Functional disruption of the CD28 gene transcriptional initiator in senescent T cells.
We recently reported that aging is accompanied by the emergence of CD4(+)CD28(null) T cells, a functionally aberrant lymphocyte subset rarely seen in individuals younger than 40 years. Here, we directly examined whether the lack of CD28 expression is due to a defect at the level of transcriptional initiation. Molecular studies reveal that CD28 gene transcription is controlled by two sequence motifs, sites alpha and beta. In vitro transcription assays using initiator-dependent DNA templates revealed that reversed polarity or the deletion of either motif inhibited transcription, indicating that alpha/beta sequences constitute a composite initiator. Moreover, nuclear extracts from CD28(null) cells failed to activate transcription of alphabeta-initiator DNA templates. Transcription of such templates was, however, restored with the addition of extracts from CD28(+) cells. Although previously described initiator elements have been defined by a consensus sequence, the alphabeta-initiator has no homology to such sequence. These studies demonstrate that initiators have functions other than positioning elements for the basal transcription complex. Rather, initiators can have a direct role in regulating the expression of specific genes. The gain or loss of initiator activity can be an important determinant of cell phenotypes.
Vallejo
A N
AN
Departments of Medicine and Immunology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA. vallejo.abbe@mayo.edu
Weyand
C M
CM
Goronzy
J J
JJ
D020816:Amino Acid Motifs; D018106:CD28 Antigens / Q000096:biosynthesis / Q000235:genetics*; D016922:Cellular Senescence / Q000235:genetics*; D002999:Clone Cells; D005786:Gene Expression Regulation; D006801:Humans; D012045:Regulatory Sequences, Nucleic Acid; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
D018106:CD28 Antigens; D014157:Transcription Factors