{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRecent studies have demonstrated that protocadherin 9 (PCDH9) functions as an important tumor suppressor in several malignancies. In gliomas, for example, normal brain tissues exhibit strong PCDH9 expression that is markedly down‐regulated in tumors; this loss correlates with higher histological grade and poorer patient survival. Comparable patterns have been described in hepatocellular carcinoma and gastric cancer, where PCDH9 downregulation is associated with enhanced tumor cell migration, invasion, and features of epithelial–mesenchymal transition, while restoration of its expression impedes cell proliferation by inducing cell cycle arrest."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "4"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nMultiple regulatory mechanisms contribute to the dysregulation of PCDH9. In gliomas, for instance, miR‑215‑5p has been shown to target both the promoter and 3′UTR of the PCDH9 gene, leading to decreased mRNA and protein levels, which promotes cell proliferation, clonogenicity, and migration. Additionally, genomic analyses have identified a risk single-nucleotide polymorphism in PCDH9 that is associated with reduced expression and an increased risk of major depressive disorder, suggesting a role beyond oncogenesis. Moreover, the E3 ubiquitin ligase COP1 mediates Lys48‑linked polyubiquitination of PCDH9, targeting it for proteasomal degradation in glioma cells and thereby further diminishing its tumor suppressor function."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "5", "end_ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its role in tumor suppression, PCDH9 appears to be implicated in additional pathological contexts. In ovarian cancer, altered PCDH9 expression is among several factors that may contribute to the development of chemoresistance. Likewise, during human kidney development, reduced PCDH9 expression—for example, in cases of horseshoe kidney—suggests that its normal function in limiting cell migration is compromised, possibly contributing to congenital anomalies of the kidney and urinary tract. These diverse findings underscore the multifaceted roles of PCDH9 in regulating cell adhesion, migration, and signaling both in cancer and in developmental disorders."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Chunlin Wang, Guanzhen Yu, Jiachuan Liu, et al. 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