Y-Box BIinding Protein-1 (YB-1): A Major Contributor to Sarcoma Cell Motility and Aggressiveness

Objective: To identify the potential roles played by of YB-1 in childhood sarcomas, notably, metastatic spread and resistance to therapies. Aims: Aim (1): Identify the effect of YB-1 knockdown on the migration and invasion of childhood sarcoma cell lines. Aim (2): Detecting the potential relationship between YB-1 and hypoxia inducible factor 1 alpha (HIF1α). Background: Sarcomas are a diverse group of malignant neoplasms of which are characterized by early metastatic spread, aggressive behavior, and poor prognosis. One of the genes believed to play a role in sarcomatogenesis is the Y-box binding protein-1 (YB-1). YB-1 is a member of the highly conserved heat shock domain- containing family of proteins known to bind single and double stranded DNA and single stranded RNA, thereby controlling transcription and translation of a multitude of genes. Our group recently demonstrated that increased expression of YB-1 in breast cancer cells initiated an epithelial-mesenchymal transition (EMT), led to increased migration, and resulted in a metastatic phenotype of breast cancer cells. Studies that comprehensively investigate the role of YB-1 in sarcoma development are currently lacking. Hypothesis: Elevated YB-1 levels, observed in childhood sarcomas, promote the migration and invasion of sarcoma cells and contribute to their aggressive phenotype. More specifically, YB-1 alters activity of the downstream effector hypoxia-inducible factor 1α (HIF1α) to promote the metastatic phenotype. Research Methodology: Aim (1): MG63, MNNG (osteosarcoma), TC32 (Ewing family tumor), and Rh30 (Rhabdomyosarcoma) cell lines were chosen as models for the current study. The motility of control siRNA vs YB-1 targeting siRNA mediated knockdown cells were assessed by in vitro and in vivo studies. Aim (2): Hypoxia chamber incubations, immunoblotting, RNA polysomal fractionation and real-time qRT-PCR were used to study the relationship between YB-1 and HIF1α expression in sarcoma cell lines. Results: Blcoking YB-1 expression led to a significant reduction in cell motility (migration/invasion). We also found that under hypoxic conditions, both YB-1 and HIF1α were induced. Using RNA polysomal fractionation and qPCR, we determined that YB-1 is a major translational regulator of HIF1α. These findings provide a mechanism to explain how YB-1 promotes sarcoma cell metastasis. Conclusions: 1) YB-1 strongly promotes the migration and invasion of sarcoma cells. 2) YB-1 is a major translational regulator of HIF1α. 3- YB-1 is likely contributing to the aggressive nature of sarcoma cells and may represent a promising novel therapeutic target for treatment of sarcomas. Relevance: Dissemination of malignant sarcoma cells and resistance to therapies are the major challenges facing clinicians treating sarcoma patients. Therefore identifying the proteins responsible for this phenotype may result in novel therapies for the treatment of sarcomas.