TGF-beta1 inhibits NF-kappaB activity through induction of IkappaB-alpha expression in human salivary gland cells: a possible mechanism of growth suppression by TGF-beta1.
Transforming growth factor (TGF)-beta is the prototype of a large superfamily of signaling molecules involved in the inhibition of proliferation of multiple epithelial cell types. Although accumulated evidence indicates the mechanisms of the antimitogenic effect of TGF-beta in a variety of cell types, the signal transduction mechanism underlying the regulation of NF-kappaB transcription factor by TGF-beta is largely unknown. Because NF-kappaB is not only involved in inflammatory responses but also mediates cell growth, we have investigated the effect of TGF-beta1 on the activity of NF-kappaB and the role of the inhibitory IkappaB-alpha protein in the growth of the human salivary gland cell clones NS-SV-AC, HSGc, and cl-1. NF-kappaB, which is usually maintained in an inactive state by protein-protein interaction with IkappaB, was found to be constitutively active in salivary gland cell lines. Upon treatment of cell clones with TGF-beta1, the NF-kappaB activity in NS-SV-AC and HSGc, but not in cl-1, which lacks the expression of TGF-beta type II receptor, was suppressed. In NS-SV-AC and HSGc, this inhibition was mediated by the induction of IkappaB-alpha at the mRNA and protein levels. The blocking of NF-kappaB subunit with a specific antisense oligonucleotide reduced the growth rate of all of the cell clones, including cl-1. Introduction of a mutated form of IkappaB-alpha cDNA into NS-SV-AC suppressed the growth rate of this cell clone. These results indicate that TGF-beta1 downregulates NF-kappaB activity through the induction of IkappaB-alpha expression in human salivary gland cells and that inhibition of NF-kappaB activity suppresses the growth rate of these cells.
Azuma
M
M
Second Department of Oral and Maxillofacial Surgery, Tokushima University School of Dentistry, 3 Kuramoto-cho, Tokushima, 770-8504, Japan. azumasa@dent.tokushima-u.ac.jp
Motegi
K
K
Aota
K
K
Yamashita
T
T
Yoshida
H
H
Sato
M
M
D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division; D002461:Cell Line, Transformed; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D015536:Down-Regulation; D015870:Gene Expression; D006131:Growth Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D020672:I-kappa B Proteins; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D012333:RNA, Messenger; D012469:Salivary Glands / Q000166:cytology / Q000378:metabolism*; D051996:Transcription Factor RelA; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D006131:Growth Inhibitors; D020672:I-kappa B Proteins; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D051996:Transcription Factor RelA; D016212:Transforming Growth Factor beta; D000072000:NF-KappaB Inhibitor alpha