epidermal-growth-factor and inostamycin

The addition of serum to quiescent normal rat kidney (NRK) cells induced phosphatidylinositol (PI) synthesis after 4 h and DNA synthesis after 16 h. Inostamycin, an inhibitor of CDP-DG:inositol transferase, added within 4 h, inhibited both the serum-induced PI synthesis and S phase entry. By contrast, inostamycin added 8 h after release from quiescence did not inhibit the S phase entry. Inostamycin did not affect the G2/M/G1 transition, and incubation with inostamycin induced cell synchronization at early G1 phase. Thus, PI synthesis is involved in the regulation of S phase induction.

Topics: Animals; Anti-Bacterial Agents; Bombesin; Cell Cycle; Cell Line; DNA; Epidermal Growth Factor; Furans; Homeostasis; Inositol Phosphates; Insulin; Kidney; Kinetics; Phosphatidylinositols; Platelet-Derived Growth Factor; Rats; S Phase; Streptomyces; Time Factors

Inostamycin, a novel microbial secondary metabolite, inhibited [3H]inositol and 32P1 incorporation into phosphatidylinositol (PtdIns) induced by epidermal growth factor (EGF) in cultured A431 cells, the IC50 being 0.5 micrograms/ml, without inhibiting macromolecular synthesis. The drug inhibited cellular inositol phosphate formation only when it was added at the same time as labeled inositol. It was found to inhibit in vitro CDP-DG:inositol transferase activity of the A431 cell membrane, the IC50 being about 0.02 micrograms/ml. It did not inhibit tyrosine kinase, PtdIns phospholipase C, or PtdIns kinase. Therefore, inhibition of PtdIns turnover by inostamycin must be due to the inhibition of CDP-DG:inositol transferase. Thus, inostamycin is a novel inhibitor of CDP-DG:inositol transferase.

Topics: Anti-Bacterial Agents; CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; Cell Line; Cell Membrane; Epidermal Growth Factor; Furans; Inositol; Phosphatidylinositols; Phospholipids; Phosphotransferases; Transferases (Other Substituted Phosphate Groups); Type C Phospholipases

Expression of epidermal growth factor (EGF) receptor is often increased in various human carcinomas. Therefore, inhibition of the EGF/EGF receptor-induced signaling pathway may help to suppress these carcinomas. In the presence of Ca2+, EGF induces elongation of A431 cells in approximately 30 min. The cell elongation was shown to be accompanied by a reorganization of actin filaments. These phenotypical changes were specifically inhibited by a tyrosine kinase inhibitor, erbstatin, and inhibitors of phosphatidylinositol (PI) turnover such as psi-tectorigenin and inostamycin. The amount of filamentous actin was increased by EGF, which was also inhibited by these compounds. Long-term treatment of A431 cells with EGF induced the disappearance of cytoskeleton and aggregation of the cells, which was again inhibited by the PI turnover inhibitors. Thus tyrosine kinase and phosphatidylinositol turnover inhibitors were shown to inhibit the signaling pathways of EGF-induced cytoskeletal organization of A431 cells.

Topics: Actins; Calcium; Carcinoma; Cell Aggregation; Cytoskeleton; Epidermal Growth Factor; Furans; Humans; Hydroquinones; Isoflavones; Microscopy, Phase-Contrast; Phosphatidylinositols; Protein-Tyrosine Kinases; Tumor Cells, Cultured