Ternary complex factors SAP-1 and Elk-1, but not net, are functionally equivalent in thymocyte development.
The ternary complex factors (TCFs; SAP-1, Elk-1, and Net) are serum response factor cofactors that share many functional properties and are coexpressed in many tissues. SAP-1, the predominant thymus TCF, is required for thymocyte positive selection. In this study, we assessed whether the different TCFs are functionally equivalent. Elk-1 deletion, but not the hypomorphic Net(delta) mutation, exacerbated the SAP-1 positive selection phenotype, but triply deficient thymocytes were no more defective than SAP-1(-/-) Elk-1(-/-) cells. Inactivation of the other TCFs did not affect SAP-1-independent processes, including beta-selection, regulatory T cell selection, and negative selection, although reduced marginal zone B cells were observed in SAP-1(-/-) Elk-1(-/-) animals. Ectopic expression of Elk-1, but not Net, rescued positive selection of SAP-1(-/-) thymocytes; thus, SAP-1 and Elk-1 are functionally equivalent in this system, and the SAP-1 null selection phenotype reflects only its high expression in the thymus. Array analysis of TCR-stimulated double-positive cells identified SAP-1-dependent inducible genes whose transcription was further impaired in SAP-1(-/-) Elk-1(-/-) cells; thus, these genes, which include Egr-1 and Egr-2, represent candidate mediators of positive selection. Chromatin immunoprecipitation revealed subtly different promoter targeting between the different TCFs. Ectopic expression of Egr-1 restored positive selection in SAP-1 null thymocytes, establishing it (and possibly other Egr family members) as the major effector for ERK-SAP-1 signaling in thymocyte positive selection.
Costello
Patrick
P
Transcription Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, London, United Kingdom.
Nicolas
Robert
R
Willoughby
Jane
J
Wasylyk
Bohdan
B
Nordheim
Alfred
A
Treisman
Richard
R
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D005260:Female; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D050783:Proto-Oncogene Proteins c-ets / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D014161:Transduction, Genetic; D050807:ets-Domain Protein Elk-1 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D050808:ets-Domain Protein Elk-4 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
C494113:Elk1 protein, mouse; C086924:Elk3 protein, mouse; D050783:Proto-Oncogene Proteins c-ets; D050807:ets-Domain Protein Elk-1; D050808:ets-Domain Protein Elk-4