Lactoferrin inhibits G1 cyclin-dependent kinases during growth arrest of human breast carcinoma cells

Lactoferrin inhibits cell proliferation and suppresses tumor growth in vivo. However, the molecular mechanisms underlying these effects remain unknown. In this in vitro study, we demonstrate that treatment of breast carcinoma cells MDA-MB-231 with human lactoferrin induces growth arrest at the G1 to S transition of the cell cycle. This G1 arrest is associated with a dramatic decrease in the protein levels of Cdk2 and cyclin E correlated with an inhibition of the Cdk2 kinase activity. Cdk4 activity is also significantly decreased in the treated cells and is accompanied by an increased expression of the Cdk inhibitor p21(CIP1). Furthermore, we show that lactoferrin maintains the cell cycle progression regulator retinoblastoma protein pRb in a hypophosphorylated form. Additional experiments with synchronized cells by serum depletion confirm the anti-proliferative activity of human lactoferrin. These effects of lactoferrin occur through a p53-independent mechanism both in MDA-MB-231 cells and other epithelial cell lines such as HBL-100, MCF-7, and HT-29. These findings demonstrate that lactoferrin induces growth arrest by modulating the expression and the activity of key G1 regulatory proteins.

Role of heparan sulphate proteoglycans in the regulation of human lactoferrin binding and activity in the MDA-MB-231 breast cancer cell line

We previously demonstrated that lactoferrin increases breast cell sensitivity to natural killer cell cytotoxicity whereas haematopoietic cells are unaffected by lactoferrin. It has been described that lactoferrin binds to various glycosaminoglycans. Compared to haematopoietic cells, breast cancer cells and particularly the breast cell line MDA-MB-231, possess a high level of proteoglycans. Scatchard analysis of 125I-lactoferrin binding to MDA-MB-231 cells revealed the presence of two classes of binding sites: a low affinity site with a Kd of about 700 nM and 3.9 x 10(6) sites and a higher affinity class with a Kd of 45 nM and 2.9 x 10(5) sites per cell. To investigate the potential regulation of lactoferrin activity by proteoglycans expressed on the MDA-MB-231 cells, we treated these cells with glycosaminoglycan-degrading enzymes or sodium chlorate, a metabolic inhibitor of proteoglycan sulphation. We showed that chondroitinase treatment has no effect, while heparinase or chlorate treatment significantly reduces both the binding of lactoferrin to cell surface sulphated molecules such as heparan sulphate proteoglycans (HSPG) and the affinity of lactoferrin for the higher affinity binding sites. The modulation of the lactoferrin binding was correlated with a decrease in lactoferrin activities on both MDA-MB-231 cell sensitisation to lysis and proliferation. Taken together, these results suggest that the presence of adequately sulphated molecules, in particular HSPG, is important for lactoferrin interaction and activity on the breast cancer cells MDA-MB-231.

Effects of human lactoferrin on NK cell cytotoxicity against haematopoietic and epithelial tumour cells

Lactoferrin is an iron-binding glycoprotein implicated in particular in the control of immune functions and cell proliferation. We have investigated its involvement, at inflammatory concentrations, in cancer progression. We report that lactoferrin has a significant effect on natural killer (NK) cell cytotoxicity against haematopoietic and breast epithelial cell lines. Lactoferrin increases cytolysis at a low concentration (10 micrograms/ml) while at a high concentration (100 micrograms/ml) it modulates cytolysis depending on the target cell phenotype. By pre-treatment of either NK cells or target cells with lactoferrin, we have demonstrated that the lactoferrin effect is due both to a modulation of NK cell cytotoxicity and the target cell sensitivity to lysis. Lactoferrin binds to 91% of the naturally heterogeneous CD56dim/bright NK cell population and increases the NK cell cytotoxic activity at low concentrations. High concentrations of lactoferrin seem to be toxic for the CD56bright NK cells and decrease NK cell cytotoxicity. Lactoferrin also exerts an effect on target cells depending on the cell phenotype. It does not modify the susceptibility to lysis of haematopoietic cells such as Jurkat and K-562 cells, but does significantly increase that of the breast and colon epithelial cells. We have also demonstrated that lactoferrin inhibits epithelial cell proliferation by blocking the cell cycle progression.