Previous studies indicated that a new member of the human
kallikrein (KLK) gene family, KLK4, was expressed in prostate, breast, and
endometrial carcinoma cell lines and may have potential as a
tumor marker. The aim of this study was to examine the expression of KLK4 in the normal ovary and ovarian
tumors of different histology, stage, and differentiation and to determine its association with ovarian
tumor progression. Using reverse transcription-PCR, Southern blot, and densitometry analyses, we found the level of KLK4 expression was higher in late stage serous (SER) epithelial-derived ovarian
carcinomas than in normal ovaries, mucinous epithelial
tumors, and
granulosa cell tumors. KLK4 was highly expressed in all of the SER ovarian
carcinoma cell lines (eight of eight), SER epithelial
carcinomas (11 of 11), and two
adenomas, whereas it was expressed at a lower level (or not at all) in normal ovaries (four of six), mucinous epithelial
tumors (three of four),
endometrioid carcinomas (four of five), clear cell
carcinomas (two of three), or
granulosa cell tumors (three of six). Of particular interest, KLK4
mRNA variants were detected in SER ovarian
carcinoma cell lines and primary cultured ovarian
tumor cells, but they were not present in normal ovaries. In situ hybridization analysis showed that KLK4
mRNA transcripts are localized to
adenocarcinoma cells of ovarian
tumor tissues. Similarly, immunohistochemical staining of ovarian
carcinoma sections showed immunoreactivity to
KLK4 protein product (hK4) antipeptide
antibodies. In addition, intracellular hK4 levels, as detected on Western blot analysis, were induced by 100 nM
estrogen treatment of the
estrogen receptor positive ovarian
carcinoma cell line OVCAR-3, >8-24 h. Our results show that the level of KLK4 expression and expression of KLK4
mRNA variants are associated with progression of
ovarian cancer, particularly late stage SER
adenocarcinomas. Moreover, hK4 may be a candidate marker for the diagnosis and/or monitoring of
ovarian epithelial carcinomas.