Cell density governs the ability of human bronchial epithelial cells to recognize serum and transforming growth factor beta-1 as squamous differentiation-inducing agents.
Sparse (75 to 2000 cells/cm2) density cultures of normal human bronchial epithelial cells uniformly undergo terminal squamous differentiation when incubated in medium containing serum (fetal bovine serum [FBS]) or transforming growth factor beta-1 (TGF-beta 1). It was found that the cell density of the culture affects the probability that a cell will respond to these differentiation-inducing agents. Thus whereas irreversible inhibition of DNA synthesis occurs in sparse cell-density cultures within 24 hours after exposure, only a transient (less than 36 hours) depression in DNA synthesis was seen in high (more than 10,000 cells/cm2) density cultures. In addition, although phase microscopic image analysis revealed that virtually all of the cells displayed a squamous morphology within 1 hour after exposure to FBS or TGF-beta 1, observations made 48 to 72 hours later showed the presence of clusters of small prolate spheroid-shaped cells surrounded by many involucrin-positive squamous-appearing cells. Only the small cells were capable of DNA synthesis and cell division as determined by autoradiography and time-lapse photomicrographic images. These replicating cells immediately undergo squamous differentiation if they are subcultured and reinoculated at low cell density and incubated in medium supplemented with FBS or TGF-beta 1. Therefore the probability that a human bronchial epithelial cell will be refractive to FBS- or TGF-beta 1 induced terminal squamous differentiation is solely a function of the cell density of the culture.
Ke
Y
Y
Division of Cancer Etiology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Gerwin
B I
BI
Ruskie
S E
SE
Pfeifer
A M
AM
Harris
C C
CC
Lechner
J F
JF
D001345:Autoradiography; D001980:Bronchi / Q000737:chemistry / Q000166:cytology / Q000187:drug effects*; D002452:Cell Count; D002453:Cell Cycle; D002454:Cell Differentiation / Q000187:drug effects*; D002460:Cell Line / Q000187:drug effects; D003114:Colony-Forming Units Assay; D004247:DNA / Q000096:biosynthesis; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects; D005312:Fetal Blood; D006801:Humans; D011498:Protein Precursors / Q000032:analysis; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D011498:Protein Precursors; D016212:Transforming Growth Factor beta; C032253:involucrin; D004247:DNA