PARENT SESSION
PLATFORM SESSION 19. PITUITARY HORMONES AND GROWTH FACTORS

Tuesday, August 3, 2004
4:30 PM–6:30 PM
Buchanan A102
Chair: Christine Quirk Co-Chair: James Dias

(588) NODAL AND ACTIVIN RECEPTOR LIKE KINASE 7(ALK7) INDUCE APOPTOSIS IN HUMAN TROPHOBLAST CELLS.

Munir, Sadia¹, Xu, Guoxiong¹, Yang, Burton², Peng, Chun ¹, ¹ Department of Biology, Toronto, ON, Canada² Sunnybrook and Women’s College Health Sciences Centre, and, Toronto, ON, Canada

ABSTRACT- Nodal is member of transforming growth factor- (TGF-) family and is known to play critical roles during vertebrate embryogenesis. Activin receptor-like kinase 7 (ALK7) is a type I receptor for Nodal. Recently, we cloned cDNAs encoding human ALK7 and its isoforms from human placenta and demonstrated their expression in human placental tissues throughout pregnancy and in cell lines derived from normal trophoblast and choriocarcinoma. These findings suggest that ALK7 may be involved in the regulation of placental development and function. In this study, we determined the effect of ALK7 and its ligand Nodal in regulating trophoblast cell apoptosis using JEG-3 cells as a model. The coding region of Nodal or ALK7 was amplified by PCR and cloned into a mammalian expression vector, pcDNA4. Constitutively active ALK7 (ALK7-ca) and a kinase defective ALK7 (ALK7-kd) were generated using site directed mutagenesis. Cells were then transiently transfected with these constructs, either alone or in combination. Forty eight hours after transfection, apoptosis was determined by Annexin V or Hoechst staining, followed by flow cytometry or manual cell counting, respectively. Overexpression of either Nodal or ALK7-ca resulted in significant increases in the number of cells undergoing apoptosis. The proapoptotic effect of Nodal was abolished when ALK7-kd was co-transfected with Nodal. These results demonstrate that Nodal acts through ALK7 to induce apoptosis in trophoblast cells. To determine the mechanisms underlying the Nodal/ALK7-induced trophoblast cell apoptosis, we examined the expression of several genes known to be involved in apoptosis. Overexpression of Nodal or ALK7-ca reduced the expression of X-link inhibitor of apoptotic protein (XIAP). Similarly, the expression of Bcl-2, another antiapoptotic protein, was inhibited by Nodal and ALK7-ca. Taken together, this study demonstrates that the Nodal-ALK7 pathway is involved in the induction of apoptosis and this effect is mediated, at least in part, by Bcl-2 and XIAP. (Supported by a CIHR grant to CP).

KEY WORDS: ALK7, trophoblast cells, Nodal, apoptosis