Smoothened as a new therapeutic target for human osteosarcoma

<p>Abstract</p> <p>Background</p> <p>The Hedgehog signaling pathway functions as an organizer in embryonic development. Recent studies have demonstrated constitutive activation of Hedgehog pathway in various types of malignancies. However, it remains unclear how Hedgehog pathway is involved in the pathogenesis of osteosarcoma. To explore the involvement of aberrant Hedgehog pathway in the pathogenesis of osteosarcoma, we investigated the expression and activation of Hedgehog pathway in osteosarcoma and examined the effect of SMOOTHENED (SMO) inhibition.</p> <p>Results</p> <p>To evaluate the expression of genes of Hedgehog pathway, we performed real-time PCR and immunohistochemistry using osteosarcoma cell lines and osteosarcoma biopsy specimens. To evaluate the effect of SMO inhibition, we did cell viability, colony formation, cell cycle <it>in vitro </it>and xenograft model <it>in vivo</it>. Real-time PCR revealed that osteosarcoma cell lines over-expressed <it>Sonic hedgehog</it>, <it>Indian hedgehog</it>, <it>PTCH1</it>, <it>SMO</it>, and <it>GLI</it>. Real-time PCR revealed over-expression of <it>SMO, PTCH1</it>, and <it>GLI2 </it>in osteosarcoma biopsy specimens. These findings showed that Hedgehog pathway is activated in osteosarcomas. Inhibition of SMO by cyclopamine, a specific inhibitor of SMO, slowed the growth of osteosarcoma in vitro. Cell cycle analysis revealed that cyclopamine promoted G1 arrest. Cyclopamine reduced the expression of accelerators of the cell cycle including cyclin D1, cyclin E1, SKP2, and pRb. On the other hand, p21^cip1wprotein was up-regulated by cyclopamine treatment. In addition, knockdown of <it>SMO </it>by <it>SMO </it>shRNA prevents osteosarcoma growth in vitro and in vivo.</p> <p>Conclusions</p> <p>These findings suggest that inactivation of SMO may be a useful approach to the treatment of patients with osteosarcoma.</p

Suppression of Osteosarcoma Cell Invasion by Chemotherapy Is Mediated by Urokinase Plasminogen Activator Activity via Up-Regulation of EGR1

Background: The cellular and molecular mechanisms of tumour response following chemotherapy are largely unknown. We found that low dose anti-tumour agents up-regulate early growth response 1 (EGR1) expression. EGR1 is a member of the immediate-early gene group of transcription factors which modulate transcription of multiple genes involved in cell proliferation, differentiation, and development. It has been reported that EGR1 act as either tumour promoting factor or suppressor. We therefore examined the expression and function of EGR1 in osteosarcoma. Methods: We investigated the expression of EGR1 in human osteosarcoma cell lines and biopsy specimens. We next examined the expression of EGR1 following anti-tumour agents treatment. To examine the function of EGR1 in osteosarcoma, we assessed the tumour growth and invasion in vitro and in vivo. Results: Real-time PCR revealed that EGR1 was down-regulated both in osteosarcoma cell lines and osteosarcoma patients’ biopsy specimens. In addition, EGR1 was up-regulated both in osteosarcoma patient’ specimens and osteosarcoma cell lines following anti-tumour agent treatment. Although forced expression of EGR1 did not prevent osteosarcoma growth, forced expression of EGR1 prevented osteosarcoma cell invasion in vitro. In addition, forced expression of EGR1 promoted downregulation of urokinase plasminogen activator, urokinase receptor, and urokinase plasminogen activity. Xenograft mice models showed that forced expression of EGR1 prevents osteosarcoma cell migration into blood vessels. Conclusions: These findings suggest that although chemotherapy could not prevent osteosarcoma growth in chemotherapy-resistant patients, it did prevent osteosarcoma cell invasion by down-regulation of urokinase plasminogen activity via up-regulation of EGR1 during chemotherapy periods

The knock-down of overexpressed EZH2 and BMI-1 does not prevent osteosarcoma growth

Polycomb group proteins control the transcriptional memory of cells by maintaining the stable silencing of specific sets of genes through chromatin modifications. Polycomb group protein complexes control gene repression through recruitment of histone deacetylase. This recruitment leads to trimethylation of Lys27 of histone H3 (H3K27). Histone H3K27 trimethylation is a property of stably silenced heterochromatin. EZH2 and BMI-1 are pivotal components of polycomb group protein complexes. Increased EZH2 levels have been found in several malignancies and reported as a molecular biomarker of poor prognosis. Similarly, BMI-1 has also been found to be associated with malignant transformation. In addition, inhibition of EZH2 or BMI-1 inhibits the growth of various types of malignancies. The expression of BMI-1 and EZH2 in human osteosarcoma has not been clearly determined. We examined the potential involvement of aberrant polycomb group protein expression in the pathogenesis of osteosarcoma. Real-time PCR revealed that expression of EZH2 in 143B, HOS, NOS-1 and Saos2 was increased compared to normal osteoblasts. BMI-1 was also up-regulated in 143B, HOS and NOS-1. Expression of EZH2 and BMI-1 were up-regulated in osteosarcoma patient biopsy specimens compared to normal bone. Immunohistochemical examinations showed that EZH2 and BMI-1 were up-regulated in osteosarcoma cells and that trimethylation of histone H3K27 was increased. We examined the effects of knock down of EZH2 and BMI-1 by shRNA. Unexpectedly, the knock-down of EZH2 and BMI-1 did not prevent osteosarcoma growth either in vitro or in vivo. Our findings suggest that EZH2 and BMI-1 may be tumorassociated antigens of osteosarcoma, but are not useful molecular targets of osteosarcoma treatment

Smoothened as a new therapeutic target for human osteosarcoma

Background: The Hedgehog signaling pathway functions as an organizer in embryonic development. Recent studies have demonstrated constitutive activation of Hedgehog pathway in various types of malignancies. However, it remains unclear how Hedgehog pathway is involved in the pathogenesis of osteosarcoma. To explore the involvement of aberrant Hedgehog pathway in the pathogenesis of osteosarcoma, we investigated the expression and activation of Hedgehog pathway in osteosarcoma and examined the effect of SMOOTHENED (SMO) inhibition. Results: To evaluate the expression of genes of Hedgehog pathway, we performed real-time PCR and immunohistochemistry using osteosarcoma cell lines and osteosarcoma biopsy specimens. To evaluate the effect of SMO inhibition, we did cell viability, colony formation, cell cycle in vitro and xenograft model in vivo. Real-time PCR revealed that osteosarcoma cell lines over-expressed Sonic hedgehog, Indian hedgehog, PTCH1, SMO, and GLI. Realtime PCR revealed over-expression of SMO, PTCH1, and GLI2 in osteosarcoma biopsy specimens. These findings showed that Hedgehog pathway is activated in osteosarcomas. Inhibition of SMO by cyclopamine, a specific inhibitor of SMO, slowed the growth of osteosarcoma in vitro. Cell cycle analysis revealed that cyclopamine promoted G1 arrest. Cyclopamine reduced the expression of accelerators of the cell cycle including cyclin D1, cyclin E1, SKP2, and pRb. On the other hand, p21cip1 wprotein was up-regulated by cyclopamine treatment. In addition, knockdown of SMO by SMO shRNA prevents osteosarcoma growth in vitro and in vivo. Conclusions: These findings suggest that inactivation of SMO may be a useful approach to the treatment of patients with osteosarcoma