PTEN alterations of the stromal cells characterise an aggressive subpopulation of pancreatic cancer with enhanced metastatic potential.

BACKGROUND

Neoplastic stroma is believed to influence tumour progression. Here, we examine phosphatase and tensin homolog deleted on chromosome ten (PTEN) status in the tumour microenvironment of pancreatic ductal adenocarcinoma (PDAC) focussing especially at the stromal cells.

METHODS

We asses PTEN at protein, messenger RNA and DNA level using a well-characterised PDAC cohort (n = 117). miR-21, known to target PTEN, is assessed after RNA extraction from different laser-capture-microdissected cell populations, including cancer cells and juxta-tumoural and tumour-remote stroma.

RESULTS

PTEN deletion was the most frequent cause of PTEN protein loss in PDAC cells (71%) and correlated with vascular invasion (p = 0.0176) and decreased overall survival (p = 0.0127). Concomitant PTEN protein loss in tumour and juxta-tumoural stroma, found in 21.4% of PDACs, correlated with increased distant metastasis (p = 0.0045). Stromal cells with PTEN protein loss frequently showed PTEN genetic aberrations, including hemizygous PTEN deletion (46.6%) or chromosome 10 monosomy (40%). No alterations were found in the tumour-remote stroma. miR-21 was overexpressed by cancer- and juxta-tumoural stromal cells, in some cases without simultaneous PTEN gene alterations. No PTEN mutations or promoter methylation were detected.

CONCLUSIONS

We find various mechanisms of PTEN protein loss in the different tumour cell populations, including allelic PTEN deletions, gross chromosomal 10 aberrations and altered miR-21 expression. PTEN deletion is a major cause of PTEN protein loss in PDAC and correlates with aggressive characteristics and worse outcome. PTEN protein loss in juxta-tumoural stromal cells is mostly due to PTEN haplo-insufficiency and characterises a subgroup of PDACs with enhanced metastatic potential. In the tumour microenvironment of the invasive front, PTEN silencing by miR-21 in cancer and surrounding stromal cells acts not only cooperatively but also independently of the genetic aberrations to precipitate PTEN protein loss and promote further tumour growth.