Polarity protein Par6: Unraveling its mechanisms in tumor development and research advances

Partitioning-defective protein 6 (Par6), is a core regulator of cell polarity whose dysregulation is increasingly implicated in tumorigenesis and progression. This review aims to elucidate the molecular basis by which Par6 promotes tumor development in various cancer types. We first review the molecular structure of PAR6 and its general functions in normal cells, summarize the distinct expression patterns of Par6 isoforms (Pard6a, Pard6b, Pard6g) in different tumors and their divergent clinical implications. Subsequently, starting from the tumor biological functions of Par6, we elaborate in detail on the molecular interactions of PAR6 in tumor polarization and growth. In the TGF-β signaling pathway, phosphorylation of Par6 promotes RhoA degradation, thereby driving tumor cell epithelial-mesenchymal transition (EMT) and metastasis. Additionally, Par6 engages in crosstalk with multiple signaling pathways such as PI3K/Akt, MAPK/ERK, and Wnt, collectively coordinating the loss of cell polarity and malignant progression in tumors. Furthermore, we highlight emerging regulatory dimensions, including the dephosphorylation of the Par6 complex by phosphatases such as PP2A and PHLPP, which represent novel targets for therapeutic intervention. By integrating these aspects, this review provides a comprehensive and mechanistic framework for understanding the multifaceted roles of Par6 in cancer and underscores its potential as a diagnostic biomarker and therapeutic target.