Soluble factor in normal tissues that stimulates high-molecular-weight sialoglycoprotein production by human colon carcinoma cells

The stimulation of high molecular weight sialoglycoprotein synthesis by a soluble factor derived from normal colon tissues was studied in vitro with human colon carcinoma cell lines, HT-29 P and a metastatic variant HT-29 LMM. The synthesis of all three high-molecular-weight sialoglycoproteins (approximate Mr 900,000, 740,000, and 450,000) by HT-29 P cells or HT-29 LMM cells growing in vitro was enhanced by supplementing the culture medium with a conditioned medium of fresh human colon organ culture. Changes were detected by polyacrylamide gel electrophoresis of lysates from [3H]glucosamine-labeled cells on 3% gels followed by fluorography, or by electrophoresis of lysates from unlabeled cells followed by incubation with 125I-labeled wheat germ agglutinin and autoradiography. No changes were detected in the major protein components or in glycoproteins at Mr less than 200,000 as revealed by polyacrylamide gel electrophoresis. The treated cells did not change their growth rate or morphology. The connective tissue portions of the colon tissues were apparently responsible for the production of this stimulatory substance. The stimulatory activity was preserved at 56 degrees C but was inactivated by heating at 100 degrees C. The substance was eluted from a Sephacryl S-200 column at a position between the elution positions of ovalbumin and trypsinogen. The colon carcinoma cells treated with the conditioned medium and producing increased amounts of high-molecular-weight sialoglycoproteins were less sensitive to the cytolytic effects of recombinant interleukin 2-activated human peripheral blood lymphocytes than untreated cells were. The treated colon carcinoma cells induced stronger platelet aggregation than their untreated counterparts did. Therefore, this substance may represent one of the normal host tissue factors that can influence and modulate malignant behavior of carcinoma cells growing in vivo.