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.