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Lysozyme expression during metaplastic squamous differentiation of retinoic acid-deficient human tracheobronchial epithelial cells

 Joo-Heon Yoon  ;  Ja Seok Koo  ;  Derek Norford  ;  Karen Guzman  ;  Thomas Gray  ;  Paul Nettesheim 
 American Journal of Respiratory Cell and Molecular Biology, Vol.20(4) : 573-581, 1999 
Journal Title
 American Journal of Respiratory Cell and Molecular Biology 
Issue Date
Bronchi/cytology ; Cell Differentiation ; Cell Line ; Cornified Envelope Proline-Rich Proteins ; Epithelial Cells/drug effects ; Epithelial Cells/enzymology* ; Epithelial Cells/pathology* ; Humans ; Keratinocytes/cytology ; Keratinocytes/enzymology ; Membrane Proteins/genetics ; Metaplasia ; Mucins/genetics* ; Muramidase/genetics* ; RNA, Messenger/genetics ; Reverse Transcriptase Polymerase Chain Reaction ; Time Factors ; Trachea/cytology ; Transcription, Genetic ; Tretinoin/pharmacology ; Tretinoin/physiology*
We previously reported (Gray, T. E., K. Guzman, C. W. Davis, L. H. Abdullah, and P. Nettesheim. 1996. Mucociliary differentiation of serially passaged normal human tracheobronchial epithelial cells. Am. J. Respir. Cell Mol. Biol. 14:104-112) that retinoic acid (RA)-deprived cultures of normal human tracheobronchial epithelial (NHTBE) cells became squamous, failed to produce mucin, and instead secreted or released large amounts of lysozyme (LZ). The purpose of the studies reported here was to elucidate the relationship between RA deficiency-induced squamous differentiation and increased LZ, and to determine what mechanisms were involved. We found that intracellular LZ began to accumulate in RA-deficient NHTBE cultures early during squamous differentiation. Between Days 10 and 18 of culture, cellular LZ levels were more than 10 times higher in RA-deficient than in RA-sufficient cultures. On Day 12, large numbers of cells began to exfoliate in RA-deficient cultures and extracellular LZ appeared at the apical surface, presumably released from the exfoliated cells. Metabolic labeling studies showed that the rate of LZ synthesis was not increased in RA-deficient cultures over that in RA-sufficient cultures; however, intracellular LZ half-life was much longer in RA-deficient cultures. We concluded that the increased accumulation of both intra- and extracellular LZ in RA-deficient cultures was due to increased LZ stability and was not the result of increased LZ synthesis. When RA-deficient cultures were treated on Day 7 with 10(-6) M RA, intracellular LZ levels did not substantially decrease until 3 d later, coinciding with a marked increase in mucin secretion. LZ messenger RNA levels were unchanged at 24 h, but were modestly increased (rather than decreased) at all subsequent time points. We concluded that RA does not directly regulate LZ, and that the excessive accumulation of LZ in RA-deprived NHTBE cells is a consequence of vitamin A deficiency-induced abnormal differentiation.
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1. College of Medicine (의과대학) > Dept. of Otorhinolaryngology (이비인후과학교실) > 1. Journal Papers
Yonsei Authors
Yoon, Joo Heon(윤주헌)
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