Independence of normal phenotypic properties and cell surface receptor mobility in variant cell lines

We report the use of three classes of variants from the long-established malignantly transformed LM cell line to demonstrate that the apparent mobility of cell surface receptors need not be dependent on the expression of the transformed phenotype in vitro.     

4-Hydroxynonenal interacts with tubulin by reacting with its functional -SH groups

4-Hydroxynonenal, which is one of the most important products of lipid peroxidation, alters microtubular organization and structure in 3T3 fibroblasts. Changes in cell shape and the disappearance of microtubules are observed by immunofluorescence after incubation with the aldehyde, and the colchicine binding activity of tubulin from 3T3 cells is modified. Moreover, the aldehyde determines a decrease in the ability of purified tubulin to polymerize and to bind colchicine. These effects may be related to the interaction of the aldehyde with functional -SH groups of tubulin which are necessary for protein integrity and functions. Indeed, the addition of cysteine protects against the damaging effects of the aldehyde.     

Colchicine-induced polyploidy in phalaenopsis orchids

Colchicine can induce polyploidy in phalaenopsis orchids. When young protocorms are treated in liquid culture with 50 mg/l colchicine, about 50% of the protocorms develop into tetraploids.     

Microtubular protein impairment by pentanal and hexanal

Pentanal and hexanal are some of the aldehydes produced by lipid peroxidation, that causes damage to several subcellular structures. Lipoperoxidation products may directly attack cytoskeleton structures, the integrity of which is required for secretion mechanisms, e.g. 4-hydroxy-alkenals after microtubular integrity and function. Purified microtubular protein incubated with pentanal and hexanal at different concentrations revealed a tubulin-aldehyde interaction affecting the polymerization reaction and the colchicine-binding activity. These reactions apparently do not involve sulphydryl groups, and the addition of mercaptoethanol does not protect microtubules from the action of aldehydes, the effect of which is however more homogeneous, as only small differences can be noticed among the various aldehyde concentrations used.     

Studies on hepatotoxicity and toxicokinetics of colchicine

Colchicine (COL) is an alkaloid existing in plants of Liliaceous colchicum. It has widely been used in the treatments of many diseases, such as gout, Familial Mediterranean Fever, and tumor. However, the adverse effects of COL are an obstacle to its safe use. The present studies explored the role of metabolic demethylation in the development of COL‐induced hepatotoxicity. We found that inhibition of CYP3A increased the susceptibility of mice to COL hepatotoxicity, and induction of CYP3A decreased the susceptibility of animals to the hepatotoxicity. The toxicokinetic study demonstrated that pretreatment with ketoconazole caused elevated area under the concentration‐time curve of COL. Three demethylation metabolites of COL were found to be less hepatotoxic than the parent compound. It appears that the formation of electrophilic demethylation metabolites was not involved in the development of COL‐induced liver injury.     

Role of membrane colchicine binding proteins in the transmission of prolactin message to casein genes in the rabbit mammary gland

Previous work demonstrated that tubulin binding drugs specifically inhibit the capacity of prolactin to initiate casein and DNA synthesis in the mammary cell. It was concluded that microtubules or other tubulin containing cellular structures were involved in the transmission of the prolactin message to genes. In the present work, it is shown that griseofulvin, an antimitotic drug which alters microtubule structure and function, does not prevent prolactin actions. Autoradiographic studies showed that [3H]colchicine binds preferentially to plasma and Golgi membranes in the mammary cell. Short term cultures of mammary explants with [3H]colchicine demonstrated that the labelled drug binds to membranous cellular structures which were isolated from explants at the end of the culture. Fractions containing plasma and Golgi membranes contained the highest amount of radioactivity. Solubilisation of the membranes by Triton X-100 dissociated the [3H]colchicine from the prolactin receptors as judged by a chromatography of the soluble fraction on a Sepharose 6 B column. On the column, the labelled colchicine remains associated with a molecular entity which may be free tubulin. In all cases, the binding of [3H]colchicine was greatly attenuated by an excess of unlabelled colchicine but was only slightly affected by the competition with lumicolchicine. These results suggest that mammary membranes contain tubulin and that binding of drugs to this molecule inhibits the generation of the prolactin second messengers eliciting the hormonal actions in the mammary cell. This also suggests that microtubules are probably not involved in the mechanism of prolactin action.     

Cytoskeletal control of the apical surface transformation of rat uterine epithelium

Summary— During early pregnancy, in the lead up to blastocyst implantation, the apical cell surface of luminal epithelial cells of the rat uterus undergo a dramatic shape transformation. This study aims to investigate the role of the cytoskeleton in this apical transformation by considering the effects of the drugs cytochalasin D and colchicine on the uterine luminal cell surface. The results are determined using transmission and scanning electron microscopy. In vivo exposure to cytochalasin D during oestrus, as well as on day 1 of pregnancy, did not affect the long, regular surface microvilli. This drug, however, did disrupt the terminal web within the apical cytoplasm of these cells. Disruption of microfilament (MF) polymerization by cytochalasin D on day 4 of pregnancy induced a cell surface transformation, resulting in the appearance of numerous irregular projections normally present during blastocyst implantation on day 6 of pregnancy. Colchicine did not alter the uterine microvilli of oestrus or day 1 pregnant tissue. Unlike the effect of cytochalasin D, colchicine-induced microtubule (MT) disruption on day 4 of pregnancy did not increase irregular projections and hence this treatment did not result in the cell surface appearance associated with blastocyst implantation. These results indicate that the disruption of MF, rather than MT, contributes to the transformation of the uterine luminal cell surface during the lead up to blastocyst attachment.