Growth-Promoting Alpha-Globulin and Ageing

In addition to growth factors of low molecular weight, most mammalian cells in continuous culture require certain proteins that are supplied in the form of dialyzed or undialyzed serum, Although some progress in identifying growth-promoting factors in serum has been made, the function of serum proteins in supporting the growth of cell cultures is not completely understood. In general, the growth-promoting properties of serum have been attributed to the alpha-globulins; we have reported the isolation of a protein from calf serum which induced mitotic activity in metazoan cells in vitro (1). The effect of the growth-promoting alpha-globulin (GPAG) is demonstrable both in primary cultures and in cell lines (2,3). It is well known that human diploid fibroblasts obtained from normal organs will multiply rapidly for several generations in vitro but will enter a stage of declining growth terminating in cell death (4). The basis for this limitation in proliferative capacity is unknown; it has been suggested that it reflects an intrinsic cell property connected with the ageing process (5).