Abstract 4140: Role of nitric oxide in invasiveness of tumor cells irradiated with carbon-ion beams
Authors: Fujita Mayumi , Imadome Kaori , Shoji Yoshimi , Cheng Robert , Kesarwala Aparna H. , Wink David A. , Imai Takashi 
Published: August 2015

We previously reported that carbon-ion (C-ion) irradiation suppresses the invasiveness of several pancreatic cancer cell lines such as MIAPaCa-2, BxPC-3, and AsPC-1; however, we also observed that C-ion irradiation enhanced PANC-1 invasion. Most invading PANC-1 cells were nitric oxide (NO)-producing cells; the NOS-NO-PI3K-AKT pathway was activated in these cells. In addition, the actin-binding AKT substrate, Girdin, which modulates the actin organization and has important role in AKT-dependent cell motility, was activated and co-localized with p-AKT at the lamellipodia. C-ion irradiation increased the NO-producing cell population, thereby enhancing C-ion irradiation-enhanced PANC-1 invasion. In contrast to PANC-1 cells, NO levels as well as the number of NO-producing cells were decreased in C-ion irradiated MIAPaCa-2, indicated that the NO reduction might cause the suppression of MIAPaCa-2 invasion. The aim of this study is to clarify the role of NO in altered invasiveness of C-ion irradiated tumor cells. Treatment of PANC-1 with NO donor, DETA/NO, enhanced PANC-1 invasion. Interestingly, DETA/NO also increased MIAPaCa-2 invasion, indicated that NO contributes to the enhancement of MIAPaCa-2 invasiveness. The reduced invasiveness of C-ion irradiated MIAPaCa-2 was slightly but significantly recovered by the treatment with DETA/NO, but the recovered levels were still much less than the invasiveness of non-irradiated MIAPaCa-2. Thus, the reduction of NO levels involves in the decreased invasiveness of C-ion irradiated MIAPaCa-2, but there are additional factor regulating the invasiveness of cells irradiated with C-ion beams. Indeed, C-ion irradiation reduced GTP-Rac1 and GTP-RhoA expression, the active form of Rac1 and RhoA, which are known as two master regulators of cell motility. The reduction of GTP-Rac1 or GTP-RhoA was recovered by the treatment of proteasome inhibitor, indicated that those proteins were undergo degradation via the ubiquitin-proteasome pathway. So far, IAPs, Inhibitors of Apoptosis Proteins, and HACE1, HECT-domain containing E3 ubiquitin-ligase, were reported as direct E3 ubiquitin ligase of Rac1. Of those, XIAP was selectively induced and was co-precipitated with GTP-Rac1 in C-ion irradiated MIAPaCa-2. In conclusion, NO has a significant role in enhancing invasive potential of both PANC-1 and MIAPaCa-2 cells. The alteration of NO levels upon C-ion irradiation modulates the invasiveness of irradiated cells. Also, reductions of GTP-Rac1 and GTP-RhoA have the additional effects on the C-ion reduced MIAPaCa-2 invasion. Several studies have reported that NO modulates ubiquitin-proteasomal degradation of proteins. The effect of NO on the GTP-Rac1 and GTP-RhoA degradation remain unknown, and further researches are needed to clarify whether the NO reduction affects to the GTP-Rac1 or GTP-RhoA degradation observed in C-ion irradiated MIAPaCa-2.

Citation Format: Mayumi Fujita, Kaori Imadome, Yoshimi Shoji, Robert Cheng, Aparna H. Kesarwala, David A. Wink, Takashi Imai. Role of nitric oxide in invasiveness of tumor cells irradiated with carbon-ion beams. [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 4140. doi:10.1158/1538-7445.AM2015-4140