ENDOMETRIOTIC LESIONS SYNTHESIZE AND SECRETE A HAPTOGLOBIN-LIKE PROTEIN

To explore the identity and possible function of endometriosis protein -I (ENDO-I), which is an acidic glycoprotein synthesized and secreted by endometriotic lesions, partial amino acid sequence and cDNA sequenc e were determined. Partially purified, de novo-synthesized rat endomet riosis glycoproteins were separated by two-dimensional SOS-PAGE, trans ferred to polyvinyl difluoride membranes, and stained with Coomassie b lue. Protein corresponding to the size and pi of ENDO-I was cut from t he membranes and analyzed by automated Edman degradation. ENDO-I amino acid sequence analysis identified 15 residues that shared significant homology with the beta-chain of rat, mouse, and human haptoglobin (Hp ) and human Hp-related protein. Western blot analyses using anti-Hp an tibody demonstrated cross-reactivity with de novo-synthesized ENDO-I p rotein in endometriosis culture media. For nucleotide sequence analysi s, poly A-enriched mRNA was isolated from rat endometriotic tissues. A gene-specific oligonucleotide primer was designed and used for 3' rap id amplification of cDNA ends (RACE). Automated sequencing of RACE cDN A fragments identified 859 base pairs, of which 858 were identical to rat Hp. Reverse transcription-polymerase chain reaction was used to de monstrate that ENDO-I transcripts are differentially expressed by endo metriosis but not by uterine tissues. In the human, distinct subtypes of Hp as well as proteins sharing epitopes with Hp have been used to d iagnose a variety of diseases; therefore, Hp-like ENDO-I may prove to be a nonsurgical diagnostic tool to assess endometriosis. Hepatic Hp, induced by acute-phase stimuli, modulates macrophage function and angi ogenic activity. If ENDO-I possesses similar activities, it may be inv olved with anomalies of the immune system or the etiology and pathophy siology of endometriosis.