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Maturational differences in hyperoxic AP-1 activation in rat lung
1Department of Pediatrics, Stanford University, Palo Alto, California 94305, USA.
Insights
Neonatal lungs show different activator protein (AP)-1 binding complexes than adults when exposed to hyperoxia. These maturational differences in AP-1 may explain varying gene regulation responses to oxygen.
Area of Science:
- Pulmonary Medicine
- Molecular Biology
- Developmental Biology
Background:
- Hyperoxic injury affects neonates and adults differently.
- Activator protein (AP)-1 is involved in hyperoxic gene regulation.
Purpose of the Study:
- To evaluate lung AP-1 binding and its subunit proteins in neonatal and adult responses to hyperoxia.
- To investigate maturational differences in AP-1 complexes.
Main Methods:
- Exposure of neonatal and adult organisms to hyperoxia (>95% O2) for 3 days.
- Evaluation of lung AP-1 binding and subunit proteins (c-Fos, c-Jun, phosphorylated c-Jun, Jun B, Jun D) using supershift and sequential immunoprecipitation assays.
Main Results:
- Neonatal lungs showed no increased AP-1 binding in hyperoxia, unlike adults.
- Neonatal lungs exhibited two distinct AP-1 binding complexes (Fos/Jun family and Jun family, predominantly Jun D), while adult lungs had one complex possibly involving other proteins.
- Neonatal lungs had higher levels of Jun B and Jun D proteins under both air and hyperoxia compared to adults.
Conclusions:
- Significant maturational differences exist in lung AP-1 complexes between neonates and adults.
- These differences in AP-1 complex composition may underlie distinct transcriptional responses to hyperoxic gene regulation in immature versus adult lungs.
Abstract:
Immature organisms (neonates; <12 h old) have vastly differing responses to hyperoxic injury than adults. A common feature of hyperoxic gene regulation is involvement of activator protein (AP)-1. We evaluated lung AP-1 binding as well as that of the AP-1 subunit proteins c-Fos, c-Jun, phosphorylated c-Jun, Jun B, and Jun D after exposure to >95% O(2) for 3 days. Unlike adults, neonates showed no increased AP-1 binding in hyperoxia despite a high affinity of the AP-1 binding complexes for phosphorylated c-Jun and Jun D as demonstrated by supershift of these antibodies with the AP-1 complexes. Moreover, neonatal lungs exhibited two distinguishable AP-1 binding complexes, whereas adult lungs had one. In neonates, sequential immunoprecipitation revealed that the lower AP-1 complex was composed of proteins from both the Fos and Jun families, whereas the upper complex consisted of Jun family proteins, with predominance of Jun D. In adults, the single AP-1 complex appeared to involve other Fos or non-Fos or non-Jun family proteins as well. Neonatal lungs showed a higher level of Jun B and Jun D immunoreactive proteins in both air and hyperoxia compared with those in adult lungs. These results suggest that significant maturational differences in lung AP-1 complexes exist and that these may explain transcriptional differences in hyperoxic gene regulation.