Role of lipopolysaccharide and IL-4 in control of transcription of the class II A alpha gene.
The class II (Ia) MHC molecules are cell surface proteins that regulate the activation of T cells. B lymphocyte expression of class II molecules has been shown to be influenced by a number of external stimuli. It has been previously demonstrated that treatment of these cells with IL-4 leads to an increase in class II gene transcription at 18 h as well as to an increase in steady state class II mRNA. It has also been previously demonstrated that LPS treatment of splenic B cells from athymic mice results in a decrease in steady state mRNA encoding the A alpha class II protein. This decrease persists for at least 18 h. Nuclear run-on transcription assays now demonstrate that although steady state mRNA levels for A alpha are decreased by LPS treatment of athymic mouse lymphocytes, LPS does not decrease A alpha gene transcription, but rather modestly activates transcription of this class II gene. LPS and IL-4 have been demonstrated to be synergistic stimuli for a number of genes. Costimulation of splenic lymphocytes from athymic mice with IL-4 plus LPS leads to activation of transcription, but the increase in transcription is no more than that seen with IL-4 stimulation alone. However, in costimulated lymphocytes, steady state A alpha-encoding mRNA levels are intermediate between the increased levels seen with IL-4 stimulation and the decreased levels seen with LPS stimulation. Therefore, LPS and IL-4 act nonsynergistically in class II gene transcription and the effects of LPS in decreasing steady state mRNA are most likely posttranscriptional. An IL-4-inducible and an LPS-inducible DNA-binding protein have been previously identified in splenic lymphocytes from athymic mice. Both nuclear binding proteins form complexes with the same DNA fragments from a control region of the A alpha gene. These nucleoprotein complexes comigrate under nondenaturing conditions and display identical patterns of binding with a panel of oligonucleotide competitors. Oligonucleotides representing protein binding sites of the IL-4 and LPS-induced DNA-binding proteins cross-compete for protein binding. Therefore, the binding proteins induced by LPS and IL-4 are likely related, and may function at different efficiencies as activators of A alpha gene transcription.
Gravallese
E M
EM
Department of Cancer Biology, Harvard School of Public Health, Boston, MA 02115.
Darling
J M
JM
Glimcher
L H
LH
Boothby
M
M
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D001483:Base Sequence; D001667:Binding, Competitive; D016827:CD8 Antigens / Q000235:genetics; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D005802:Genes, MHC Class II; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D015847:Interleukin-4 / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000502:physiology*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D011948:Receptors, Antigen, T-Cell / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*
D016827:CD8 Antigens; D004268:DNA-Binding Proteins; D000949:Histocompatibility Antigens Class II; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D015847:Interleukin-4; D003513:Cycloheximide