Abstract 5080: HIF-1 is responsible for the induction of cancer-associated fibroblasts in hypoxic tumor microenvironment

Abstract

Abstract In tumor tissues, tumor cells and tumor stromal cells interact with each other, generating the complex tumor microenvironment (TME). Whereas cancer-associated fibroblasts (CAFs) are dominant cells among tumor stromal cell types, the induction of CAFs in TME still remains unclear. Given that TME turns to be hypoxic while tumor is growing, we hypothesized that hypoxia in TME would contribute to induction of CAFs. In this study, we focused on a role of hypoxia-inducible factor-1 (HIF-1), a key transcription factor in hypoxic responses, and examined the implication of HIF-1 in the induction of CAFs in TME. The mouse lymphoma cell line, E.G7 cells, which had been transfected with HIF-1α shRNA (E.G7- HIF-1α shRNA) were cultured under hypoxia with an O2 concentration of 1.0%. As controls, E.G7 cells or those which had been transfected with control shRNA (E.G7-control shRNA) were also cultured under the same hypoxic condition as in case of E.G7- HIF-1α shRNA. Three days later, the culture medium was harvested for following experiments. To evaluate a role of HIF-1α in migration of CAFs progenitor cells into TME, mouse bone marrow cells as CAFs progenitor cells were put in the upper compartment, and hypoxic culture medium was added in the lower compartment of a transwell chamber. We observed that the number of α-smooth muscle actin (α-SMA)-positive cells that had migrated was decreased when hypoxic culture medium from E.G7- HIF-1α shRNA was added in the lower compartment. Transforming growth factor-beta (TGF-β) has been reported to be one of soluble factors which are responsible for induction of CAFs. Thus, we examined the level of TGF-β in hypoxic culture medium by ELISA, demonstrating that it was decreased in the medium from E.G7- HIF-1α shRNA as compared with E.G7-control shRNA or E.G7 cells. Next, we examined the association between HIF-1α inhibition and CAFs induction in a tumor-bearing mouse model. C57BL/6 mice were subcutaneously administered E.G7-HIF-1α shRNA, E.G7-control shRNA, or E.G7 cells at the flank. Three weeks later, tumor tissues were harvested from the mice, and α-SMA-positive cells in tumor tissues were examined by immunohistochemistry. The data showed that α-SMA-positive CAFs were decreased in E.G7-HIF-1α shRNA tumor tissues as compared with E.G7-control shRNA, or E.G7 tumor tissues. In addition, tumor growth was significantly suppressed in mice bearing E.G7-HIF-1α shRNA, while inhibition of HIF-1α did not exert a suppressive effect on the proliferation of E.G7 cells in vitro. These data indicated that HIF-1α would play a critical role in the induction of CAFs via TGF-β in hypoxic TME. Inhibition of HIF-1α could have contributed to reduction of CAFs in tumor tissues, leading to suppression of tumor growth. These results provide a novel rationale with TME-targeted strategy against cancer. Citation Format: Koji Teramoto, Yoko Kataoka, Tomoyuki Igarashi, Yasuhiko Ohshio, Jun Hanaoka, Yataro Daigo. HIF-1 is responsible for the induction of cancer-associated fibroblasts in hypoxic tumor microenvironment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5080. doi:10.1158/1538-7445.AM2015-5080