Phorbol ester-stimulated murine myelopoiesis: role of colony-stimulating factors

Effects of inhibitors and activators of protein kinase C on late erythroid progenitor (CFU-e) colony formation in vitro

Protein kinase C (PKC) plays a central role in external signal transduction for many cell types. To examine the involvement of PKC in the control of erythropoiesis, we tested the effects of PKC inhibitors on in vitro colony formation by late erythroid progenitors (CFU-e) from normal and Friend virus-infected mice. Inhibitors of PKC and other kinases (H-7 and H-8) inhibited CFU-e at concentrations which inhibit PKC. HA1004, an inhibitor of the cyclic nucleotide-dependent kinases and a weak inhibitor of PKC, had little effect on CFU-e. In the absence of erythropoietin, a combination of phorbol ester and Ca++ ionophore significantly increased normal CFU-e. These results suggest PKC plays a role in the transduction of regulatory signals for the growth of CFU-e.

DMSO induces reactivation of cytomegalovirus in vitro from spleens of latently infected mice. Brief report

Reactivation of murine cytomegalovirus in spleen explant cultures from latently infected CD 1 mice was studied. A significant increase in the incidence of reactivation was observed when 200 mM DMSO was included in the culture medium. Virus could also be reactivated from the bone marrow of some mice.

Glucocorticoid receptors and corticosensitivity in the human monocytic cell line CM-S: changes during phorbol ester-induced differentiation

CM-S is a line of human precursor mononuclear phagocytes inducible to macrophage differentiation in response to the tumor promoter phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Untreated CM-S cells expressed a single class of high-affinity (KD = 4.5 +/- 2.3 nM) glucocorticoid receptor sites (GCr) (27,530 +/- 3752 sites/cell) as measured by a whole-cell assay at 37 degrees C using [3H]triamcinolone acetonide as tracer, while CM-S cells induced to macrophage differentiation by 10(-7) M TPA showed reduced levels of GCr (10,729 +/- 2135 sites/cell). Kinetic studies indicated that this reduction was progressive, reaching about 34% of the original value 96 hr after TPA addition. The GCr in untreated and TPA-induced cells were similar in their specificity for corticosteroids. In the precursor cell population dexamethasone enhanced both the rate of protein synthesis and the production of autostimulatory growth factor(s), while in TPA-induced cells it inhibited the rate of protein synthesis in a dose-dependent manner. Our data with the CM-S cell line thus suggest that in the monocytic cell line lineage both the number of GCr and the cell response to glucocorticoids depend on the degree of cell maturation.

Phorbol esters inhibit the binding of low-density lipoproteins (LDL) to U-937 monocytelike cells

The present study demonstrates that U-937 monocytelike human cells possess specific LDL receptors. 125I-LDL binds at 4 degrees C on the cell surface. The bound molecules are releasable by heparin. The reaction requires Ca2+ and the binding sites are sensitive to proteolysis. Unlabeled LDL compete with 125I-LDL, whereas HDL are ineffective. At 37 degrees C, LDL are internalized and degraded by a chloroquine-sensitive pathway. Tumor-promoting phorbol esters inhibit the binding of 125I-LDL to its receptor on U-937 cells. This inhibition exhibits temperature, time, and concentration dependence. At 37 degrees C, inhibition is 50% at 5 X 10(-9) M of TPA. After removal of phorbol esters, treated cells recover their 125I-LDL-binding activity in 60 min. The inhibitory activities of various phorbol esters are proportional to their tumor-promoting activities. Inhibition appears to be due to a reduction in the number of available LDL receptors rather than a decrease in receptor affinity.