A new lymphocyte-specific gene which encodes a putative Ca2+-binding protein is not expressed in transformed T lymphocyte lines

The LSP1 gene is a new lymphocyte-specific gene which is expressed in normal mouse B and T lymphocytes and in transformed B cells but not (or in much smaller amounts) in nine T lymphoma lines tested. No LSP1 mRNA is found in myeloid cells or in liver, kidney, or heart tissue. Inspection of the predicted LSP1 protein sequence reveals the presence of two putative Ca2+-binding domains in the LSP1 protein. Southern blotting analysis of genomic DNA from mouse liver suggests that the LSP1 gene is present as one copy per haploid genome. Similar analysis of genomic DNA extracted from three transformed B cell lines and five transformed T cell lines shows that the absence of LSP1 mRNA in T cell lines is not due to deletion or gross rearrangements of the LSP1 locus. With the use of the mouse LSP1 cDNA as a probe we can detect a cross-hybridizing RNA species in four normal human functional T cell lines but not in three transformed human T cell lines. This suggests that at least part of the DNA sequence and the expression pattern of the LSP1 gene is conserved between mouse and man. These conserved features, together with the particular expression pattern and the protein sequence homologies, suggest that the LSP1 protein is involved in a Ca2+-dependent aspect of normal T cell growth.