Mesenchymal Expression of Nuclear Factor-κB Inhibits Epithelial Growth and Branching in the Embryonic Chick Lung

Abstract

It is becoming increasingly recognized that the ubiquitous, inducible transcription factor nuclear factor-kappaB (NF-kappaB) is involved in developmental processes. For example, NF-kappaB acts as a mediator of epithelial-mesenchymal interactions in the developing chick limb. We investigated the role of NF-kappaB in directing the branching morphogenesis of the developing chick lung, a process which relies on epithelial-mesenchymal communication. High level expression of relA was found in the mesenchyme surrounding the nonbranching structures of the lung but was not detected either in the mesenchyme surrounding the branching structures of the distal lung or in the developing lung epithelium. Specific inhibition of mesenchymal NF-kappaB in lung cultures resulted in increased epithelial budding. Conversely, expression of a trans-dominant activator of NF-kappaB in the lung mesenchyme repressed budding. Ectopic expression of RelA was sufficient to inhibit the ability of the distal mesenchyme to induce epithelial bud formation. Cellular proliferation in the mesenchyme was inhibited by hyperactivation of NF-kappaB in the mesenchyme of lung cultures. Interestingly, increased NF-kappaB activity in the mesenchyme also decreased the proliferation of the associated epithelium, while inhibition of NF-kappaB activity increased cellular proliferation in lung cultures. Expression patterns of several genes which are known to influence lung branching morphogenesis were altered in response to changes in mesenchymal NF-kappaB activity, including fgf10, bmp-4, and tgf-beta1. Thus NF-kappaB represents the first transcription factor reported to function within the lung mesenchyme to limit growth and branching of the adjacent epithelium.

Nuclear Factor-κB (NF-κB) Regulates Proliferation and Branching in Mouse Mammary Epithelium

“…Disrupting NF-B activity in embryonic limb mesenchyme impaired limb outgrowth and resulted in aberrant morphology of the apical ectodermal ridge (Bushdid et al, 1998). Similar experiments in embryonic lung demonstrated that activity of NF-B in lung mesenchyme is necessary for proper budding and growth of the adjacent lung epithelium (Muraoka et al, 2000). Based on data derived from these model systems, it is possible that NF-B activity in the mammary epithelium is regulated by paracrine signals emanating from the adjacent stroma, or even neighboring epithelial cells, to control epithelial branching and proliferation during early mammary gland morphogenesis.…”

“…For example, the increase in branching of the IB␣-deficient epithelium may be a direct result of increased proliferation, and the reduced levels of ECM expression may be due to heightened proliferation in the IB␣-deficient epithelium. Correlations between levels of proliferation and branching morphogenesis have been observed in other branching organ systems, including lung, another organ that uses NF-B to establish epithelial branching patterns through epithelial-mesenchymal interactions (Serra et al, 1994;Muraoka et al, 2000). Alternatively, the reduction of ECM may be a direct effect of increased NF-B activity.…”

“…Upon cessation of nursing, the majority of the epithelium undergoes apoptosis in a process called involution (reviewed by Furth, 1999). After involution, the epithelium remains relatively quiescent until the next pregnancy, when the morphogenetic cycle is repeated.The nuclear factor-B (NF-B) family of transcription factors regulates growth, differentiation, and apoptosis in several tissues, including lymphocytes, embryonic limb, lung and liver, skin, and bone (Beg et al, 1995;Klement et al, 1996;Boothby et al, 1997;Franzoso et al, 1997;Bushdid et al, 1998;Kanegae et al, 1998;Seitz et al, 1998;Bendall et al, 1999;Hu et al, 1999; Li et al, 1999a,b,c;Takeda et al, 1999;Tanaka et al, 1999;Chen et al, 2000a;Muraoka et al, 2000;Rudolph et al, 2000). In unstimulated cells, NF-B dimeric complexes are sequestered in the cytoplasm by association ‡ These authors contributed equally to this work.…”

NF-κB and Activator Protein 1 Response Elements and the Role of Histone Modifications in IL-1β-Induced TGF-β1 Gene Transcription

“…In the embryonic chick lung, hyperactivation of NF-B by the expression of IKK50, a constitutively active isoform of human IKK2, resulted in intense mesenchymal TGF-␤1 expression (28). Treatment with RelA antisense oligonucleotides inhibited TGF-␤1 mRNA expression in fibrosarcoma cells (19) and in monocytes from patients with idiopathic myelofibrosis (18).…”

Mechanosensitive mechanisms in transcriptional regulation

“…Physical stretching of lung epithelial cells activates NF-kB (Harding and Hooper, 1996), which enhances maturation of lung epithelial cells during embryogenesis in mouse (Londhe et al, 2008). In chicken lung, NF-kB activity in the mesenchyme also has a role during morphogenesis of lung branching (Muraoka et al, 2000). Similarly, the level of tensile prestress (isometric tension) generated by Rho-dependent changes in cytoskeletal contractility affects lung branching morphogenesis in mice (Moore et al, 2002;Moore et al, 2005).…”