Integration of growth factor, extracellular matrix, and retinoid signals during bronchial epithelial cell differentiation.
Epithelial cell differentiation is regulated by specific combinations of growth factors, hormones, and extracellular matrix (ECM). How these divergent signals are integrated is largely unknown. We used primary cultures of normal human bronchial epithelial cells (NHBEs) to investigate mechanisms of signal integration. In defined, serum-free media, NHBEs undergo mucosecretory differentiation only when grown in the presence of retinoids and on the appropriate substratum (collagen gels). We identified the retinoic acid receptor beta (RARbeta) gene as an early marker of NHBE differentiation. In contrast to immortalized cell lines, in NHBEs strong retinoid-induced RARbeta transcription occurs only when cells are grown on collagen gels, and it requires new protein synthesis and a cis-acting element that maps outside the known RARbeta promoter elements. NHBEs grown on collagen gels exhibit reduced epidermal growth factor (EGF)-induced Raf, MEK, and mitogen-activated protein kinase (MAPK) activity. This correlates with a specific inability to achieve high levels of p66(SHC) tyrosyl phosphorylation and association of p66(SHC) with GRB2, despite high levels of EGF receptor (EGFR) autophosphorylation. Notably, inhibition of EGFR or MEK/MAPK activation replaces the ECM requirement for RARbeta induction. Our results strongly suggest that a key mechanism by which specific ECMs facilitate retinoid-induced mucosecretory differentiation of NHBEs is by restricting the level of EGFR-dependent MEK/MAPK activation evoked by autocrine and/or paracrine EGFR ligands.
Cancer Biology Program and Division of Hematology-Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA.
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Moghal
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Neel
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D001980:Bronchi / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D003094:Collagen / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005109:Extracellular Matrix / Q000502:physiology*; D051380:GRB2 Adaptor Protein; D006133:Growth Substances / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D009077:Mucins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction / Q000502:physiology; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014212:Tretinoin / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D006133:Growth Substances; D009077:Mucins; D011506:Proteins; D018168:Receptors, Retinoic Acid; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014212:Tretinoin; D004815:Epidermal Growth Factor; D003094:Collagen; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases