Induction of p21 (CIP1/WAF1/SID1) by estradiol in a breast epithelial cell line transfected with the recombinant estrogen receptor gene: a possible mechanism for a negative regulatory role of estradiol

Estrogens stimulate the growth of a majority of estrogen receptor (ER)-positive breast cancer cells. In contrast, estradiol exerted a 75% inhibition of DNA synthesis in the MCF-10AE(wt5) cell line, obtained by the transfection of the ER gene into a normal breast epithelial cell line, MCF-10A. The estradiol-mediated growth inhibitory effect was reversed by ICI 164384, a pure anti-estrogen. Analysis of cell cycle by flow cytometry showed a significant increase of G1 cells by estradiol treatment compared to controls. To understand the mechanism of action of estradiol on MCF-10AE(wt5) cells, we examined the level of a cyclin dependent kinase inhibitor (CKI), p21, by Western blot analysis. Our results showed a 5- to 10-fold increase in the level of p21 in estradiol-treated MCF-10AE(wt5) cells compared to controls. ICI 164384 reversed estradiol-mediated induction of p21. Northern blot analysis of p21 mRNA indicated that estradiol stimulated its message in MCF-10AE(wt5) cells. Analysis of a panel of 6 breast cancer cell lines showed the absence of p21 protein, whereas it was present at a very low level in MCF-10A cells. Comparison of p21 in MCF-10A and MCF-10AE(wt5) cells showed an abundance of p21 in the ER-transfected cells. However, this p21 appears to be inactive in the absence of estradiol. These results suggest a p21-mediated pathway as a possible mechanism for the growth inhibitory effects of estradiol on at least a subset of ER-transfected cell lines.

Differential role of transforming growth factor-alpha in two human colon-carcinoma cell lines

Antibodies to epidermal-growth-factor receptor (EGF) and transforming growth factor-alpha (TGF-alpha) were used to determine the role of endogenous TGF-alpha in the growth of 2 human colon-carcinoma cell lines. Both the GEO and HCT 116 colon-carcinoma cell lines secrete similar levels of TGF-alpha and have similar numbers of low-affinity binding sites for EGF. However, the HCT 116 cells lack the high-affinity EGF binding site present on the GEO cells. The anti-EGF receptor antibodies effectively blocked the binding of 125I-EGF to the GEO and HCT 116 cell lines. Growth of the GEO cell line was inhibited 50-80% by the anti-EGF receptor and anti-TGF-alpha antibodies. When the same antibodies, in sufficient amounts to block binding of TGF-alpha to the cells, were added to the HCT 116 cell line, no effect on growth was seen. These results suggest that while the GEO cell line utilizes TGF-alpha in an autocrine manner, the TGF-alpha secreted by the HCT 116 cells apparently does not play a role in the growth of these cells.

Characterization of the synergistic effect of insulin and transferrin and the regulation of their receptors on a human colon carcinoma cell line

The human colon carcinoma cell line, HCT 116, can be grown in chemically defined media in the absence of exogenous growth factors. The addition of transferrin and insulin will significantly stimulate growth. The interaction of these growth factors with their receptors was studied to determine whether the synergistic action of insulin and transferrin on growth involved alterations in the growth-factor receptors. Redistribution of the transferrin receptor occurred in the presence of transferrin or transferrin plus insulin. The presence of insulin in the growth media resulted in occupation of cell-surface insulin receptors without a reduction in total insulin binding. Addition of transferrin with insulin resulted in a decrease in insulin binding to its receptor, with no alteration in receptor affinity. It appears that transferrin plays a role in regulating the insulin receptor and that this may contribute to the synergistic effect of insulin and transferrin on growth.

Modulation of a high molecular weight form of transforming growth factor-alpha in human colon carcinoma cell lines

The secretion of transforming growth factor-alpha (TGF-alpha) by several human colon carcinoma cell lines in tissue culture medium was examined. All of the cell lines tested secreted TGF-alpha to varying degrees. Bio-Gel P-30 chromatography of the conditioned media from three of these cell lines (HCT 116, MOSER, FET) indicated differences in the molecular weights of secreted TGF-alpha. In the HCT 116 cell line, the majority of the TGF-like activity had a molecular weight of less than 10,000. For both MOSER and FET cell lines, 20-30% of the TGF-like activity had a molecular weight greater than 15,000. When HCT 116 and MOSER cells were treated with differentiation inducing agents there was an increase in a TGF-alpha species whose molecular weight was greater than 20,000. This indicates a possible alteration in either the processing of the TGF-alpha precursor and/or secretion of precursor products by the different cell lines.

