Down-regulation of CD44 expression in human prostatic carcinoma cell linesis correlated with DNA hypermethylation

Down-regulation of the cell-surface adhesion molecule CD44 has been suggest ed to play an important role in tumor progression and metastasis of prostat e cancer. CD44 is encoded by a gene that contains a CpG-rich region (CpG is land) in its 5' regulatory sequence. We tried to assess whether hypermethyl ation of this region is the mechanism responsible for CD44 transcriptional inactivation. A panel of prostatic-carcinoma cell lines, Du 145, LNCaP, PC3 , PC346C and TSU, was analyzed for CD44 mRNA and protein expression. Du 145 , PC3 and TSU were positive for CD44, whereas in LNCaP and PC346C both CD44 mRNA and protein expression was suppressed. Methylation-sensitive restrict ion-enzyme analysis of genomic DNA showed that, in contrast to the CD44-pos itive cell lines, the CD44-negative lines were hypermethylated in the CD44 promoter CpG island. Furthermore, treatment of a PC346C culture with the de methylating agent 5-azacytidine resulted in re-expression of CD44 mRNA. It is concluded that hypermethylation of the CD44 5' promoter region is one of the mechanisms by which CD44 expression is down-regulated in prostatic-car cinoma cell lines. (C) 1999 Wiley-Liss, Inc.