CHARACTERIZATION OF AN INHIBITOR OF CELL-DIVISION RELEASED IN TUMOR-CELL CULTURES

  • 1 January 1980
    • journal article
    • research article
    • Vol. 41  (3) , 487-496
Abstract
Tumor cells may release soluble factors which inhibit the division of a variety of cells. These factors had marked immunosuppressive activity in vitro as shown by their ability to inhibit lymphocyte mitogenic responses to lectins, allogeneic lymphocytes and pokeweed mitogen-induced Ig production. These factors may play an important role in determining the outcome of tumor-host interactions in humans and may be the source of immunosuppressive factors in the circulation of patients with cancer. Characterization of these mitogenic inhibitory factors released into the supernatants of cultured tumor cells [human melanoma MM200 and human neoplastic liver Chang cells] was carried out by a number of sequential separation procedures involving affinity chromatography on wheat-germ lectin (WGL), gel filtration on PL-agarose and electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulfate (PAGE-SDS). The factors were identified throughout the separation procedure using inhibition of phytohemagglutinin (PHA) stimulation of normal lymphocytes as an index of inhibitory function. By these techniques the inhibitory activity was shown to be associated with glycoproteins containing N-acetyl-.beta.-D-glucosamine (NAcGlu) and having MW of approximately 140,000 and over 200,000 daltons. A further small MW peak of 70,000 daltons was observed on PAGE-SDS. pI [isoelectric point] values of the fractions were 7.4 and 4.2. The activity was destroyed by heating, low pH and repeated freeze-thawing but was resistant to proteolytic enzymes, deoxyribonuclease, ribonuclease and neuraminidase. The active fractions were not associated with proteolytic activity; the inhibition of mitogenic responses was irreversible in nature. These results form the basis of studies to detect this factor in biological fluids and further evaluate its role in the tumor-host relationship.