Wataru Heshiki, Kei Tomihara, Manabu Yamazaki, Naoya Arai, Kenji Nakamori and Makoto Noguchi
Background: Although caspase-3 is a key molecule for apoptosis induction, recent evidence has suggested its protumoral role in various human malignancies. The aim of the present study was to investigate the expression of cleaved caspase-3 (the active form of caspase-3) in both clinical samples and cell lines from oral squamous cell carcinomas (OSCCs) and elaborate on its contribution to the protumor role in oral cancer.
Methods: The expression of cleaved caspase-3 was immunohistochemically evaluated in samples from 30 patients with OSCCs. The samples were either from biopsies or surgically-resected specimens with a mix of clinical stages and tumor site origins. The expression of cleaved caspase-3 was further examined in three OSCC cell lines.
Results: In addition to apoptotic cancer cells, all the cases of OSCCs demonstrated a surprisingly positive expression of cleaved caspase-3. A diffuse, cytoplasmic pattern was particularly prominent in in situ carcinoma cells, invasive carcinoma cells, and metastatic cancer cells that lacked apoptotic morphology. On the other hand, non-neoplastic, normal epithelial cells were completely negative for cleaved caspase-3. In all the OSCC cell lines studied, cleaved caspase-3 was expressed in the cytoplasm and nucleus of cancer cells. Flow cytometric analysis also confirmed that the activation level of caspase-3 in non-apoptotic cancer cells was relatively lower than that in apoptotic cancer cells. Moreover, caspase-3 inhibition by caspase-3 specific inhibitor decreased the proliferation of OSCC cells.
Conclusions: Because cleaved caspase-3 is selectively expressed in non-apoptotic OSCC cells and is associated with cell proliferation, these findings implicate caspase-3 signaling in promoting the progression of oral cancer.
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