POLYUBIQUITIN UP-REGULATION IN CORPORA-LUTEA OF PROSTAGLANDIN-TREATEDEWES

Genes that encode mRNAs for ubiquitin are activated by cells in metabo lic distress. Cytosolic proteins that consequently become conjugated t o ubiquitin are targeted for degradation. We hypothesized that ubiquit in mediates the endocrine demise of the corpus luteum induced by prost aglandin (PG) F-2 alpha. Indeed, polyubiquitin gene expression increas ed abruptly (within 2 h) in luteal tissues of ewes treated with PGF(2) alpha - before the precipitous decline in glandular progesterone accu mulation indicative of functional luteolysis. A corresponding elevatio n in ubiquitin immunostaining was localized to large (PG-sensitive) lu teal cells. It is suggested that luteal progesterone biosynthesis is d isrupted by ubiquitination of steroidogenic regulatory proteins - perh aps those involved in the mechanics of mitochondrial delivery and side -chain cleavage of cholesterol.