Expression of the CD4 gene requires a Myb transcription factor.

Abstract

We have analyzed the control of developmental expression of the CD4 gene, which encodes an important recognition molecule and differentiation antigen on T cells. We have determined that the CD4 promoter alone functions at high levels in the CD4+ CD8-mature T cell but not at the early CD4+ CD8+ stage of T-cell development. In addition, the CD4 promoter functions only in T lymphocytes; thus, the stage and tissue specificity of the CD4 gene is mediated in part by its promoter. We have determined that a Myb transcription factor binds to the CD4 promoter and is critical for full promoter function. Thus, Myb plays an important role in the expression of T-cell-specific developmentally regulated genes.The CD4 glycoprotein is expressed on specific subsets of mature T cells and thymocytes and plays an important role both in T-cell antigen-specific activation and in T-cell development (37,47). T cells are capable of recognizing antigen only in the form of an oligopeptide bound to a membrane protein encoded within the major histocompatibility complex (MHC) (for a review, see reference 22). The antigenspecific and MHC allele-specific interaction is mediated primarily by the T-cell antigen receptor, whereas CD4 and CD8, another glycoprotein similar in function to CD4, recognize nonpolymorphic regions of the MHC molecule (10, 55). This latter interaction serves both to increase the affinity of the T cell for the antigen-presenting cell (APC) and to provide additional stimulatory signals via the tyrosine kinase pS6Ick (49). CD4 binds to MHC class II molecules and is expressed only on T cells bearing MHC class II-restricted T-cell antigen receptors (TCRs), primarily helper T (TH) cells (66). Thus, CD4 plays an important role in specifying T-cell antigen/MHC recognition and may also influence T-cell functional subclass.CD4 also plays a critical role in T-cell development. Immature thymocytes initially do not express TCR, CD4, or CD8. These CD4-CD8-(double-negative) cells differentiate to express high levels of all three molecules, forming TCR+ double-positive (CD4+ CD8+) cells that compose the largest thymocyte subpopulation (12,70). CD4+ CD8+ thymocytes that bind MHC class II molecules via the TCR and CD4 downregulate the expression of CD8 and maintain the expression of CD4; conversely, thymocytes that ligate MHC class I molecules via the TCR and CD8 molecules downregulate CD4 and maintain CD8 expression (2,29,31,58,59). This process of selection results in the mature TCR+ singlepositive (CD4+ CD8-and CD4-CD8+) populations that seed the peripheral lymphoid organs.

Elf-1 binds to a critical element in a second CD4 enhancer.

“…The J4 cosmid clone containing the murine CD4 gene was described previously (54). The J31 and J32 cosmid clones were generously provided by Rick Barth, Rochester, N.Y.…”

“…Nuclear run-on studies indicate that the primary control of CD4 expression is at the level of transcription (53), although some posttranscriptional effects on CD4 expression have also been described (45,57). Previous studies by our laboratory and others on CD4 gene regulation have identified and characterized CD4 promoter and enhancer elements in the mouse and human CD4 loci that are capable of stimulating transcription of reporter genes in transient transfections of cultured cells as well as in transgenic mice (2,49,51,54). To date, however, reconstitution of the developmental pattern and T-cell subclass-specific expression of CD4 has been accomplished only through the use of large cosmid constructs that contain many kilobases of genomic DNA sequences within and around the human CD4 locus (2,14,31 We also determined that an Ets family transcription factor, Elf-1, is a dominant protein in T-cell nuclear extracts that binds to this site in vitro.…”

Inactivation of a c-Myb/estrogen receptor fusion protein in transformed primary cells leads to granulocyte/macrophage differentiation and down regulation of c-kit but not c-myc or cdc2

“…Activation by Myb of T-lymphocyte speci®c genes such as CD4, T cell receptor d and lck tyrosine kinase and of genes which function in cell growth control such as cdc2 and c-myc has also been demonstrated (Hernandez-Munain and Krangel, 1995;McCracken et al, 1994;Cogswell et al, 1993;Ku et al, 1993;Siu et al, 1992;Nakagoshi et al, 1992;Evans et al, 1990). The bcl-2 gene, which serves an antiapoptotic function in various cell types, has very recently been reported as a Myb target gene (Salomoni et al, 1997;Taylor et al, 1996;Frampton et al, 1996).…”

The carbonic anhydrase I locus contains a c-Myb target promoter and modulates differentiation of murine erythroleukemia cells

“…However, it is unclear if these genes play a role in mediating v-Myb transformation of myeloid cells. Second, several candidate c-Myb-regulated genes have been identified based on the presence of Myb consensus DNA-binding sequences in the 5 0 flanking regions including genes encoding c-kit (Ratajczak et al, 1998), human CD34 , CD13/aminopeptidase N (Shapiro, 1995), human oxytocin receptor (Inoue et al, 1994), murine neutrophil elastase (Oelgeschlager et al, 1996;Nuchprayoon et al, 1997), mouse CD4 (Siu et al, 1992), c-Myc (Evans et al, 1990;Schmidt et al, 2000) and N-Ras (Ganter and Lipsick, 1997), although in some cases little evidence has been presented demonstrating the ability of c-Myb to regulate expression of the endogenous locus. Finally, microarray assays have been used to identify potential c-Myb target promoters in models based on forced expression of Myb family members or a dominant interfering Myb protein (Rushton et al, 2003;Lang et al, 2005).…”