Reversible inhibition of proliferation of epithelial cell lines by Agaricus bisporus (edible mushroom) lectin
Yu, L.; Fernig, D.G.; Smith, J.A.; Milton, J.D.; Rhodes, J.M.
Cancer Research 53(19): 4627-4632
1993
ISSN/ISBN: 0008-5472 PMID: 8402638 Document Number: 419090
Galactosyl beta-1,3-N-acetyl galactosamine (Gal beta-1,3-GalNAc) (Thomsen Friedenreich antigen), the Class I core sequence in O-linked oligosaccharide chains, behaves as an oncofetal antigen showing increased expression in many epithelial malignancies. Previous work has shown that peanut agglutinin (PNA), a lectin that binds Gal beta-1,3-GalNAc, stimulates proliferation in HT-29 (human colon cancer) cells and normal human colonic epithelium and this implies that cell surface glycoproteins which express Gal beta-1,3-GalNAc may play an important role in the regulation of epithelial cell proliferation. We have now studied the effect on epithelial cells of another dietary Gal beta-1,3-GalNAc-binding lectin, the edible mushroom Agaricus bisporus lectin (ABL). This differs from PNA in its ability to bind also to sialylated Gal beta-1-3-GalNAc. In contrast to PNA, A-BL (25 mu-g/ml) inhibited incorporation of (3H)thymidine into DNA of HT29 colon cancer cells by 87% (95% confidence limit, 85-89%), Caco-2 colon cancer cells by 16% (95% confidence limit, 12-20%), MCF-7 breast cancer cells by 50% (95% confidence limit, 47-52%), and Rama-27 rat mammary fibroblasts by 55% (95% confidence limit, 51-60%) when these cells were grown for 24 h in serum-free medium. When assessed by cell count, similar inhibition of proliferation of HT29 cells by ABL was found. In the presence of 2% fetal calf serum (which contains the ABL-binding glycoprotein fetuin), the inhibitory effect of ABL on cell proliferation was still demonstrable but at increased ABL concentration (60 mu-g/ml for 49% inhibition). Ten mu-g/ml ABL completely abolished the stimulatory effect on (3H)thymidine incorporation of epidermal growth factor (100 pg/ml) and PNA (25 mu-g/ml) and markedly inhibited the stimulatory effect of insulin (50 ng/ml). ABL (0.2 mg/ml) caused no cytotoxicity to HT29, MCF-7, and Rama-27 cells as measured by trypan blue exclusion, and inhibition of proliferation in HT29 cells caused by 50 mu-g/ml ABL was reversible after removal of the lectin. Binding studies with 125I-labeled ABL suggested a single class of binding site with an apparent K-d value of (4.12 +- 0.29) times 10-7 M with (3.6 +- 0.3) times 10-7 binding sites/cell. A. bisporus lectin is a reversible noncytotoxic inhibitor of epithelial cell proliferation which deserves study as a potential agent for cancer therapy.