Abstract 930: Role of DLK1 in sarcoma stem cells

Abstract

Abstract Sarcoma is a rare form of cancer that comprises about 1% of all malignancies. A large proportion of deaths by sarcomas are caused by tumor metastasis, of which the biological basis remains obscure. A significant body of evidence suggests that only a small population of sarcoma cells possess the ability to initiate and maintain tumors. These tumor-initiating cells have the ability to self-renew, recapitulating the cellular heterogeneity of the original cancer, and thus are often referred as cancer stem like cells (CSLCs).Delta-like factor 1 (DLK1) was cloned in the preadipocyte cells 3T3-L1 cDNA library. Previous studies reported on the role of DLK1 in mesenchymal stem cell differentiation, adipogenesis, myogenesis, and osteoblastogenesis. It was reported that DLK1+ liver cancer cells have characteristics similar to those of CSLCs and that DLK1 could be a potential therapeutic target against the liver CSLCs. However, little is known about role of DLK1 in CSLCs of sarcoma. The mRNA (real time PCR) and protein (Western blot) expression of DLK1 from 13 sarcoma cell lines was examined. CSLCs from sarcoma cell lines were isolated using FACS with CD133 and sphere forming assay. The effect of DLK1 on sarcoma tumorigenesis was examined using cell proliferation and cell invasion assays by DLK1 siRNA treatment.Real-time PCR showed the increased expression of DLK1 mRNA in sarcoma cell lines. In particular, DLK1 mRNA was highly expressed in U2OS (osteosarcoma), SW872 (liposarcoma), A204 (rhabdomyosarcoma), and HS-SYII (synovial sarcoma) cells. We observed a reduction in cell proliferation and invasion in U2OS, A204, and sw872 cells treated with DLK1 siRNA. CSLCs were isolated from U2OS, A204, and sw872 by the FACS sorting method using the CD133, a CSLC marker in sarcoma. The number of active sarcoshperes in CD 133+ cells were significantly higher than that in CD133- cells by sphere forming assay. Soft agar assays revealed the presence of many more colonies in CD133+ cells than in CD133- or wild type cells. To investigate the effect of DLK1 on sarcoma CSLCs, sw872 cells were categorized into four groups: wild type, CD133-, CD133+ and spheres. Real-time PCR and western blot were used to detect the DLK1 gene in all four groups. We observed that DLK1 expression in sw872 CSLCs (CD133+ and spheres) were relatively low. We found that suppression of DLK1 by siRNA inhibited the invasiveness of CSLCs although it inhibited more effectively to activation of invasive cells as well as cell proliferation in sw872 non-CSLCs.These results suggest that DLK1 may play a role in tumorigenesis of CSLCs and cancer cells in various sarcomas. Citation Format: Ilkyu Han, Sun Hee Ahn, Han-Soo Kim. Role of DLK1 in sarcoma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 930. doi:10.1158/1538-7445.AM2017-930