A Transcription Function for the T Cell–Specific Adapter (Tsad) Protein in T Cells

Abstract

T cell–specific adapter (TSAd) protein is an Src homology 2 (SH2) domain–containing adapter molecule implicated in T cell receptor for antigen (TCR)-mediated interleukin 2 (IL-2) secretion in T cells. Here, we demonstrate that a substantial fraction of TSAd is found in the T cell nucleus. Nuclear import of TSAd is an active process that depends on TSAd SH2 domain recognition of a phosphotyrosine-containing ligand. Importantly, we show that TSAd can act as a potent transcriptional activator in T cells. Furthermore, the TSAd SH2 domain appears to be essential for this transcription-activating function independent of its role in nuclear import. Biochemical analyses suggest that a single TSAd SH2 domain ligand of 95–100 kD may be involved in these processes. Consistent with a role as a transcription activator, cotransfection of TSAd with an IL-2 promoter–reporter gene construct results in a considerable upregulation of IL-2 promoter activity. Further, we show that this augmentation requires a functional TSAd SH2 domain. However, TSAd does not appear to modulate the activity of the major recognized IL-2 gene transcription factors, nuclear factor κB (NF-κB), nuclear factor of activated T cells (NFAT), or activator protein 1 (AP-1). These findings point to the function of TSAd as a novel transcription-regulatory protein in T cells and illustrate the importance of the TSAd SH2 domain in this role.

The C terminus of T cell‐specific adapter protein (TSAd) is necessary for TSAd‐mediated inhibition of Lck activity

“…Recently the adapter protein ALX or HSH2 was found to have substantial homology to TSAd [30]. Both ALX and TSAd were found to inhibit the activity of IL-2 promoter constructs [9,30]; however, TSAd has also been found to promote IL-2 promoter activity [10], and activated T cells from TSAd knockout mice express less IL-2 [6]. These apparently conflicting results [11] may be explained in several ways.…”

“…We previously showed that TSAd inhibits proximal signaling events in Jurkat T cells stably expressing TSAd, possibly by interfering with Lck activity [9]. Others have shown that TSAd is translocated to the nucleus in activated Jurkat T cells, and proposed that TSAd could function as a transcription adapter protein positively influencing IL-2 promoter activity [10]. T cells from mice lacking TSAd expression show reduced production of IL-2 and IFN-c [6], and these mice develop a spontaneous systemic autoimmune disease as they grow older [11].…”

Genetic association between juvenile rheumatoid arthritis and polymorphism in the SH2D2A gene

“…2 There are also indications that TSAd may be involved in transcriptional regulation in the cell nucleus. 3 Recently, it was reported that mice lacking the SH2D2A gene develop spontaneous systemic lupus-like autoimmune disease when they get older, probably due to a defect in activation-induced T-cell death. 4 The SH2D2A gene encoding TSAd contains a variable number (n ¼ 13-33) of GA repeats in its promoter region located at position À340 upstream of the first coding ATG.…”

The Related Adaptors, Adaptor in Lymphocytes of Unknown Function X and Rlk/Itk-Binding Protein, Have Nonredundant Functions in Lymphocytes

“…The two proteins exhibit 36% overall homology, and 57% when only the SH2 domains are compared (6). SH2 domain mutations in either RIBP or ALX abrogate function (8,9). Analysis of RIBPdeficient mice demonstrated that RIBP is a positive regulator of peripheral T cell activation.…”