Soluble endoglin antagonizes Met signaling in spindle carcinoma cells

Abstract

Increased levels of soluble endoglin (Sol-Eng) correlate with poor outcome in human cancer. We have previously shown that shedding of membrane endoglin, and concomitant release of Sol-Eng is a late event in chemical mouse skin carcinogenesis associated with the development of undifferentiated spindle cell carcinomas (SpCCs). In this report, we show that mouse skin SpCCs exhibit a high expression of hepatocyte growth factor (HGF) and an elevated ratio of its active tyrosine kinase receptor Met versus total Met levels. We have evaluated the effect of Sol-Eng in spindle carcinoma cells by transfection of a cDNA encoding most of the endoglin ectodomain or by using purified recombinant Sol-Eng. We found that Sol-Eng inhibited both mitogen-activated protein kinase (MAPK) activity and cell growth in vitro and in vivo. Sol-Eng also blocked MAPK activation by transforming growth factor-β1 (TGF-β1) and impaired both basal and HGF-induced activation of Met and downstream MAPK. Moreover, Sol-Eng strongly reduced basal and HGF-stimulated spindle cell migration and invasion. Both Sol-Eng and full-length endoglin were shown to interact with Met by coimmunoprecipitation experiments. However, full-length endoglin expressed at the plasma membrane of spindle carcinoma cells had no effect on Met signaling activity, and was unable to inhibit HGF-induced cell migration/invasion. These results point to a paradoxical suppressor role for Sol-Eng in carcinogenesis.

Endoglin: Beyond the Endothelium

“…High levels of sol-eng have been measured in the circulation of women developing preeclampsia-a disease characterized by a high blood pressure and vascular abnormalities during pregnancy [27]. In cancer, different studies have reported conflicting data about the levels of sol-eng [28][29][30]. The anti-angiogenic function described for sol-eng suggests that it has a tumor-suppressor role in cancer, which is in contrast to studies reporting that high levels of sol-eng correlate to poor patient prognosis [29].…”

A suppressor role for soluble endoglin in cancer

“…A characteristic of skin spindle carcinomas shared by other types of advanced tumors, including basal breast carcinomas, is the secretion of high levels of hepatocyte growth factor (HGF) and hyperactivation of Met, its tyrosine kinase receptor. Of note, Sol-Eng strongly inhibited both basal and HGF-induced Met activation and downstream MAPK signaling activity as well as basal and HGF-stimulated carcinoma cell migration and invasion [47] . The mechanism for this action is unclear and may involve the binding of Sol-Eng to Met on the cell surface, preventing its HGF-mediated activation and dimerization, but promoting its internalization and degradation independently of HGF.…”

“…In a recent article, we explored whether Sol-Eng affects the malignant properties of highly aggressive skin spindle carcinoma cells [47] . We found that Sol-Eng inhibits carcinoma cell proliferation, as wells as basal and TGF-β1-stimulated mitogen-activated protein kinase (MAPK) signaling activity.…”

“…The mechanism for this action is unclear and may involve the binding of Sol-Eng to Met on the cell surface, preventing its HGF-mediated activation and dimerization, but promoting its internalization and degradation independently of HGF. Interestingly, full-length membrane endoglin also binds Met, as shown by coimmunoprecipitation experiments, but it is unable to influence Met stability and signaling activity [47] . Recent studies indicate that the binding of Sol-Eng to Met is not direct (our unpublished results) and might be mediated by some of the proteins that associate with Met in a multiprotein complex at the plasma membrane, such as plexins, the hyaluronan receptor CD44 or integrins [48] .…”

Reduced expression of the murine HLA-G homolog Qa-2 is associated with malignancy, epithelial-mesenchymal transition and stemness in breast cancer cells

“…For Western blot analysis, cells were lysed in RIPA buffer containing a cocktail of protease and phosphatase inhibitors, as described 39 . For immunodetection of proteins, the following primary antibodies (Abs) were used: mAb ECCD for E-cadherin (dilution 1:250), kindly provided by Dr A. Cano (Instituto de Investigaciones Biomédicas Alberto Sols, Spain), mAbs 610153 (1:2000) and RV202 (1:250) for β-catenin and vimentin, respectively, from BD Biosciences; mAb EPR1600Y (1:1500) for CK5 from Abcam; mAb 327 (1:500) for Src was a kind gift of Dr. J.S.…”