Overexpression and activation of Akt2 protein in oral squamous cell carcinoma.

Aberrations of signal transducers in PI3K/Akt pathway have been found in many human cancers, and may play a critical role in carcinogenesis. Advanced research on oral cancer treatments, using novel agents targeting the PI3K/Akt signaling pathway, is being investigated with promising results. The objectives of this study were (1) to investigate expression of pan-Akt and its phosphorylated form (p-Akt), Akt1, and Akt2 in oral squamous cell carcinoma (OSCC) specimens (n=20) by immunohistochemistry, and (2) to determine mRNA expression of three Akt isoforms, including Akt1, Akt2, and Akt3, as well as their respective proteins, in five oral cancer cell lines and normal human oral keratinocytes (HOKs) by RT-PCR and Western blot assays. The results show that pan-Akt was expressed in 80% of OSCC cases, while Akt1, Akt2, and p-Akt were expressed in all OSCC cases. An intense expression of p-Akt at the invasive fronts of some OSCC samples was observed. Consistent with the immunohistochemical findings, p-Akt and Akt2 were overexpressed in all oral cancer cell lines in comparison with HOKs, whereas Akt2 mRNA was constitutively expressed, suggesting post-transcriptional regulation. In contrast, Akt1 mRNA and protein were constitutively expressed in all oral cancer cell lines and HOKs, while Akt3 mRNA appeared to be minimally expressed. In summary, these findings demonstrate that Akt2 and p-Akt are overexpressed in OSCC and may be involved in carcinogenesis, and suggest that post-transcriptional modification of Akt2 in OSCC may occur.