Coordinate expression of the PI3-kinase downstream effectors serum and glucocorticoid-induced kinase (SGK-1) and Akt-1 in human breast cancer

The phosphatidylinositol 3-kinase (PI3-K) signalling pathway has been implicated in breast cancer development and resistance to therapy. Akt-1 and serum and glucocorticoid-induced kinase-1 (SGK-1) are homologous kinases which are important downstream effectors of PI3-K signalling. We sought to determine the individual expression patterns of these two kinases in order to better understand their respective roles in PI3-K signalling in breast cancer. To this end, we examined the expression of both p-Akt-1 and SGK-1 in 40 breast cancers. p-Akt-1 expression was seen in 58% of tumour samples, while SGK-1 overexpression was detected in 48%. Interestingly, a highly significant association was found between the expression of p-Akt-1 and SGK-1 (P = 0.002), suggesting complementary physiological functions in PI3-K signalling. This finding is consistent with recent genetic data from Caenorhabditis elegans suggesting that both SGK-1 and Akt-1 are required for signalling downstream of insulin receptor activation.