Coordinate secretion of mouse alphafetoprotein, mouse albumin and rat albumin by mouse hepatoma-rat hepatoma hybrid cells.

Mouse heptoma cells that secrete large amounts of alpha-fetoprotein (AFP) and albumin have been crossed with rat hepatoma cells that secret only albumin, and in relatively small amounts, to investigate the influence of each parental genome upon the expression of serum proteins. All of the ten independent hybrid clones examined produce mouse AFP and both mouse and rat albumin; none produces rat AFP. The absence of production of rat AFP by the hybrids suggests that different mechanisms are involved in the initiation and in the maintenance of expression of this function. The secretion of the three proteins by the hybrid cells is coordinate: Whatever the growth phase (exponential or stationary) and irrespective of the amounts produced over a wide range, the ratio secreted of mouse AFP to mouse albumin is near to one, and that of mouse albumin to rat albumin is near to five. In addition, even though the pattern of protein secretion during the growth cycle of hybrid cells is different from those of both parents, the products of both parental genomes conform to the new hybrid pattern. Finally, some hybrids secrete less of the proteins with increasing numbers of cell generations, yet all three continue to be secreted in coordinate fashion. Since the rates of secretion of serum proteins probably reflect their rates of synthesis, we conclude that coordinate secretion indicates coordinate synthesis, and may reflect coordinate transcription of the relevant genes.