A NOVEL MEGAKARYOCYTE POTENTIATOR PRODUCED BY MC-1 HUMAN LUNG-CANCER CELL-LINE

The hematopoietic stimulating activity of a human lung cancer cell lin e, MC-1, was investigated. The protein fraction (MC-1 protein) was pre pared from the serum-free culture supernatant of MC-1 cells using hydr oxyapatite and concanavalin A-agarose columns. In serum-containing cul tures, MC-1 protein stimulated colony formation by megakaryocyte colon y-forming units (CFU), erythroid burst-forming units and granulocyte/m acrophage (GM) CFU. The stimulating effect was strongest for megakaryo cyte CFU. The factor having megakaryocyte colony-stimulating activity was shown to be a protein whose molecular weight was determined to be 23,000 daltons by gel filtration. By various analyses, this protein wa s shown to be molecularly different from the heretofore-identified cyt okines that may affect megakaryocytopoiesis, i.e., interleukin-l (IL-1 ), IL-2, IL-3, IL-6, IL-7, IL-11, granulocyte colony-stimulating facto r (CSF), macrophage CSF, GM-CSF, leukemia inhibitory factor, stem cell factor and tumor necrosis factor. Under serum-free conditions, MC-1 p rotein augmented murine megakaryocyte colony formation in the presence of murine IL-3 and increased the acetylcholinesterase activity of pur ified murine megakaryocytes. It was also shown that MC-1 protein stimu lated human megakaryocyte colony formation. It was concluded that MC-1 cells produce a megakaryocyte potentiator which is molecularly differ ent from any heretofore-identified cytokines.