ALAD通过调控NF-κB信号通路抑制乳腺癌发展的机制研究

δ-aminolevulinic acid dehydratase (ALAD), the most imporatnat blood lead transporter protein, is a necessary enzyme for porphyrin and heme synthesis. However, the role of ALAD in tumorigenesis and progression is still unknown. Our previous study showed that ALAD is down-regulated in breast cancer tissues and reduced ALAD expression predicts poor outcome in patients with breast cancer. Functional study showed that ALAD inhibits breast cancer cell proliferation and invasion, and promotes cell apopotosis. The ubiguitin-proteasome pathway is an.important pathway for the intracellular proteins target degradation and aberration in proteasome is closely related to the tumor development and progression. Our previous study indicated that ALAD could bind to the proteasom and suppress the activity of NF-κB critical factor p50/p65 and also inhibit the TNF-α-induced IκB degradation. In addition, we observed that the ALAD expression is regulated by the methylation of its promoter. In this study, we aim to demostrate that ALAD is hypmethylated in breast cancer, leading to a decreased ALAD expresion level, resulting in the over activation of proteasome and the NF-κB signaling to promote breast cancer development and progression.

δ-氨基乙酰丙酸脱水酶（ALAD）是卟啉及血红素合成过程中必要的酶之一，并且是已知的最主要的血铅转运蛋白。但ALAD在肿瘤发生发展中作用尚无报道。课题组前期研究发现，ALAD在乳腺癌组织中表达下调，且ALAD低表达与患者不良预后相关。功能学实验表明ALAD抑制乳腺癌增殖和侵袭能力，促进细胞凋亡。泛素-蛋白酶体途径是细胞内蛋白质选择性降解的重要途径，蛋白酶体的异常与恶性肿瘤的发生发展密切相关。课题组前期研究发现ALAD能与蛋白酶体结合，抑制NF-κB信号通路关键因子p50/p65激活，且能抑制肿瘤坏死因子α所诱导的IκB的降解，同时ALAD表达受其启动子甲基化水平调控。本研究将证实，ALAD启动子在乳腺癌组织中呈高甲基化，导致ALAD表达下调，使蛋白酶体过度活化，NF-κB信号通路过度激活，最终促进乳腺癌发生发展。

ALAD是卟啉及血红素合成过程中必要的酶之一，并且是已知的最主要的血铅转运蛋白。但ALAD在肿瘤发生发展中作用尚无报道。课题研究发现，ALAD在乳腺癌组织中表达下调，且ALAD低表达与患者不良预后相关。体外体内功能学实验表明ALAD抑制乳腺癌肿瘤生长和转移。进一步研究发现ALAD通过抑制p50/p65激活，降低NF-κB信号通路的活性，且ALAD表达受其启动子甲基化水平调控。同时，ALAD是miR-183-5p的下游靶基因，miR-183-5p可通过降低ALAD表达促进乳腺癌促进乳腺癌转移。LINC00665作为ALAD下游调控的靶基因，可通过ceRNA机制调控miR-379-5p促进乳腺癌进展。但ALAD调控LINC00665的分子机制还有待进一步阐明。