Nuclear localization of LDL receptor-related protein 1B in mammary gland carcinogenesis

LRP1B intracellular domain is released and transported to the nucleus; however, pathological consequences of this nuclear transport are largely unclear. We aimed to unravel the pathobiological significance of nuclear localization of LRP1B intracellular domain in mammary gland carcinogenesis. Immunohistochemical staining using antibodies for LRP1B intracellular domain was performed to determine LRP1B expression in 92 invasive ductal breast carcinomas. LRP1B immunoreactivity was detected in the surface membrane and cytoplasm of 60 of 92 invasive ductal carcinomas and in the nucleus of 15 of 92 carcinomas. Nuclear LRP1B was significantly associated with poor patient prognosis, particularly luminal A type breast cancer, where it was significantly related to nodal metastasis. Doxycycline-dependent nuclear expression of LRP1B intracellular domain was established in cultured breast cancer cells. Enforced nuclear expression significantly increased Matrigel invasion activity in MCF-7 and T47D luminal A breast cancer cells. Moreover, enforced nuclear expression of LRP1B intracellular domain facilitated MCF-7 cells growth in mammary fat pad of nude mice, which was supplemented with estrogen. Comprehensive microarray-based analysis demonstrated that nuclear expression of LRP1B intracellular domain significantly increased long non-coding RNA nuclear paraspeckle assembly transcript 1 (NEAT1) expression, which facilitates breast cancer invasion with poor prognosis. Nuclear-localized LRP1B intracellular domain promoted breast cancer progression with poor prognosis, possibly through the NEAT1 pathway. Nuclear transport of LRP1B intracellular domain could be a therapeutic target for breast cancer patients. KEY MESSAGES: Nuclear LRP1B was significantly associated with poor patient prognosis. Nuclear LRP1B increased Matrigel invasion activity of breast cancer cells. Nuclear expression of LRP1B intracellular domain increased NEAT1 expression.