GTP analogues cause preferential translocation of an 18 kDa cytosolic G-protein to the membrane fraction in the ZR-75-1 human breast-cancer cell line

The novel cyclic dinucleotide 3'-5' cyclic diguanylic acid binds to p21ras and enhances DNA synthesis but not cell replication in the Molt 4 cell line

1. The effect of the novel, naturally occurring nucleotide 3'-5' cyclic diguanylic acid (c-di-GMP) on the lymphoblastoid Molt 4 cell line was studied. When exposed to this guanine nucleotide. Molt 4 cells exhibited a marked increase in [3H]thymidine incorporation, up to 200-fold at 50 microM c-di-GMP. Correspondingly, the DNA content of the treated cells was 9-fold higher than untreated cells. Stimulation of [3H]thymidine incorporation into the cells was time- and concentration-dependent. This effect was specific and was not observed with GMP or cyclic GMP, nor with the unhydrolysable GTP analogues, guanosine 5'-[gamma-thio]triphosphate and guanosine 5'-[beta gamma-imido]-triphosphate. C-di-GMP entrance into the cells was experimentally verified and occurred without using any means of cell permeabilization. SDS/PAGE analysis of cells exposed to [32P]c-di-GMP, followed by autoradiography, revealed the labelling of three low-molecular-mass proteins at 18-27 kDa. The labelling is highly specific to c-di-GMP and its extent was not affected by other guanine nucleotides. 2. One of the c-di-GMP-binding proteins was found to be the p21ras protein, by immunoprecipitation with the anti-Ras monoclonal antibody Y13-259. The effects described appear to be unique for c-di-GMP and, taken together, raise the possibility that an irreversible binding of this guanine nucleotide to the growth-promoting p21ras protein results in a fixed active conformation of this protein affecting DNA synthesis. Strikingly, although at 48 h of growth markedly high DNA levels were found in Molt 4 cells treated with c-di-GMP, this guanine nucleotide had no effect on cell replication during this period. Thus Molt 4 cells exposed to c-di-GMP enter the S phase uncoordinated with their overall replication rate.

Monoclonal antibodies against native ovarian tumor cells: specificity and characterization of the antigen. A preliminary report

Monoclonal antibodies were prepared against native human ovarian carcinoma cells derived from the ascitic fluid of a patient (BH). One antibody, HC7R7, was selected on the basis of its binding to tumor BH cells, to other ovarian tumor cell lines (CAOV-3 and GZL-8), but not to the patient's fibroblasts. One hundred cell smears from ascitic and pleural effusions of tumor-suspected patients were immunostained with HC7R7. All serous ovarian carcinomas and half of the breast carcinomas stained positive with HC7R7; cells from noncancer ovarian aspirates were negative. Mesothelial cells were also stained with HC7R7. A correlation was noted between HC7R7 and OC-125 staining of ovarian tumor cells but not between HC7R7 and c-neu staining of breast tumor paraffin sections. The location of HC7R7-positive material in ovarian tumor cell lines (CAOV-3 and GZL-8) differed from that in the breast tumor cell line (MCF-7). CAOV-3 and GZL-8 showed membrane binding while, in MCF-7, not fully identified intracellular organelles were stained. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunoblots from membrane and cytosol fractions of GZL-8 and MCF-7 showed HC7R7 binding to three protein bands in the membrane fraction and to three other bands in the cytosol, all in the 29- to 68-kDa range. Two of the bands were glycoproteins. The only band that was different in the GZL-8 and MCF-7 cells was a 43-kDa glycoprotein, which was more pronounced in the MCF-7 cells. The possible significance of the new HC7R7 antibodies for detection and survey of ovarian malignancies is discussed.

Guanine nucleotide modulation of high affinity gonadotropin-releasing hormone receptors in rat mammary tumors

We previously suggested that gonadotropin-releasing-hormone (GnRH) analogues activate the phosphoinositide pathway in rat mammary tumor membranes. In the present study we analyzed the binding of GnRH analogues to these membranes and assessed its modulation by guanine nucleotides. [125I]Buserelin (a GnRH superagonist) binding is specific because it is displaced only by GnRH analogues. Scatchard plot analysis reveals high affinity binding sites (Kd = 2.5 +/- 0.8 nM, Bmax = 250 +/- 120 fmol/mg membrane protein) and low affinity binding sites (Kd 1.1 +/- 0.3 microM, Bmax = 200 +/- 105 pmol/mg membrane protein). Guanine nucleotides increased the ED50 of [125I]buserelin displacement, and almost completely eliminated the high affinity binding. Similar results were obtained with [125I]D-Trp6-GnRH--another GnRH superagonist. The inhibition of buserelin binding by guanine nucleotides was specific for nucleotides that interact with G-binding proteins and was dose-dependent with a maximal effect at 10 microM GTP gamma S. Kinetic analysis of buserelin binding revealed that the dissociation rate increased at least 4-fold in the presence of 10 microM GTP gamma S. These results support the hypothesis that GnRH analogues interact directly with mammary tumors and activate a G-protein-dependent transducing mechanism.