Prokineticins (endocrine gland-derived vascular endothelial growth factor and BV8) in the bovine ovary: Expression and role as mitogens and survival factors for corpus luteum-derived endothelial cells

A highly vascular endocrine gland, the corpus luteum ( CL) is an excellent model for the study of angiogenic factors. Prokineticins (PK-1 and -2), also termed endocrine-gland-derived vascular endothelial growth factor ( VEGF) and BV8 are newly identified proteins described as selective angiogenic mitogens. We previously identified PK binding sites, two closely homologous G protein-coupled receptors (PK-R1 and PK-R2) in human and bovine ovarian cells, but their function remained unknown. In this study we examined the presence and effects of PK in CL-derived endothelial and steroidogenic cell types (LEC and LSC, respectively). PK-1 mRNA was identified in CL and follicles by real-time PCR, using primers specific for the bovine PK-1 sequence ( retrieved from Bos taurus whole genome shotgun database). PK were potent angiogenic mitogens for LEC; they enhanced cell proliferation, elevated [H-3] thymidine incorporation, MAPK activation, and c-jun/fos mRNA expression. The effects of PK proteins on cell survival were examined by nuclear morphology (4', 6-diamidino-2-phenylindole dihydrochloride staining), measurement of DNA fragmentation (terminal dUTP nucleotide end labeling assay), and caspase-3 cleavage. Results obtained by these techniques demonstrated that PK protected LEC from serum starvation-induced apoptosis. Stress conditions such as serum withdrawal, TNF-alpha, and hypoxia markedly increased PK-R2 expression, whereas mRNA levels of PK-R1 remained unchanged. These suggest that the antiapoptotic effect of PK-1 on LEC may be mediated via PK-R2. PK-1 increased VEGF mRNA expression by LSC, implying that it could also indirectly, via VEGF, affect luteal angiogenesis. Together, these findings suggest an important role for PK-1 in luteal function by acting as a mitogen and survival factor in LEC.