Proliferative responses of HT29 and Caco2 human colorectal cancer cells to a panel of lectins

Altered lectin binding is common in malignant and premalignant epithelia, but its functional significance is unclear. This study examined the proliferative effects of four lectins on HT29 and Caco2 colon cancer cells. Proliferation was assessed in log growth and confluent culture by thymidine incorporation and cell counts. Peanut agglutinin (PNA) binding was characterized by Scatchard analysis and electrophoresis of lectin affinity-purified cell surface-radiolabeled preparations. PNA, 5 μg/mL, increased thymidine incorporation in HT29 but had no effect on Caco2. Wheat germ agglutinin and concanavalin A stimulated proliferation slightly at 0.5–1.0 μg/mL but were inhibitory at higher concentrations. Ulex europaeus 1 had no significant effect. Similar results were obtained when proliferation was assessed by cell counts and with confluent cell cultures. Scatchard analysis with both cell lines showed multisite best fit models with similar binding affinities. Three PNA-binding glycoproteins were identified in both cell lines, but two were of lower molecular weight in HT29 than in Caco2. Membrane preparations from a resected colorectal cancer contained a 30-kilodalton PNA-binding glycoprotein similar to that in HT29 cells. Lectins are plentiful in the normal diet and often escape digestion. This study suggests that altered expression of lectin receptors, particularly the upregulation of PNA receptor seen in colonic malignancy and hyperplasia, may have an important role in growth modulation.