Phosphorylation of deoxyguanosine in intact and fractured mitochondria

The phosphorylation of deoxyguanosine was measured in fractured and intact mitochondria and an apparent Km of 16 microM for deoxyguanosine was calculated using fractured mitochondria. The effects of various deoxynucleotides on the phosphorylating activity in fractured organelles was tested at both a high and low ratio of NXP/ATP and at two pH values, 7.0 and 5.5. Exogenous dGTP, dGDP or dITP were inhibitory under all conditions tested. With a NXP/ATP ratio of 0.08 at pH 7.0, TTP, TDP, dADP, ADP, UTP and UDP were stimulatory, but at pH 5.5 only TTP elicited that response. When the NXP/ATP ratio was 10 at pH 5.5, TTP and UTP increased the activity more than 10-fold, whereas, at pH 7.0 TTP, TDP, dADP, ADP, UTP, UDP caused stimulation, but to a much lesser extent. When exogenous Mg2+, Mn2+ or Ca2+ were added to intact mitochondria, the rates of phosphorylation were lowered. In fractured mitochondria in the absence of exogenous ATP, little phosphorylation occurs, hence these metal ions caused little change. ATP-Mg, ATP-Mn and ATP-Ca, each at 0.05 mM caused a small inhibition with intact mitochondria, whereas, these compounds supported phosphorylation with fractured organelles. ATP-Mn (10 mM) or ATP-Ca (10 mM) stimulated phosphorylation in both intact and fractured mitochondria. Intact mitochondria synthesized dGMP, dGDP and dGTP when metal ion or ATP-Me concentrations were low (0.05 mM) or when Mg2+ concentration was high (10 mM). Additions of ATP-Ca, ATP-Mn, ATP-Mg, Mn2+ or Ca2+ at 10 mM cause the loss of dGDP and dGTP formation and, in most cases, an increase in the synthesis of dGMP.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolism of deoxyguanosine in mitochondria. Characterization of the uptake process

The uptake of deoxyguanosine by rat liver mitochondria was characterized. The process required an intact mitochondrial membrane and exhibited a dependence on added phosphate. Deoxyguanosine uptake was minimally influenced by Mg2+ or Mn2+, but Ca2+ at concentrations above 0.5 mM were detrimental. Of the deoxynucleosides tested, only deoxyinosine inhibited the uptake of deoxyguanosine. The ribonucleoside guanosine was not observed to compete with its deoxynucleoside analog. Known inhibitors of nucleoside transport, cytochalasin B and NBMPR, did not block deoxyguanosine uptake, but the sulfhydryl reagents NEM and pCMB were both inhibitory. The uptake of deoxyguanosine was shown to be a saturable process and an apparent Km of 0.64 microM was calculated from a Hanes plot.

The metabolism of deoxyguanosine in mitochondria: relationship of the uptake of deoxyguanosine to the electron transport chain and adenosine triphosphate

That deoxyguanosine is taken up by isolated rat liver mitochondria has been shown. This report describes the relationship between that uptake and oxidative phosphorylation. By measuring this process in the presence of standard inhibitors of oxidative phosphorylation it was determined that a functional electron transport chain, but not the phosphorylation of ADP, was essential for uptake. ATP analogs adenyl(beta,gamma-methylene)diphosphate and adenylimidodiphosphate blocked uptake, indicating that ATP hydrolysis was required. ADP also proved to be an inhibitor. Exogenous UTP slightly stimulated deoxyguanosine uptake, as did added ATP, but several other nucleotides (dGTP, dATP, UDP, dGDP) were inhibitory. A sulfhydryl group was important for deoxyguanosine uptake and inhibition of uptake by N-ethylmaleimide was protected by both deoxyguanosine and ATP. These data show that deoxyguanosine uptake by mitochondria is a process which is coordinated and, perhaps, regulated by other events which take place in the organelle.

The metabolism of deoxyguanosine in mitochondria: a characterization of the phosphorylation process which occurs in intact mitochondria

Isolated, intact mitochondria were evaluated for their ability to phosphorylate deoxyguanosine. This activity was stimulated by exogenous ATP, substrates for oxidative phosphorylation or added inorganic phosphate. Inhibitors of oxidative phosphorylation lowered the levels of deoxyguanosine phosphorylation. From a Hanes plot, an apparent Km of 0.83 microM deoxyguanosine was calculated for the phosphorylation activity in intact mitochondria. In the presence of a 20-fold excess of added deoxynucleosides, none of those tested were strongly inhibitory. However, added UDP and dTDP were stimulatory and dGTP and dGDP were inhibitory to the phosphorylation of deoxyguanosine. These data show that mitochondria phosphorylate deoxyguanosine and that the process is regulated by other events which take place within the organelle.