Ameloblastoma (AB) is a benign yet locally aggressive odontogenic epithelial tumor, characterized by frequent recurrence and a potential for distant metastasis. The primary cilium (PC), a microtubule-based organelle that serves as a signaling hub for multiple oncogenic pathways, is typically reduced or absent in most human malignancies; however, its status in AB remains poorly defined. In this retrospective, tissue-based observational study, we investigated the presence of PC in 42 AB cases, encompassing all major histological subtypes, using immunohistochemistry, immunofluorescence, and ultrastructural techniques. As a comparator, 41 cases of oral squamous cell carcinoma (OSCC), a tumor originating from the same oral cavity region, were also analyzed. PC were consistently detected in all ABs but were absent in OSCCs. In ABs, the presence of PC was validated by multiple markers and imaging modalities. In conventional AB, the density of PC varies significantly among the histological patterns. Notably, the cilia frequently exhibited a polarized orientation in the peripheral columnar cells of the follicular subtype. PC were also present in recurrent and metastatic lesions, although their significance in disease progression remains uncertain. Elevated GLI1 mRNA expression, nuclear accumulation of GLI1, and elevated SHH mRNA and protein expression indicated the activation of the Hh signaling pathway in ABs. Transcriptomic screening of early ciliogenesis-related genes revealed selective upregulation of CEP164 in ABs but not in OSCCs or other PC-deficient carcinomas. CEP164 protein was significantly overexpressed and localized closely apposed to but only partially overlapped with γ-tubulin signals, consistent with its role at the distal appendages of the basal body. Functional analyses demonstrated that CEP164 overexpression promoted PC formation, whereas its knockdown suppressed ciliogenesis. These findings indicate that ABs uniquely preserve functional PC and implicate CEP164 as a key mediator of this phenotype, offering novel insights into AB biology and highlighting its potential as a diagnostic and therapeutic target.
Miyazaki et al. (Tue,) studied this question.