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Characterization of cell-cycle arrest by fumonisin B1 in CV-1 cells
J R Ciacci-Zanella1, A H Merrill, E Wang
1Center for Biotechnology, Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln 68583, USA.
Abstract:
Fusarium moniliforme is a widespread fungal pathogen which primarily infects corn, but can also infect rice or wheat. Fusarium moniliforme produce several mycotoxins, the most prominent of which is called fumonisin B1 (FB1). Epidemiological studies have indicated that ingestion of fumonisins correlates with a higher incidence of oesophageal cancer in Africa and China. Fumonisins also cause a neurodegenerative disease in horses, induce hepatic cancer in rats, are nephrotoxic in rats, or cause pulmonary oedema in swine. Structurally, fumonisins resemble sphingolipids and can alter sphingolipid biosynthesis. suggesting that sphingolipid alterations play a role in disease and carcinogenesis. Previous studies determined that FB1 blocked cell-cycle progression in CV-1 cells but not COS-7 cells. Herein, we have examined the effects that FB1 treatment has on cell-cycle regulatory proteins. Our studies established that FB1 treatment of CV-1 cells, but not COS-7 cells, leads to dephosphorylation of the retinoblastoma (Rb) protein. Cyclin dependent kinase 2 (CDK2) activity was repressed five- to 10-fold and cyclin E protein levels were lower in CV-1 cells after fumonisin treatment. Two CDK inhibitors, Kip1 and Kip2, were induced within 3 hours after fumonisin treatment of CV-1 cells, suggesting these two proteins mediate cell-cycle arrest induced by FB1. This mycotoxin caused large increases in sphinganine within 3 hours after addition of FB1. As sphingoid bases are known to induce Rb phosphorylation, this increase in sphinganinie might be the stimulus for the suppression of cyclin dependent kinase activities via Kip1 and Kip2. The ability of FB1 to accumulate sphingosine or sphinganine and arrest the cell cycle in some cells but not others may play an important role in carcinogenesis or disease.
Insights
Fumonisin B1 (FB1), a mycotoxin from Fusarium moniliforme, disrupts cell-cycle regulation by altering sphingolipid biosynthesis. This disruption leads to cell-cycle arrest in some cells, potentially contributing to diseases like cancer.
Area of Science:
- Mycology
- Toxicology
- Cell Biology
Background:
- Fusarium moniliforme is a fungal pathogen producing fumonisin B1 (FB1).
- FB1 is linked to oesophageal cancer in humans and various toxicities in animals.
- Fumonisins structurally mimic sphingolipids, suggesting a role in sphingolipid metabolism disruption.
Purpose of the Study:
- To investigate the effects of FB1 on cell-cycle regulatory proteins.
- To elucidate the mechanism by which FB1 affects cell-cycle progression.
- To understand why FB1 impacts certain cell types (CV-1) but not others (COS-7).
Main Methods:
- Treatment of CV-1 and COS-7 cells with FB1.
- Analysis of retinoblastoma (Rb) protein phosphorylation status.
- Assay of Cyclin Dependent Kinase 2 (CDK2) activity.
- Quantification of cyclin E protein levels.
- Measurement of CDK inhibitors Kip1 and Kip2.
- Assessment of intracellular sphinganine levels.
Main Results:
- FB1 treatment caused dephosphorylation of Rb protein in CV-1 cells, but not COS-7 cells.
- CDK2 activity was significantly repressed, and cyclin E levels decreased in FB1-treated CV-1 cells.
- Kip1 and Kip2 expression was induced within 3 hours of FB1 exposure in CV-1 cells.
- FB1 treatment led to a substantial increase in sphinganine levels in CV-1 cells.
- FB1's effects on cell-cycle arrest were cell-type specific.
Conclusions:
- FB1-induced alterations in sphingolipid biosynthesis, specifically increased sphinganine, likely mediate cell-cycle arrest in susceptible cells.
- The induction of Kip1 and Kip2 appears to be a key mechanism for FB1-induced cell-cycle arrest.
- The differential response of cell types to FB1 may be crucial for understanding its role in disease and carcinogenesis.