Steroidogenesis-inducing protein (SIP) stimulates endometrial matrix metalloproteinase-3 (MMP-3) expression and antagonizes progesterone-mediated suppression of this enzyme.

Abstract

Objective: The regulation of ectopic cell growth and tissue invasion during establishment of endometriosis is complex and poorly understood. Although endometriosis is largely dependent on steroid action, a recently identified ovarian protein may also play a role in this disease. SIP, isolated from human follicular fluid, stimulates mitochondrial conversion of cholesterol to pregnenelone and is a potent stimulator of cell proliferation and DNA synthesis. The release of SIP into the peritoneal environment at ovulation could play an important role(s) in enhancing ectopic endometrial growth. In the current study, we investigated the ability of SIP to stimulate expression of MMP-3, a stromal-specific enzyme implicated in numerous invasive diseases, including endometriosis. We have also determined the effect of SIP on MMP-3 regulation relative to estradiol (E), progesterone (P) and interleukin-1α (IL-1α), an inflammatory cytokine associated with MMP expression and endometriosis. Design: Endometrial stromal cells were isolated from proliferative phase (days 10–12) biopsies from normal women with no history of endometriosis or uterine dysfunction. Cells were isolated by established methods and maintained in monolayers on Type-1 collagen in DMEM/F-12 media with 3% serum, steroids, IL-1α or SIP. Materials/Methods: SIP has homology with p205, a protein isolated from human synovial fluid. Using anti-p205 antibody coupled sepharose beads and an immunoaffinity column, SIP was extracted from human follicular fluid from women without endometriosis. Following elution from the column, the p205 bound fraction was found to contain SIP activity and gave a single band at 48 kD after SDS-PAGE. Isolated stromal cells were maintained in vitro in the presence of E (1 nM) or E plus P (E = 1 nM, P = 500 nM) for 0-96 hours prior to 24 hr exposure to IL-1α (100 pg/mL) or SIP (50 μg/mL). Conditioned media were analyzed for MMP-3 protein by established Western procedures. Results: Treatment of isolated endometrial stromal cells with E is associated with MMP-3 expression while treatment with E and P suppressed MMP-3. Simultaneous addition of SIP to either steroid treatment resulted in a significant stimulation of MMP-3 expression. Pretreatment of stromal cells with the combination of E and P prevented induction of MMP-3 by IL-1α, but a similar pretreatment of cells with E and P was unable to prevent MMP-3 stimulation by SIP. Conclusions: These results indicate that SIP, a follicular fluid protein, can stimulate the expression of endometrial MMP-3 and, unlike IL-1α, the stimulatory effects of SIP are not blocked by prior P exposure. Since endometrial MMP expression has been implicated in the development of endometriosis, the introduction of SIP into the peritoneal fluid at ovulation could contribute to a local environment which enhances establishment and/or progression of endometriosis. Supported By: Supported through cooperative agreement (U54-HD-37321) as part of the Specialized Cooperative Centers Program in Reproduction Research and by a grant from the Endometriosis Association.