¹Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA

Correspondence: SAG Reddy, Department of Gastrointestinal Medical Oncology, Unit 426, 1515 Holcombe Blvd, UTMD Anderson Cancer Center, Houston, TX 77030, USA. E-mail: sa08366@odin.mdacc.tmc.edu

Received 18 August 2003; Revised 19 March 2004; Accepted 11 May 2004; Published online 27 September 2004.

Abstract

The persistent activation of signaling cascades results in dramatic consequences that include loss of cellular growth control and neoplastic transformation. We show here that phosphoinositide 3-kinase (PI 3-kinase) and its mediator Akt were constitutively activated in pancreatic cancer and that this might be due to the aberrant expression of their natural antagonist MMAC/PTEN. Indeed, our results show that MMAC/PTEN expression was either lost or significantly reduced in five of eight cell lines and in twelve of seventeen tumor specimens examined. That the poor expression of MMAC/PTEN in pancreatic cancer cells could be due to promoter methylation was indicated by methylation-specific PCR analysis. Our studies also indicated that PI 3-kinase targeted two important transcription factors in pancreatic cancer cells. The ability of constitutively activated NF-B to induce gene expression and the stabilization of c-MYC protein by decreased phosphorylation of Thr58 were both dependent on PI 3-kinase activity. When pancreatic cancer cells were treated with a peptide antagonist of NF-B nuclear translocation, or stably transfected with a dominant-negative mutant of MYC, their proliferation was markedly inhibited. Taken together, these data indicate that the aberrant expression of MMAC/PTEN contributes to the activation of the PI 3-kinase/Akt pathway and its transcription factor mediators in pancreatic cancer.