Levels of the KAI1 metastasis suppressor are reduced in advanced stages of many human cancers, leading to the loss of KAI1 function. A recent study has suggested that the loss of KAI1 function may also occur via alternative splicing of KAI1 mRNA which deletes an exon encoding a critical 28 amino acids from the protein. Using PCR, 20 bladder tumours at differing stage and grade, a non-tumourigenic urothelial cell line (SV-HUC-1) and 17 bladder cancer cell lines were examined for expression of this alternatively spliced (AS) KAI1 mRNA. Full-length KAI1 mRNA was present in all tumour samples and low levels of AS KAI1 mRNA in 15/20 samples. There was no association between the presence or absence of AS mRNA and clinicopathological characteristics of these tumours. Low levels of AS KAI1 mRNA were present in SV-HUC-1 and 14/17 bladder cancer cell lines. There was no association between the presence or absence of AS KAI1 mRNA and tumourigenicity, or in vivo invasive abilities of these cell lines. In all cell lines expressing AS KAI1 mRNA, levels were 3- to 5-fold lower than levels of wild-type mRNA, irrespective of wild-type mRNA levels. Low levels of an alternatively spliced form of KAI1 mRNA are present in most bladder cancer tumours and tumour cell lines, but are not associated with invasive behaviour.

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