Endoderm-secreted factor stimulates growth of embryonal carcinoma stem cells.

Stem cells of the embryonal carcinoma cell line called H6 can be induced to differentiate to endoderm-like cells by retinoic acid (3 X 10(-6) M). We have detected a diffusible and stable factor which is secreted by H6 endoderm-like cells and stimulates the growth of H6 stem cells. The stimulation by the endoderm-like cells is considerably greater than that by mouse fibroblasts or H6 stem cells themselves. No reciprocal stimulation of endoderm-like cells by stem cells occurs. Part but not all of the stimulation might be due to extracellular matrix proteins or to insulin-like growth factor type 2, each of which also stimulates the growth of H6 stem cells. Insulin causes no such stimulation.