Bovine GM-CSF: Molecular cloning and biological activity of the recombinant protein

The lymphokine granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates the growth and differentiation of granulocytes and macrophages from bone marrow progenitors, and regulates biological functions expressed by mature cells of these lineages. In order to isolate a bovine GM-CSF cDNA, a cDNA library, generated from the BT2 bovine T cell line, was screened with a human GM-CSF cDNA probe. A cDNA clone was isolated with an insert of 783 bp, that would encode a protein of 143 amino acids, with a predicted mol. wt of 16,160. Bovine GM-CSF exhibits a high degree of sequence homology with mouse and human GM-CSF at both the nucleotide and amino acid levels. Comparison of GM-CSF amino acid sequences from the three species indicates that the bovine GM-CSF precursor contains a putative 17 amino acid signal sequence, cleavage of which would yield a 14,250 mol. wt protein. The cDNA was inserted into a mammalian expression vector and transfected into COS-7 monkey kidney cells. Biologically active bovine GM-CSF was secreted as judged by a bovine bone marrow proliferation assay. Bovine GM-CSF was weakly active in both human and mouse bone marrow proliferation assays. In contrast, human GM-CSF was weakly active on bovine but not murine mouse bone marrow cells and mouse GM-CSF was only active on murine bone marrow cells.