Mouse CD6: sequence of cDNA and expression of mRNA

Human CD6 is a receptor for accessory signals which can modify T cell receptor-mediated and receptor-independent T cell activation, inducing IL-2 production and cell proliferation. CD6 is a glycoprotein expressed on nearly all mature human T cells and thymocytes, some T cell leukemias, a subset of B cells and B cell lines, and in neurons of the cerebral cortex. Human CD6 is constitutively phosphorylated in resting cells, primarily on serine residues, and is additionally phosphorylated on both serine and tyrosine residues, depending on the nature of the stimuli which are used to activate the T cells. The predicted human CD6 sequence is 468 amino acids long, with typical features of a type I integral membrane protein. CD6 is a member of the macrophage scavenger receptor cysteine-rich (SRCR) super family, which includes CD5. These molecules constitute a super family that is well conserved across species boundaries. A protein of 100 kDa on human thymic epithelial cells and fibroblasts has been recently been reported to be a ligand for CD6, suggesting that CD6 may be involved in T cell development. Since little is known about CD6 expression and function in the mouse, we decided to clone CD6 cDNA. While this work was in progress, Whitney et al. independently reported the cloning and sequencing of a cDNA encoding mouse CD6. This report extends their results, as we have cloned the entire coding region and determined the nucleotide sequence of the 5' untranslated region and additional sequences of the 3' untranslated region. We also report detection of CD6 mRNA in thymus and spleen RNA and its upregulation by phorbol ester. A preliminary report of this work has been presented.