Serum Factors Induced the Nuclear Location of Annexin V in the Human Osteosarcoma Cell Line(MG-63)

Calcium-binding proteins play essential roles in the cell. One important class of calcium-binding proteins is the annexin family. This is a family of 13 proteins, which binds to phospholipids in a calcium-dependent manner. Osteosarcoma cell line (MG-63) is a transformed cell that has many characteristics of the differentiated cell, such as a considerable serum dependency in its growth rate. Using specific antibodies against each annexin and immunoflurescence microscopy, the location and relocation of the annexin V was determined by some serum factors. Serum starvation of MG-63 cells increases their doubling time from 24 hours to 4 days. Cells grown in serum contain high levels of annexin V in the cell nucleus whereas in the absence of serum results in loss of nuclear annexin V in about 75% of the cells. Refeeding cells with medium containing 10% serum restore annexin V to the nuclei within 5 hours. Charcoal-treated serum cannot allow annexin V to return to the nucleus. Inhibition of protein synthesis with cycloheximide does not prevent the serum-induced return of annexin V to the nuclei. However, treatment of cells with genistein at a concentration specific for inhibition of tyrosine kinases (200 μM) inhibits the relocation of annexin V from cytoplasm to the nucleus. Thus, the cellular location of the annexin V depends on the growth state of the cells. It can be altered by the movement of this protein between the cytosol and the nucleus.