monensin and Fibrosarcoma

The present study was designed to identify, submicroscopically, the primary organelle or target structure for monensin in cultured murine fibroblasts L929. In addition, the effect of the drug on cell size and surface membranes of the cells were analysed; cellular proliferation, collagen secretion, and necrosis and apoptosis were re-evaluated. At the lowest concentration of monensin the foremost ultrastructural alteration occurred in the mitochondria, characterized by increased matrix density with disorganized and less distinct crystae. Incubation with monensin at higher concentrations resulted in severe mitochondrial damage and marked dilatation of the Golgi apparatus and rough endoplasmic reticulum cisternae. Fibroblasts exposed to higher concentrations of monensin were enlarged with decreased number of filopodia and hollows in the surface membrane. Moreover, monensin inhibited the cell proliferation, increased immunohistochemical positiveness for collagen type I in a dose-dependent manner, and, at high concentrations, caused cell necrosis whereas apoptosis was not induced. Taken together, these results show that monensin induces early mitochondrial damage, possibly causing an energy deficit that led to inhibition of fibroblasts proliferation and accumulation of collagen causing dilatation of Golgi apparatus and rough endoplasmic reticulum. Moreover, the mitochondrial damage would also explain the monensin-induced necrosis.

Topics: Animals; Cell Proliferation; Dose-Response Relationship, Drug; Endoplasmic Reticulum; Fibroblasts; Fibrosarcoma; Golgi Apparatus; Immunohistochemistry; Mice; Microscopy, Electron; Mitochondria; Monensin

Hyaluronate-containing pericellular coats have been demonstrated around rat fibrosarcoma cells by exclusion of particles (fixed red blood cells). The cell coats normally form during spreading of the rat fibrosarcoma cells subsequent to subculturing. Monensin, a drug which disrupts the Golgi and which also inhibits hyaluronate synthesis in these cells, inhibits the regeneration of these coats after hyaluronidase or trypsin treatment but does not inhibit cell spreading. Cycloheximide, a drug which inhibits protein but not hyaluronate synthesis does not prevent coat regeneration but partially inhibits cell spreading. Thus by exploiting the opposing effects of cycloheximide and monensin on coat regeneration and cell spreading, we have been able to dissociate these two phenomena.

Topics: Animals; Cell Adhesion; Cells, Cultured; Cycloheximide; Extracellular Space; Fibrosarcoma; Hyaluronic Acid; Monensin; Rats

Evidence is presented that monensin-sensitive membranes, presumably the Golgi apparatus, are involved in the synthesis of hyaluronate in rat fibrosarcoma cells. Monensin caused the inhibition of incorporation of metabolic precursors into hyaluronate produced by rat fibrosarcoma cells in a concentration- and time-dependent manner. Maximum inhibition (70-80%) was obtained on treatment with 10(-7) M monensin for 24 h. Incorporation of label into secreted hyaluronate and into that associated with the cell surface was inhibited, but incorporation into intracellular hyaluronate was not inhibited. In 3T3 cells, treatment for 24 h with 10(-7) M monensin inhibited incorporation of label only into secreted hyaluronate. The hyaluronate-rich pericellular coat, revealed by exclusion of fixed red blood cells, was depleted on treatment with monensin under the same conditions which caused inhibition of hyaluronate synthesis in the fibrosarcoma cells. Cell proliferation, as measured by DNA content/culture and [3H]thymidine incorporation, was also inhibited in a dose-dependent manner by monensin (10(-8)-10(-6) M). Protein synthesis was not inhibited at these doses, nor was monensin cytotoxic as judged by a 51Cr release assay. The inhibition of hyaluronate synthesis was independent of the antiproliferative effect of monensin because it was obtained during log phase growth or confluency and in the presence or in the absence of serum.

Topics: Animals; Cell Line; Cells, Cultured; Fibrosarcoma; Furans; Hyaluronic Acid; Kinetics; Monensin; Rats; Sarcoma, Experimental