Cell-cycle gene expression in lovastatin-induced medulloblastoma apoptosis

3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a key rate-limiting enzyme in the mevalonate pathway, which generates precursors both for cholesterol biosynthesis and for the production of nonsteroidal mevalonate derivatives that are involved in a number of growth-regulatory processes. We have reported that lovastatin, a competitive inhibitor of HMG-CoA reductase, not only inhibits medulloblastoma proliferation in vitro, but also induces near-complete cell death via apoptosis. The mechanism of this phenomenon is unclear. Possible involvement of changes in expression of certain cell-cycle related genes led us to study some of them in more detail.

Medulloblastoma cell lines were exposed in vitro to lovastatin, and the effects of gene expression changes were studied using RT-PCR, antisense oligonucleotide, DNA electrophoresis and Western blotting analysis.

1) Levels of total Ras gene mRNA and individual Ras gene mRNA are stable in lovastatin treatment in all examined medulloblastoma cell lines. 2) Blocking c-myc gene over-expression does not enhance medulloblastoma cell sensitivity to lovastatin. 3) Following lovastatin treatment, p16 expression exhibits no change, but pronounced increases of p27KIP1 protein are observed in all examined cell lines. Lovastatin induces pronounced increases of p21WAF1 protein only in Daoy and UW228, but not in D283 Med and D341 Med. 4) Following lovastatin treatment, increased p53 protein is detected only in D341 Med, and bax protein is unchanged in all cell lines.

Lovastatin-induced growth inhibition and apoptosis in medulloblastoma are not dependent on the regulation of Ras and c-myc gene expression, but may be mediated by p27KIP1 gene expression. Lovastatin-induced apoptosis in medulloblastoma is probably p53 independent, but p53 and p21WAF1 gene expression may also mediate anti-proliferative effects of lovastatin on specific medulloblastoma cell lines.