Platform Session 2. Signaling Pathways in the Ovary, Uterus, and Pituitary
Sunday, July 24, 2005
3:00 PM–5:00 PM
Location: CCQ 204AB
(12) THE NODAL-ALK7 PATHWAY INDUCES APOPTOSIS IN NORMAL OVARIAN SURFACE EPITHELIAL AND EPITHELIAL OVARIAN CANCER CELL LINES.
Xu, Guoxiong 1, Wang, Qinghua2, Peng, Chun1, 1 York University, Toronto, ON, Canada2 St. Michaelís Hospital, Toronto, ON, Canada
ABSTRACT- Epithelial ovarian cancer (EOC), arisen from the ovarian surface epithelium (OSE), is the most fatal gynaecological malignancy. The transforming growth factor-(TGF-) superfamily has been implicated in many types of cancer, including ovarian cancer. We have recently demonstrated that Nodal, a member of TGF- superfamily, acts through activin receptor-like kinase 7 (ALK7) to induce apoptosis in several EOC cell lines. In this study, we investigated whether the Nodal-ALK7 pathway also exerts an apoptotic effect in an immortalized OSE cell line, IOSE397, and the mechanisms underlying the effect of Nodal and ALK7. Nodal and its signaling molecules including ALK7, ActRIIB, and Smad 2, 3, and 4 are expressed in IOSE397 cells and in an EOC cell line, OV2008. Infection of IOSE397 and OV2008 cells with an adenoviral construct carrying constitutively active ALK7 (ALK7-ca) resulted in apoptosis in both cell lines as assessed by DAPI staining, MitoShift assay and activated caspase 3 detection. Transfection of cells with a Nodal-expressing plasmid also resulted in a significant increase in the programmed cell death. Both Nodal and ALK7-ca induced Smad2 and Smad3 phosphorylation and nuclear translocation. The activation of caspase 3 by Nodal was blocked in the presence of a dominant negative Smad4. These data indicate that the Smad pathway is involved in the Nodal-ALK7-induced apoptosis. To further determine the target genes of Nodal and ALK7, we measured Bcl-2, Bcl-XL and Bax levels by RT-PCR and Western blot. The basal level of Bcl-2 and Bcl-XL expression was higher in OV2008 than in IOSE397 cells. ALK7-ca decreased both mRNA and protein levels of anti-apoptotic factors, Bcl-2 and Bcl-XL, whereas increased the expression of pro-apoptotic factor, Bax. Xiap, a key member of inhibitor of apoptosis proteins which blocks apoptosis by inhibiting the activation and activity of caspase 3 and 9, was downregulated by ALK7-ca. Taken together, these findings demonstrate that the Nodal-ALK7-Smad pathway induces apoptosis in both normal and tumor ovarian surface epithelial cell lines and that Xiap and members of the Bcl-2 family may be involved in the apoptotic action of Nodal-ALK7 (Supported by CIHR).
KEY WORDS: Nodal, apoptosis, ovarian cancer cells, TGF-