p73 is a novel gene that has high sequence homology and similar gene struct
ure to the tumor suppressor gene p53, We analysed p73 in seven ovarian carc
inoma cell Lines and a total of 63 human borderline and invasive ovarian tu
mor samples. Loss of heterozygosity at this locus was observed in 50% of in
vasive tumors but in none of the borderline tumors. Biallelic expression of
the gene was observed in the heterozygous tumor tissues. Direct sequencing
and single-strand conformation polymorphism analyses of the p73 cDNA seque
nce homologous to the highly mutatable region of p53 did not reveal any mut
ations. When compared to the primary cultures of normal human ovarian surfa
ce epithelial cells and immortalized cell lines, four of the seven ovarian
carcinoma cell lines, 71% of the invasive tumors, and 92% of the borderline
tumor tissues express elevated levels of p73 transcript. Except for the OV
CA3 cell line, Western blot analysis of the nuclear extracts prepared from
the cell lines showed concordant levels of p73 protein. Our analysis also d
emonstrated the expression of a spliced variant of p73 transcript with the
omission of exon 2 solely in the cancer cell lines and invasive tumor tissu
es. This exon 2-spliced transcript would give rise to a truncated p73 prote
in without the N-terminal transactivation domain. In reminiscence of the do
minant negative phenotype of the N-terminal truncated variants of another p
53-related gene, p63, the expression of the truncated p73 variant form in o
varian tumors may play an important role in the pathogenesis of ovarian can
cer.