ABSTRACT
Tumor cells secrete various growth factors and other regulatory proteins, which stimulate proliferation by binding to receptors on the cells’ own surfaces. Hematopoietic cells originate from a pluripotential precursor, known as the stem cell, which is capable of self-renewing or producing progeny which can proliferate and terminally differentiate into specialized mature cells. In various compartments of normal bone marrow, growth factors control the relation between cell proliferation and differentiation into distinct hematopoietic lineages. The mature, functionally specialized hematopoietic cells originate from a precursor, referred to as the stem cell, which has a high capacity for self-renewal and maintenance of its stem cell state. The mechanism of erythropoietin action is still not well established, but the hormone appears to induce independently either proliferation or differentiation. Human renal and hepatic carcinoma cell lines continuously produce erythropoietin in vitro. Tumor necrosis factor, a product of activated macrophages, significantly reduces both erythroid burst-forming unit and erythroid colony-forming unitn colony growth.
