A NOVEL CYTOKINE EXHIBITING MEGAKARYOCYTE POTENTIATING ACTIVITY FROM A HUMAN PANCREATIC TUMOR-CELL LINE HPC-Y5

Sixty-four kinds of cell lines were examined for their ability to prod uce megakaryocyte potentiating activity by means of conditioned media obtained from a protein-free culture system. Six human tumor cell line s were shown to produce this activity, and the cell line HPC-Y5, estab lished from human pancreatic cancer, was shown to have the highest lev el of activity. The megakaryocyte potentiating factor (MPF) was purifi ed from an HPC-Y5 conditioned medium by a combination of ion-exchange chromatography, gel filtration and reverse-phase HPLC. The purified MP F showed a megakaryocyte potentiating activity almost equal to human i nterleukin-6 in the presence of murine interleukin-3 in a colony forma tion assay with mouse bone marrow cells. The apparent molecular weight of MPF is 32,000 when determined by SDS-polyacrylamide gel electropho resis. Glycopeptidase F digestion, and amino sugar analysis of the fac tor demonstrated that MPF is a glycoprotein carrying at least one N-li nked sugar chain. The N-terminal amino acid sequence of MPF was determ ined to be y-Gln-Glu-Ala-Ala-Pro-Leu-Asp-Gly-Val-Leu-Ala-Asn. The same or homologous amino acid sequence has not been found in known protein s, demonstrating that MPF is a novel cytokine that has megakaryocyte p otentiating activity in the murine assay system.