Mitotic aberrations induced by carbaryl reflect tyrosine kinase inhibition with coincident up-regulation of serine/threonine protein phosphatase activity: implications for coordination of karyokinesis and cytokinesis.
The insecticide carbaryl and its metabolite 1-naphthol cause partial uncoupling of karyokinesis and cytokinesis in V79 Chinese hamster fibroblasts; karyokinesis is blocked in metaphase, the microtubules of the spindle depolymerize and the chromosomes and spindle remnants become displaced to the periphery of the cell. A high frequency of these disturbed cells elongate and a smaller fraction initiate a cleavage furrow. Here, we attempt to determine the potential targets for carbaryl and 1-naphthol in cytokinesis-specific signalling, led by the fact that the potential protein phosphatase inhibitor 1-naphthyl phosphate was previously identified in treated cells. We found that the typical cytological pattern induced by carbaryl and 1-naphthol could be obtained with tyrphostins, specific tyrosine kinase inhibitors, indicating that the carbaryl-induced effects could be due to tyrosine kinase inhibition. This was confirmed by tyrosine kinase assays showing that carbaryl, 1-naphthol and 2-naphthol were equally efficient at inhibiting tyrosine kinase activity as tyrphostin B44(-). As tyrosine kinases can act as regulatory factors in determining dephosphorylation rates, the activities of type-1 (PP1) and type-2A (PP2A) serine/threonine protein phosphatases were also determined. There was a clear up-regulation of the overall PP1/PP2A activities in cells treated with carbaryl, 1-naphthol or tyrphostin B44(-). This stimulation was shown to be indirect because these compounds had no effect on the activity of purified human PP1 in the test tube. 2-Naphthol, which has been found to be less efficient with regard to displacement of chromatin, did not cause up-regulation, but a significant decrease in PP1/PP2A activity. We suggest that a net decrease in tyrosine kinase activity in combination with a net increase in PP1/PP2A activity is a precondition for cell elongation and cytokinesis in mammalian cells and that the corresponding enzymes are targets in the network of activities serving to coordinate karyokinesis and cytokinesis.
Renglin
A
A
Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University, Sweden.
Härmälä-Brasken
A S
AS
Eriksson
J E
JE
Onfelt
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D012721:Carbaryl / Q000494:pharmacology*; D002273:Carcinogens / Q000494:pharmacology; D002455:Cell Division; D002869:Chromosome Aberrations; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D051379:Mice; D052998:Microcystins; D008870:Microtubules / Q000187:drug effects; D008938:Mitosis / Q000187:drug effects*; D009284:Naphthols / Q000494:pharmacology; D019319:Okadaic Acid / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D013997:Time Factors; D020032:Tyrphostins / Q000494:pharmacology; D015854:Up-Regulation
D002273:Carcinogens; D052998:Microcystins; D009284:Naphthols; D010456:Peptides, Cyclic; D020032:Tyrphostins; D019319:Okadaic Acid; C029350:1-naphthol; C078588:microcystin; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases; D010749:Phosphoprotein Phosphatases; C028405:2-naphthol; D012721:Carbaryl