Bcl-2 interacting protein 3 (BNIP3) promotes tumor growth in breast cancer under hypoxic conditions through an autophagy-dependent pathway

Hypoxia-induced autophagy has been implicated in many cancers. Bcl-2 interacting protein 3 (BNIP3) has been associated with hypoxia, whose aberrant expression is involved in the carcinogenesis of breast cancer (BC). Here, we aim to investigate the role of hypoxia-induced autophagy and the mechanistic actions of the bioinformatically identified BNIP3 in BC. The expression pattern of BNIP3 in BC tissues and cell lines was examined using RT-qPCR and Western blot analyses. The binding affinity among BNIP3, BECN1 and BCL-2 was characterized by co-immunoprecipitation. BNIP3 expression was manipulated to assess its effects on BC cell malignant phenotypes, evaluated by cell counting kit-8, Transwell and wound healing assays, and on BC autophagy under hypoxic conditions. A BC tumor xenografts mouse model was further established to substantiate <i>in vitro</i> findings. Up-regulated expression of BNIP3 was found in BC tissues and cell lines, and BNIP3 expression was positively correlated with hypoxia exposure duration. BNIP3 knockdown restricted BC cell proliferation, invasion, and migration under hypoxic conditions. BNIP3 activated BC cell autophagy by inhibiting the binding between BCL-2 and BECN1 under hypoxic conditions. BNIP3-induced autophagy activation enhanced malignant phenotypes of BC cells, thus accelerating the tumorigenesis of BC cells <i>in vivo</i>. These data collectively supported the tumor-promoting role of BNIP3 in autophagy activation of BC under hypoxic conditions, highlighting a potential therapeutic target against BC.

缺氧诱导自噬已被证实与多种癌症密切相关。Bcl-2相互作用蛋白3（Bcl-2 interacting protein 3, BNIP3）与缺氧状态存在关联，其异常表达参与了乳腺癌（Breast Cancer, BC）的癌变过程。本研究旨在探讨缺氧诱导自噬的作用，以及经生物信息学筛选鉴定得到的BNIP3在乳腺癌中的作用机制。本研究通过实时定量聚合酶链反应（RT-qPCR）和蛋白质印迹（Western blot）分析，检测了BNIP3在乳腺癌组织及细胞系中的表达模式。通过免疫共沉淀（co-immunoprecipitation）实验，验证了BNIP3、BECN1与BCL-2三者之间的结合亲和力。通过调控BNIP3的表达水平，利用细胞计数试剂盒-8（CCK-8）、Transwell及划痕愈合实验，评估其对乳腺癌细胞恶性表型的影响，并检测其对缺氧条件下乳腺癌细胞自噬的调控作用。本研究进一步构建了乳腺癌异种移植瘤小鼠模型，以验证体外实验结果。研究发现，BNIP3在乳腺癌组织及细胞系中呈高表达状态，且其表达水平与缺氧暴露时长呈正相关。在缺氧条件下，敲低BNIP3的表达可抑制乳腺癌细胞的增殖、侵袭与迁移能力。缺氧条件下，BNIP3可通过抑制BCL-2与BECN1的结合，激活乳腺癌细胞的自噬过程。BNIP3介导的自噬激活可增强乳腺癌细胞的恶性表型，进而在体内促进乳腺癌细胞的成瘤能力。上述实验结果共同证实，在缺氧条件下BNIP3通过激活自噬发挥促癌作用，为乳腺癌治疗提供了潜在的分子靶点。