Ceruloplasmin, a copper-transport protein, can act as a growth promoter for some cell lines in serum-free medium

Ceruloplasmin releases pH-induced inhibition of cell proliferation stimulated by growth factors

Swiss 3T3 fibroblasts can be weakly stimulated to grow by bombesin, epidermal growth factor or ceruloplasmin when cells are maintained in Dulbecco's Modified Essential Medium (DMEM), the pH of which is 7.75. Addition of insulin synergizes with the other mitogens. However, only ceruloplasmin promotes DNA synthesis in Minimum Essential Medium (MEM). The pH in this medium is 7.0. All the other growth factors synergize with the ceruloplasmin effects, but such synergism is not evident with insulin. If the pH in MEM is increased to 7.25 or 7.75 by supplementation with HEPES or NaHCO3, respectively, the results are similar to those found in DMEM. Since the oxidation of iron is increased at alkaline pH, the reoxidation of iron at the cell surface may facilitate growth at alkaline pH. We propose that iron reoxidation is limiting for cell growth and that part of the ceruloplasmin effect is mediated by its action as a terminal oxidase for ferrous iron on the cell surface. Observations consistent with this explanation include: 1) combinations of insulin with bombesin or epidermal growth factors do not promote cell proliferation at pH 7.0; 2) fetal calf serum, which has ferroxidase activity, and ceruloplasmin plus or minus other growth factors stimulate cell proliferation at pH 7.0; and 3) alkaline pH also restores the mitogenic effect of growth factors.

Ceruloplasmin stimulates thymidine incorporation by CCL-39 cells in the absence of serum or growth factors

The incorporation of tritiated thymidine into CCL-39 cells grown in the absence of fetal calf serum or other growth factors is greatly increased by low concentrations of ceruloplasmin. The stimulation is greater than observed with serum or thrombin. Addition of serum decreases the thymidine incorporation with ceruloplasmin to the level with serum alone. As with serum, the response to ceruloplasmin is high at both 20% and 1% oxygen, which is consistent with the action of ceruloplasmin as an oxidant with a high affinity for oxygen. Since transplasma membrane electron transport increases cell growth and thymidine incorporation, ceruloplasmin may act as a terminal oxidase for ferrous iron or ascorbate to stimulate transplasma membrane electron transport. The four electron transfer from ceruloplasmin to oxygen to form water will prevent peroxide formation at the cell surface. Alternatively, superoxide formation inside the cell or membrane could employ the superoxide dismutase function of ceruloplasmin to produce peroxide. Either mechanism would be consistent with the previously described stimulation of growth by external oxidants.

The effects of various nutritional supplements on the growth, migration and differentiation of Xenopus laevis neural crest cells in vitro

This study investigates the nutritional requirements of Xenopus laevis neural crest cells and melanophores developing in vitro. A comparison is made between the growth and differentiation of cells in serum-containing medium and a chemically defined, serum-free medium that we have designed. Our chemically defined medium is more efficient than serum-supplemented medium in promoting proliferation of these cells. Several supplements are required to enhance culture development. These include insulin, alpha-melanocyte stimulating hormone, somatotropin, luteotrophic hormone, linoleic acid, uridine, and putrescine. In addition, collagen and fibronectin provide the most conducive environment tested for cell migration and adhesion.

The expression of ceruloplasmin, an angiogenic glycoprotein, by mouse embryonic fibroblasts

Balb/c 3T3, Swiss 3T3 and Rous sarcoma virus transformed Balb/c 3T3 mouse embryonic fibroblasts produced ceruloplasmin in vitro, whereas primary cultures prepared from the Balb/c mouse embryos did not produce ceruloplasmin. The amount of ceruloplasmin synthesis by the Balb/c 3T3 cell line is enhanced by Rous sarcoma virus-transformation (1.5-3 fold) and by treatment with dexamethasone (about 2.4 fold). The protein was identified as ceruloplasmin by immunoprecipitation with ceruloplasmin-specific polyclonal antibody, and by similarity of peptide maps, and subunit molecular weight (135,000 dalton) to that of authentic ceruloplasmin from primary cultures of mouse hepatocytes.