Altered expression of a cell-cycle suppressor gene, Tob-1, in endometriotic cells by cDNA array analyses

Objective: Interleukin (IL)-1β, a product of activated peritoneal macrophages, is a central cytokine coordinating neovascularization and monocyte chemotaxis in endometriotic implants. To evaluate the effects of this cytokine on normal endometrial stromal cells and endometriotic stromal cells we performed cDNA expression array analyses before and after exposure to IL-1β. Design: Nested case-control study of women with and without laparoscopic evidence of endometriosis. Setting: Reproductive endocrinology clinic at a university hospital. Patient(s): Endometriosis and normal endometrial biopsies from eight patients were used to prepare stromal cell cultures from which mRNA was extracted. Intervention(s): None. Main Outcome Measure(s): Commercially available expression arrays (Atlas Human cDNA Expression Array, Clontech, representing 597 individual genes) were used to screen for mRNAs whose expression was affected by 12 hours of exposure to IL-1β (10 ng/mL). Northern blotting and subsequent quantitative densitometric evaluation was done to confirm steady-state levels of Tob-1 mRNA transcripts. Result(s): Array analyses revealed a cell-cycle regulatory gene, Tob-1, which was differentially expressed by the two cell types after incubation with IL-1β. Tob-1 was reduced 48% in endometriotic stromal cells exposed to IL-1β, but there was only a 16% reduction in normal endometrial stromal cells. Replicate Northern analyses (n = 4) showed that exposure to IL-1β for 12 hours resulted in a 25% ± 5% diminution of Tob-1 mRNA in endometriotic stromal cells. In contrast, no significant decrease (<3%) was observed in IL-1β exposed normal endometrial stromal cells. Conclusion(s): Tob-1, a cell-cycle inhibitor gene is differentially responsive to IL-1β in endometriotic stromal cells compared to normal endometrial stromal cells. IL-1β down-regulated Tob-1 in endometriotic stromal cells, but had no significant effect on normal endometrial stromal cells. Our results suggest that IL-1β promotes growth of endometriotic lesions through inhibition of Tob-1. These findings are the first to associate IL-1β with an alteration of cell-cycle gene expression in cells derived from endometriotic implants.