The HtrA family of serine proteases takes part in cellular stress response including heat shock, inflammation and cancer. Downregulation of human HtrA1 and HtrA3 genes has been reported in some cancers, including endometrial cancer (EC), suggesting a tumor-suppressor role for both genes. The mechanism of the HtrA function is not known, however, evidence exists showing that both HtrA1 and HtrA3 regulate biological processes by modulating TGF-β signaling. In the presented study the expression of human HtrA1, HtrA2, HtrA3 and TGF-β1 genes was examined in 124 endometrial tissue specimens including 88 cancers and 36 normal endometria. The expression of the tested genes was evaluated at mRNA and protein levels by semi-quantitative RT-PCR and western blotting methods, respectively. Our results showed significant decrease of HtrA1 and HtrA3 mRNA and protein levels in EC compared to normal tissues. The most dramatic decrease was found for HtrA3 at both mRNA and protein levels (3.2- and 5.6-fold, respectively). Moreover, the HtrA3 protein (short isoform) was not detected in 19% of the cancers, and its level decreased from the premenopausal to the postmenopausal group. The HtrA2 protein levels were significantly lower in EC tissues compared to normal tissues. We also found a significant increase of the TGF-β1 protein level in EC as well as a significant negative correlation between HtrA1/2/3 and TGF-β1 relative protein levels. Our results showing downregulation of HtrA1 and HtrA3 gene expression support previous studies suggesting a tumor suppressor role for these genes. Furthermore, our data suggest that HtrA2 may be involved in EC development as well as suggest the involvement of HtrA1, HtrA2 and HtrA3 in the inhibition of TGF-β signaling in endometrial tissues.

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