Abstract PD1-04: Nuclear localization of intracellular domain of LDL receptor-related protein 1B predicts poor outcome in breast cancer; putative relation to NEAT1 mediated mammary gland carcinogenesis
Authors: Asano Y , Futamura M , Takeuchi T , Yoshida K 
Published: May 2019

Background:Low-density lipoprotein receptor-related protein 1B(LRP1B) is thought to have a pleiotropic biological function. Notably, intracellular domain of LRP1B is released and transported to nucleus in a γ-secretase dependent fashion; however, pathological property, which is driven by nuclear transport of intracellular domain of LRP1B is largely unclear. In this study, we aimed to unravel the pathological significance of nuclear localization of intracellular domain of LRP1B in mammary gland carcinogenesis. Aims: We examine the clinical significance of LRP1B for breast cancer and we clarify mechanism of nuclear localization of LRP1B in invasive ductal carcinoma. Methods: Immunohistochemical staining using newly generated antibodies to intracellular domain of LRP1B was used to determine LRP1B expression in 92 invasive ductal carcinomas of the breast. The clinicopathological significance including prognosis value was statistically analyzed. Doxycycline dependent nuclear expression of intracellular domain of LAP1B was established in cultured breast cancer cells. Subsequently, a series of in vitro experiments were performed to explore the role of nuclear localized intracellular domain of LRP1B in cultured breast cancer cells. Comprehensive microarray-based analysis followed by quantitative RT-PCR and chromatin immunoprecipitation assay was performed to know the altered molecular signature induced by nuclear localized intracellular domain of LRP1B. Results: Non-tumorous mammary duct epithelial cells did not exhibit LRP1B staining, whereas different degrees of LRP1B immunoreactivity were observed in 75 of 92 invasive ductal carcinoma of the breast. LRP1B immunoreactivity was found in surface membrane and cytoplasm of 60 of 92(65.2%) invasive ductal carcinoma cells, whereas it was detected in nucleus of 15 of 92(16.3%)cancer cells. Interestingly, nuclear LRP1B immunoreactivity was significantly associated with poor prognosis of the patients, especially with luminal A type breast cancers. Notably, nuclear localized intracellular domain of LRP1B significantly related to status of nodal metastasis in luminal A type breast cancers. Enforced nuclear expression significantly increased Matrigel invasion activity in MCF-7 luminal A breast cancer cells without affecting cell growth. Notably, nuclear expression of intracellular domain of LRP1B decreased transcription of LRP1B. Comprehensive microarray-based analysis demonstrated that nuclear expression of intracellular domain of LRP1B significantly increased the expression of long non-coding RNA nuclear paraspeckle assembly transcript1(NEAT1), which facilitates breast cancer invasion with poor survival. Conclusions: Present findings indicated that nuclear localized intracellular domain of LTP1B promoted breast cancer progression with a poor prognostic value, possible through NEAT1 pathway. Nuclear transport of intracellular domain of LRP1B could be a therapeutic target for breast cancer patients.

Citation Format: Asano Y, Futamura M, Takeuchi T, Yoshida K. Nuclear localization of intracellular domain of LDL receptor-related protein 1B predicts poor outcome in breast cancer; putative relation to NEAT1 mediated mammary gland carcinogenesis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD1-04.