Properties of colony promoting activity in procine kidney extract

Aqueous extracts prepared from procine kidneys (PKE) possess colony-promoting activity (CPA) which increases the number of granulocyte and macrophage colonies in semi-solid cultures of mouse bone marrow cells (BMC) in the presence of colony-stimulating factor (GM-CSF). PKE was totally inactivated by 15 mM N-ethylmaleimide, but was resistant to 5 mM dithiothreitol (DTT), 50 mM sodium metaperiodate and a mixture of diisopropylether-n-BuOH (3:2). The proportion of deoxyribonucleic acid (DNA)-synthesizing cells of the PKE-responsive cells was about one-half in comparison to those of CSF-responsive cells, as estimated using the hydroxyurea (HU) suicide method. Upon marrow preincubation with PKE in liquid culture for 24 h, the suicide rate of the colony forming unit in culture (CFU-C) by HU increased to 3 times compared to that of the control. Since cyclophosphamide (CY) induces a change in the number of CFU-C, the effects of PKE on BMC obtained from CY injected mice were investigated. On day 1, the number of PKE-responsive cells significantly increased by about 2.3 times in comparison with that of control, whereas the number of CFU-C per 1 x 10(4) cells significantly decreased to about one-eighth of that of control. These results suggest that a sulfhydryl group(s) is required for the appearance of the colony-promoting activity of PKE, and glycoproteins, glycopeptides or hydrophobic components are not required; they also suggest that PKE may act on immature granulocyte/macrophage progenitors, which are younger than CSF-responsive CFU-C.