Fibulin-1 is an extracellular matrix protein induced by estradiol in estrogen receptor (ER) positive ovarian cancer cell lines. Alternative splicing of ®bulin-1 mRNA results in four di erent variants named A, B, C and D that may have distinct biological functions. We studied the relative expression of ®bulin-1 mRNA variants and their estrogen regulation in human ovarian cancer cells. In ovarian tissues and cancer cell lines, ®bulin-1C and -1D are the predominant forms, whereas ®bulin-1A and -1B are weakly expressed. We developed a competitive PCR assay based on coampli®cation of ®bulin-1C and -1D to study the relative expression of these ®bulin-1 variants in human ovarian samples. In ovarian cancer cell lines and ovarian cancer samples, there was a marked increase in the ®bulin-1C:1D and ®bulin-1C:HPRT mRNA ratios as compared to normal ovaries. In the BG1 estrogen receptor positive ovarian cancer cell line, ®bulin-1C mRNA was induced by estradiol in a dose-and time-dependent manner. Since others and we have previously shown an increased expression of ERa as compared to ERb in ovarian cancer cells, we investigated whether ERa or ERb is involved in this induction. For this aim, MDA-MB-231 breast cancer cell line, which expresses both low basal levels of ERs and ®bulin-1, was infected with recombinant ERa or ERb encoding adenovirus and treated with estradiol. Fibulin-1C was induced by estradiol in ERa-but not ERb-infected cells, suggesting that ®bulin-1C induction is mediated through ERa. In ovarian tumors, a trend towards a correlation between ®bulin-1C and ERa expression levels was noted. In conclusion, this study showed an increased ®bulin-1C: -1D mRNA ratio in ovarian cancer cells as compared to normal ovaries. This ®nding suggests that the C variant may be involved in ovarian carcinogenesis. Fibulin-1C overexpression may thus be a clue for the understanding of a putative role of estrogens in ERa promoted ovarian tumor progression.

Fibulin-1 is an extracellular matrix protein overexpressed in epithelial ovarian and breast cancers. In estrogen receptor (ER)-positive ovarian and breast cancer cell lines, fibulin-1 mRNA levels are markedly increased by estrogens. Transfection experiments using fibulin-1 promoter constructs indicate that 17beta-estradiol (E2) increases fibulin-1 gene transcription and that ERalpha is more potent than ERbeta to mediate E2 regulation of the transfected fibulin-1 promoter. Using SL2 cells devoid of specificity protein 1 (Sp1) and site-directed mutagenesis of GC boxes, we evidenced that the E2 regulation occurs through a proximal specificity protein 1 binding site. In addition, we show that fibulin-1C and -1D mRNAs, the two major fibulin-1 splicing variants, are differentially induced by E2. The induction of both mRNAs variants is direct and independent of a newly synthesized protein intermediate. Interestingly, actinomycin D chase experiments demonstrate that E2 treatment selectively shortens the fibulin-1D mRNA half-life. This indicates that estrogens affect differentially the stability of fibulin-1 variants and may explain the lower accumulation of fibulin-1D mRNA on E2 treatment. In conclusion, our data show that estrogens, via ERalpha, are key regulators of fibulin-1 expression at both the transcriptional and posttranscriptional levels. The preferential induction of the fibulin-1C variant, which is overexpressed in ovarian and breast cancer, might play an important role in estrogen-promoted carcinogenesis.

Ovarian cancers mostly derive from the monolayer epithelium that covers the ovary. There are currently very few molecular clues to the etiology of this cancer. Bone morphogenetic proteins (BMPs) are required for follicular development and female fertility and are expressed in the ovarian surface epithelium (OSE). We previously reported the expression of human chordin (CHRD), a BMP extracellular regulator, in the ovary. Here we show that CHRD is underexpressed in epithelium ovary cancer and epithelial cancer cell lines as compared with normal tissues and OSE, respectively. Besides, we detected BMP expression in all ovarian cell lines analyzed. To determine the functional relevance of the absence of CHRD mRNA in tumors and cancer cell lines, we studied the effects of CHRD on two cancer cell lines, BG1 and PEO14. Migratory and invasive properties were greatly reduced, whereas cell adhesion to the support was enhanced. In addition, we detected chordin (Chrd) expression in OSE of rat ovaries in a pattern similar to that of BMP4. Altogether, these results suggest that CHRD could participate in regulating BMP activity in normal OSE physiology, and that its mis-expression in OSE may facilitate cancer incidence and/or progression.