Evidence for PTEN-independent Akt activation and Akt-independent p27Kip1 expression in advanced bladder cancer

Abstract

In the treatment of advanced bladder cancer (BC), attention has recently focused on small molecule therapy concerning EGFR and the downstream Akt signalling pathway. Cellular deregulation processes are poorly understood, and biological determinants for the selection of therapy and monitoring are currently not available. The proteins PTEN, p-Akt and p27(Kip1) are suggested to be potentially significant biomarkers of Akt signalling. In this study, we investigated the expression of these proteins in advanced BC. PTEN, p-Akt and p27(Kip1) expression was determined immunohistochemically in 86 T2-4 BC specimens using a tissue microarray technique. Staining was documented with regard to intensity, cellular frequency and a multiplied staining score. Staining characteristics of the three proteins were correlated by regression analysis with the parameters of tumour stage and grade. A positive correlation was observed in the expression scores of PTEN and p-Akt, p-Akt and p27(Kip1) as well as PTEN and p27(Kip1) (p<0.02 for all combinations). The positive correlation between PTEN and p-Akt resulted mainly due to the strong correlation of PTEN intensity with p-Akt (p=0.0003 and p=0.0006 to p-Akt frequency and intensity, respectively). A positive correlation between p-Akt and p27(Kip1) was noted for p-Akt frequency as well as intensity (p<0.05 for all combinations). The positive correlation between PTEN and p27(Kip1) resulted due to the correlation of PTEN intensity alone with p27(Kip1) (p<0.03 for p27(Kip1) frequency and intensity), whereas no significance was noted for PTEN frequency. No correlation was found between T or G and expression of the proteins. However, activation of Akt in BC is known to occur independently of PTEN protein loss and appears not to cause a decrease of p27(Kip1). However, a direct regulatory impact of PTEN on p27(Kip1) was found. PTEN intensity, rather than frequency, appears to be a superior biomarker. These results may provide information to support research into protein profiling-predicted targeted therapy for BC. Correlations to benign urothelium, superficial BC specimens and follow-up data remain to be investigated.