Prokineticins (endocrine gland-VEGF 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-glandderived VEGF and BV8 are newly identified proteins described as selective angiogenic mitogens. We previously identified PK binding sites - two closely homologous G proteincoupled 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 PKsin CL-derived endothelial and steroidogenic cell types (LEC and LSC, respectively). PK-1 mRNA were 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). PKs were potent angiogenic mitogens for LEC: they enhanced cell proliferation, elevated [3H]-thymidine incorporation, MAPK activation and c-jun/fos mRNA expression. The effects of PK proteins on cell survival were examined by nuclear morphology (DAPI staining), measurement of DNA fragmentation (TUNEL assay) and caspase-3 cleavage. Results obtained by these techniques demonstrated that PKs protected LEC from serum starvation-induced apoptosis. Stress conditions such as serum withdrawal, TNFα and hypoxia markedly increased PK-R2 expression, whereas mRNA levels of PK-R1 remained unchanged. These suggest that the anti-apoptotic 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.