Reduced PTEN expression in the pancreas overexpressing transforming growth factor-beta 1

Abstract

PTEN is a candidate tumour suppressor gene and frequently mutated in multiple cancers, however, not in pancreatic cancer. Recently, it has been demonstrated that PTEN expression is regulated by TGF-beta1. Using TGF-beta1 transgenic mice (n=7) and wildtype littermates (n=6), as well as pancreatic tissues obtained from organ donors (n=10) and patients with pancreatic cancer (n=10), we assessed the expression of PTEN by means of immunohistochemistry and semiquantitative PCR analysis. In addition, PANC-1 cells were treated with TGF-beta1 in vitro and the levels of PTEN mRNA were determined in these cells. In human pancreatic cancers PTEN mRNA levels were significantly decreased (P<0.05). In addition, in the pancreas of TGF-beta1 transgenic mice the expression of PTEN was significantly reduced (P<0.01), as compared to wildtype littermates and incubation of PANC-1 cells with TGF-beta1 decreased PTEN mRNA levels after 24 h. Inasmuch as TGF-beta1 decreases PTEN expression in human pancreatic cancer cells and human pancreatic cancers overexpress TGF-beta1, the reduced expression of PTEN in pancreatic cancer may be mediated by TGF-beta1 overexpression. Thus, although PTEN is not mutated in pancreatic cancers, the reduction of its expression may give pancreatic cancer cells an additional growth advantage.

Figure 1

Immunohistochemical analysis of PTEN expression in pancreatic cancer. (A) In human pancreatic cancers PTEN immunoreactivity was present in some of the cancer cells. (B) Sections incubated with the anti-PTEN antibody and the blocking peptide exhibited no PTEN immunoreactivity.

Figure 2

RT–PCR analysis of PTEN mRNA levels in a pancreatic cancer cell line, in human and murine pancreas. (A) Semiquantitative analysis revealed decreased expression of PTEN mRNA in pancreatic cancers (right) as compared to the normal pancreas (left). Last lane, DNA ladder. (B) In transgenic mice overexpressing TGF-β1 (TGF-β1 tg) PTEN mRNA levels were also decreased as compared to wildtype littermates (wildtype). Last lane, DNA ladder. (C) Densitometric analysis confirmed a significant reduction of PTEN mRNA levels in pancreatic tumours (T) as compared to the normal pancreas (N) and in TGF-β1 transgenic mice (Tg) as compared to wildtype mice (Wt). Mean ±s.d.; □, PTEN mRNA levels as determined by densitometric analysis and standardization against their respective enolase mRNA or GAP mRNA levels; ★, P<0.05. (D) Incubation of PANC-1 cells with TGF-β1 led to a significant reduction of PTEN mRNA levels after 24 h, however not after 12 h. +, addition of TGF-β1; −, control without agonist addition; M, DNA ladder.