Positive correlation between overexpression of phospho-BAD with phosphorylated Akt at serine 473 but not threonine 308 in colorectal carcinoma

The enhancement of cell proliferation and promotion of cell survival via the inhibition of apoptosis is thought to be the key to the initiation and progression of cancers. The phosphatidylinositol-3 kinase (PI3K)/Akt is an important survival signal pathway that has been shown to be crucial in the regulation of balance between pro-apoptotic and survival (anti-apoptotic) signal. In this study, the expression of phosphorylated Akt at Thr(308) and Ser(473), BCL-2-antagonist of cell death (BAD) at Ser(136) and glycogen synthase kinase-3beta (GSK-3beta) at Ser(9) in 47 paraffin-embedded human colorectal carcinoma (CRC) tissues were determined by immunohistochemical staining in order to dissect the alterations in the signal transduction pathways in CRC. Our results showed that there was a significant increase in the expression of these biomolecules in CRC tissues compared to the apparently normal adjacent tissues. The frequency of increased expression in tumor colonic mucosa were as follows: p-Akt1/2/3 (Thr(308)) = 16/47 (34%); p-Akt1 (Ser(473)) = 21/47 (44.7%); phospho-BAD (p-BAD) Ser(136) = 27/47 (57.4%) and phospho-GSK-3beta (p-GSK-3beta) = 21/47 (44.7%). Analysis of the total p-Akt1 (Ser(473)), p-Akt1/2/3 (Thr(308)), p-GSK-3beta (Ser(9)) and p-BAD (Ser(136)) score found that there was a statistically significant relationship with each other. A statistically significant positive linear relationship was found between total p-Akt (Ser(473)) score and total p-GSK-3beta (Ser(9)) score as well as with total p-BAD (Ser(136)) score. On the other hand, total p-Akt1/2/3 (Thr(308)) scores had a statistically significant positive linear relationship with p-GSK-3beta (Ser(9)) only. The Akt targets, p-GSK-3beta (Ser(9)) and p-BAD (Ser(136)) were positively correlated to each other. There was no significant correlation between clinico-pathological data with total p-Akt1 (Ser(473)), p-Akt1/2/3 (Thr(308)), p-GSK-3beta (Ser(9)) and p-BAD (Ser(136)) score except for age. The total scores of p-GSK-3beta were found to be higher in patients in the age group of greater than 60. This is the first report of p-Akt1/2/3 (Thr(308)) and p-BAD (Ser(136)) expression in primary colorectal tumor tissue. Our data further supports the role of PI3K/Akt signaling pathways in the pathogenesis of CRC and contributes to the identification of target molecules in the signal transduction pathway for cancer therapy. (C) 2004 Elsevier Ireland Ltd. All rights reserved.