Mechanisms of acquired androgen independence during arsenic-induced malignant transformation of human prostate epithelial cells.

Background: Prostate cancer progression often occurs with overexpression of growth factors and receptors, many of which engage the Ras/mitogen-activated protein MAP kinase (MAPK) pathway.

Objectives: In this study we used arsenic-transformed human prostate epithelial cells, which also show androgen-independent growth, to study the possibility that chronic activation of Ras/MAPK signaling may contribute to arsenic-induced prostate cancer progression.

Methods: Control and chronic arsenic-transformed prostate epithelial cells (CAsE-PE) were compared for Ras/MAPK signaling capacities using reverse transcription-polymerase chain reaction and Western blot analyses.

Results: We found activation of HER-2/neu oncogene in transformed CAsE-PE cells, providing molecular evidence of androgen independence in the transformed cells. CAsE-PE cells displayed constitutively increased expression of unmutated K-Ras (6-fold), and the downstream MAP kinases A-Raf and B-Raf (2.2-fold and 3.2-fold, respectively). There was also increased expression of phosphorylated MEK1/2 and Elk1 in the transformant cells. The MEK1/2 inhibitor, U0126, blocked PSA overexpression in CAsE-PE cells.

Conclusion: Thus, arsenic-induced malignant transformation and acquired androgen independence are linked to Ras signaling activation in human prostate epithelial cells. Chronic activation of this pathway can sensitize the androgen receptor to subphysiologic levels of androgen. This may be important in arsenic carcinogenesis and provide a mechanism that may be common for prostate cancer progression driven by diverse agents.