Role of Hedgehog Signaling in Malignant Pleural Mesothelioma

Abstract

Purpose: The aim of this study was to assess the activity of hedgehog signaling pathway in malignant pleural mesothelioma (MPM).Experimental Design: The expression of hedgehog signaling components was assessed by quantitative PCR and in situ hybridization in 45 clinical samples. Primary MPM cultures were developed in serum-free condition in 3% oxygen and were used to investigate the effects of smoothened (SMO) inhibitors or GLI1 silencing on cell growth and hedgehog signaling. In vivo effects of SMO antagonists were determined in an MPM xenograft growing in nude mice.Results: A significant increase in GLI1, sonic hedgehog, and human hedgehog interacting protein gene expression was observed in MPM tumors compared with nontumoral pleural tissue. SMO antagonists inhibited GLI1 expression and cell growth in sensitive primary cultures. This effect was mimicked by GLI1 silencing. Reduced survivin and YAP protein levels were also observed. Survivin protein levels were rescued by overexpression of GLI1 or constitutively active YAP1. Treatment of tumor-bearing mice with the SMO inhibitor HhAntag led to a significant inhibition of tumor growth in vivo accompanied by decreased Ki-67 and nuclear YAP immunostaining and a significant difference in selected gene expression profile in tumors.Conclusions: An aberrant hedgehog signaling is present in MPM, and inhibition of hedgehog signaling decreases tumor growth indicating potential new therapeutic approach.

Expression of Smoothened Protein in Colon Cancer and its Prognostic Value for Postoperative Liver Metastasis

“…Inhibition of SMO by cyclopamine, a specific inhibitor of SMO, slow the growth of osteosarcoma in vitro (Hirotsu et al, 2010). Treatment of malignant pleural mesothelioma-bearing mice with the SMO inhibitor HhAntag leads to a significant inhibition of tumor growth in vivo accompanied by decreased Ki-67 and nuclear YAP immunostaining (Shi et al, 2012). The expression of SMO mRNA is enhanced in the tumor nests of the nodular basal cell carcinoma (BCC), especially at the advancing portions, but is under the detectable level in the superficial BCC cases examined, indicating that smo mRNA expression might be associated with BCC tumor progression (Tojo et al,1999).…”

Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma

“…We previously observed that primary human MPM cells cultured in the physiologic condition [in own conditioned medium with growth factors (see Materials and Methods) and 3% O 2 ] could sustain stemness and DHH secretion (5). Therefore, we isolated primary cells from the orthotopic rat tumors and cultured them in this condition.…”

“…In MPM, increased SHH and GLI1 mRNA expression was detected in tumor tissues compared with normal mesothelium (5). High GLI1 expression (5) and high SMO and SHH protein levels (6) were associated with poor survival of MPM patients.…”

“…Recent findings of the activated Hedgehog (Hh) signaling pathway in MPM have underlined its role as a target for MPM treatment (5)(6)(7). The Hh pathway is one of the crucial stem cell signaling pathways that regulate embryonic development and adult tissue repair (8).…”

“…Nevertheless, mutations of Hh pathway components in MPM were reported to be relatively rare (17). So far, upregulation of the Hh signaling in MPM has been demonstrated in ligand-dependent autocrine manner, interestingly only mediated by DHH in the primary culture in 3% O 2 without serum (5). It is important to note that 2 of 6 MPM primary cells employed in that study were not responsive to a SMO antagonist (5) suggesting a possible role of paracrine activation in MPM.…”