Molecular Cloning of pTAC12 an Alternative Splicing Product of the CD3γ Chain as a Component of the Pre-T Cell Antigen-Receptor Complex

Abstract

We have reported that a 12-kDa molecule (pTAC12 as a pre-T cell receptor (TCR)-associated chain) was associated as a dimer with the pre-TCR complex as well as the clonotype-independent CD3 complex on the cell surface of immature thymocytes. We now report by protein sequencing and molecular cloning that pTAC12 is an alternatively spliced product of the CD3␥ chain lacking exon 4 containing the transmembrane region. The transcript of pTAC12 is expressed in most T cell lineages and parallels the expression of CD3␥. However, the pTAC12 protein is expressed on the cell surface of immature thymocytes but not mature T cells, despite the fact that mature T cells express a low level of pTAC12 in association with the TCR complex within the cells. These results indicate that pTAC12 may play a special role for the transport/expression and assembly of the pre-TCR⅐CD3 complex as well as the clonotype-independent CD3 complex in immature thymocytes.Thymocyte differentiation generates a functional repertoire of T cells competent for carrying out the immune response. The mechanism of thymocyte selection through the T cell receptor (TCR) 1 has been extensively analyzed, whereas the regulation of the development prior to the expression of the TCR␣␤ dimer is still largely unknown. Surface expression of the TCR␤ chain regulates a crucial step of early T cell development from CD4 Ϫ CD8 Ϫ (double negative) to CD4 ϩ CD8 ϩ (double positive) stages in TCR␣␤-expressing T cells (1). It was demonstrated that these immature thymocytes express the pre-TCR complex, which is composed of the pre-TCR␣ chain (pT␣) and the TCR␤ chain in association with the CD3 complex, before the TCR␣ gene is rearranged and expressed (2, 3). Analyses of TCR␤-(4) and pT␣-deficient mice (5) have revealed a critical role of the pre-TCR complex in the regulation of early thymocyte development. The structure of pre-TCR resembles that of pre-B cell antigen receptor, which is composed of the -heavy chain, 5, and VpreB. Although pT␣ may be equivalent to 5 because of the fact that both consist of an Ig-like constant domain, a "VpreT" molecule equivalent to VpreB has not been identified yet. Because it has been shown that CD3 and ZAP-70 are phosphorylated after stimulation by cross-linking of the pre-TCR complex with anti-CD3⑀ mAb in a cell line (6) and that Lck plays an important role for thymic development (7-9), signaling through the pre-TCR complex might be similar to that in mature T cells. However, because the physical association between the pre-TCR complex and CD3 is very weak (10 -13) and thymocytes differentiate to the double positive stage in CD3-deficient mice (14 -17), CD3 may not be essential for early T cell development. Differential assembly of the components within the pre-TCR complex may suggest a unique regulation of its assembly and expression.In addition to the pre-TCR⅐CD3 complex, the clonotype-independent CD3 (CIC) complex lacking TCR␣ and -␤ chains is present on the cell surface of immature thymocytes (18). The CIC complex, which might also be associat...

Cloning and Expression of the Rat Nephrin Homolog

“…Kendall and Thomas have shown suppression of endothelial cell growth factor activity by a secreted splice variant of vascular endothelial cell growth factor receptor lacking the transmembrane domain. 24 In addition, similar transmembrane-negative modifications generated by alternative splicing have been reported, e.g., for the T-cell receptor, 25 angiotensin-converting enzyme, 26 and interleukin-6 receptor. 27 Furthermore, the distinct functional role of such splicing variants was recently shown for the soluble receptor of advanced glycosylation, 28 which appears to be an important physiological mechanism regulating atherogenesis in hyperglycemia.…”

Nephrin is expressed in the pancreatic beta cells

“…The soluble nephrin could thus be involved in the regulation of the biological functions of nephrin. Such a mechanism is proposed for some other transmembrane proteins like the interleukin-6 receptor [18] and CD3g chain of pre-T-cell antigen receptor [19].…”

Nephrin Localizes at the Podocyte Filtration Slit Area and Is Characteristically Spliced in the Human Kidney

“…Examples of such secreted transmembrane-negative splicing variants, with biologically important regulation of the respective receptor affecting the ligand binding, include interleukin-6 receptor 25 and T cell receptor. 26 The exact role of nephrin-␣ in proteinuric diseases is currently being studied. Our preliminary results from the rat and mouse suggest that additional splicing of nephrin homologues may also occur in these species 27 at the transmembrane domain.…”