Novel kinetics, behaviour and cell-type specificity of CD157-mediated tyrosine kinase signalling.

CD157, a recently characterized leukocyte surface antigen, has recently been shown to induce tyrosine phosphorylation of a 130-kDa protein (p130) when cross-linked with its antibody (ligand). We have further investigated the detailed kinetics, behaviour and cell-type specificity of this CD157-stimulated p130 phosphorylation. We demonstrate that CD157-mediated p130 phosphorylation is ligand independent in recombinant CD157-expressing CHO, MCA102 and COS-7 cells but is ligand dependent in HL-60-differentiated monocytes (mHL-60) having enhanced CD157 expression. This p130 phosphorylation is activated only at lower temperatures (0-4 degrees C) in MCA102, COS-7 and mHL-60 cells but is temperature insensitive in CHO cells. We further demonstrate that the CHO/CD157 cell clones have approximately 22-28% slower rates of proliferation than that of a CHO/mock clone. But the MCA102 cell proliferation remains unaffected by CD157 expression. We postulate that the difference in the temperature sensitivity of p130 phosphorylation can be responsible for the discrepancy in the rates of MCA102/CD157 and CHO/CD157 cell proliferation.