Rate of Synthesis and Degradation of Lysozyme Protein by Retinoic Acid in Normal Human Airway Epithelial Cells

Yoon, Joo Heon; Hong, Seong Soo; Hong, Jung Pyoe; Lee, Geon Young; Park, In Yong

Abstract

BACKGROUND AND OBJECTIVES: We considered two possible mechanisms that might be responsible for the increased accumulation of lysozyme in retinoic acid (RA)-deficient cultures, either increased lysozyme synthesis or decreased lysozyme degradation based on our previous data. This study was to determine whether the synthesis and decay rate of intracellular lysozyme in RA-sufficient cultures are different from those in RA-deficient cultures. MATERIALS AND METHOD: Passage-2 normal human airway epithelial cells were used. For synthesis rate of lysozyme, day 10 RA-deficient and RA-sufficient cultures, incubated over 6 hour period with 35S-methionine-cysteine and cell lysates, were collected. For decay rate, day 10 cultures grown in the presence or absence of RA were labeled with 35S-methionine-cysteine for 4 hours and the labeling media were then removed. Cell extracts were collected over 8 hours. Newly synthesized or labeled lysozyme was immunoprecipitated with anti-lysozyme antibody and separated by SDS-PAGE.
RESULTS
Lysozyme synthesis rate in RA-sufficient cultures was higher than in RA-deficient cultures. In the RA-deficient cultures, the levels of newly synthesized lysozyme barely changed over the 8 hour post-labeling period. In contrast, in the RA-sufficient cultures, radiolabeled lysozyme levels decreased rapidly during the 8 hour post-labeling period, with a half-life of approximately 6 hours.
CONCLUSION
Discrepancy in mRNA and protein of lysozyme in RA-deficient cultures is due to the increased stability of lysozyme protein in RA-deficient cultures.