Abstract 3530: KITENIN works as a fine regulator of ErbB4 expression in colorectal cancer tissues in addition to E3-ubiquitin ligase Nrdp1
Authors: Bae Jeong A , Sun Eun Gene , Ko Yoo-Seung , Choi Hui Jeong , Jung Chaeyong , Lee Kyung-Hwa , Chung Ik Joo , Moon Kyung-Sub , Yu Young Hyun , Ha Hyung-Ho , Kim Hangun , Kim Kyung Keun 
Published: July 2017

Abstract
Purpose: Understanding the complex biological functions of E3-ubiquitin ligases may facilitate the modulation of E3-ubiquitin ligases as a promising approach for the development of novel anticancer drugs. We recently identified that the KITENIN/ErbB4-Dvl2-c-Jun axis works as a novel unconventional downstream signal of epidermal growth factor in colorectal cancer (CRC) tissues and that the immunohistochemical expression of KITENIN/ErbB4 was highly expressed in tumor tissues from advanced CRC stage. However, the detailed mechanisms that explain the higher levels of ErbB4 in colon cancer tissues are largely unknown. Here we investigated whether E3-ubiquitin ligases participate in the operation of the KITENIN/ErbB4-Dvl2-c-Jun axis and in the maintenance of elevated KITENIN/ErbB4 complex in CRC.
Results & Discussion: We found that Nrdp1, an E3-ligase for ErbB3/ErbB4, interacted with KITENIN (KAI1 C-terminal interacting tetraspanin) to form a functional KITENIN/ErbB4/Nrdp1 complex and is responsible for down-regulating Dvl2 within this complex. Interestingly, ErbB4 was resistant to degradation by Nrdp1 in KITENIN/Nrdp1-co-transfected CRC cells, and KITENIN bound to the C-terminal coiled-coil domain of Nrdp1. Chemical blockade of ErbB kinase did not block the action of EGF to increase in total/phospho-ErbB4 and phospho-ERK in KITENIN/ErbB4-cotransfected cells, whereas it blocked the action of EGF in ErbB4 alone-transfected CRC cells. In human CRC tissues, higher expressions of ErbB4 and KITENIN and lower expression of Dvl2 was observed in stage IV samples than in stage I, but a low level of Nrdp1 was expressed in both stages and it did not differ significantly by stage. These results indicated that Nrdp1 is necessary for the reduction in Dvl2 to generate c-Jun in the EGF-KITENIN/ErbB4-c-Jun axis, but more importantly, elevated KITENIN protects KITENIN-bound ErbB4 from Nrdp1-mediated degradation via physical collaboration between the KITENIN/ErbB4 complex and Nrdp1, but not via modulation of ErbB kinase activity. Thus, KITENIN functions in the maintenance of a higher expression level of ErbB4 in advanced CRC tissues, independent of ubiquitin-mediated degradation via Nrdp1.
Conclusion: Our present findings add a new component to our understanding of the molecular events underlying the regulation of ErbB4 expression level in CRC tissues: KITENIN is also a fine regulator of ErbB4 expression in addition to E3-ubiquitin ligase Nrdp1.
Citation Format: Jeong A Bae, Eun Gene Sun, Yoo-Seung Ko, Hui Jeong Choi, Chaeyong Jung, Kyung-Hwa Lee, Ik Joo Chung, Kyung-Sub Moon, Young Hyun Yu, Hyung-Ho Ha, Hangun Kim, Kyung Keun Kim. KITENIN works as a fine regulator of ErbB4 expression in colorectal cancer tissues in addition to E3-ubiquitin ligase Nrdp1 [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 3530. doi:10.1158/1538-7445.AM2017-3530