Identification of semaphorin3B as a direct target of p53.

A cDNA microarray analysis indicated that Semaphorin3B (Sema3B), a gene whose product is involved in axon guidance and axonal repulsion, is inducible by p53. Introduction of exogenous p53 into a glioblastoma cell line lacking wild-type p53 (U373MG) dramatically induced expression of Sema3B mRNA. An electrophoretic mobility shift assay and a reporter assay confirmed that a potential p53 binding site present in the promoter region had p53-dependent transcriptional activity. Expression of endogenous Sema3B was induced in response to genotoxic stresses caused by adriamycin treatment or UV irradiation in a p53-dependent manner. Ectopic expression of Sema3B in p53-defective cells reduced the number of colonies in colony formation assays. These results suggest that Sema3B might play some role in regulating cell growth as a mediator of p53 tumor-suppressor activity.