ATM mediated signaling. Little is known about the mechanism of ATM activation in hypoxia, or its potential role. KAP-1 has been shown to be phoshorylated by PI3K like protein kinase family members in response to DNA damaging agents, and may play an important role in allowing chromatin relaxation to facilitate repair. We have investigated the mechanism of KAP-1 phosphorylation in response to hypoxia and its relationship to ATM activation in an attempt to clarify the potential roles of ATM in chromatin remodeling and the DDR in hypoxia.

Method

RKO, HeLa, GM1666 (ATM -/-) and GM16667 (ATM +/+) cells were used. Immunoblotting and immufluorescence were used to investigate the phosphorylation of KAP-1 in hypoxia.  Micrococcal nuclease digests were used to degrees of chromatin condensation.

Results

We have observed a rapid and persistent phosphorylation of KAP-1 in response to hypoxia occurring in an ATR-independent but ATM-dependent manner. Phosphorylation was dependent on severe oxygen concentrations and persisted during reoxygenation. Hypoxia-induced phosphorylation of KAP1  occured only in those cells in S phase. Our results point to the potential role of KAP-1 in allowing efficient repair in those cells with an active DDR. In response to severe hypoxic conditions pKAP-1 could have a potential chromatin remodeling function similar to that observed in response to DSB generating agents.

Conclusion

Targeting the DDR in hypoxia is proving to be a successful and selective therapeutic strategy. We suggest that further investigations into the relationship between ATM activation, chromatin remodeling and the DDR will provide valuable information that may aid in the understanding of the complexity of such mechanisms in physiologically relevant conditions such as hypoxia.