Overexpression of fatty acid synthase is associated with palmitoylation of Wnt1 and cytoplasmic stabilization of beta-catenin in prostate cancer.

Fatty acid synthase (FASN), a key metabolic enzyme for liponeogenesis highly expressed in several human cancers, displays oncogenic properties such as resistance to apoptosis and induction of proliferation when overexpressed. To date, no mechanism has been identified to explain the oncogenicity of FASN in prostate cancer. We generated immortalized prostate epithelial cells (iPrECs) overexpressing FASN, and found that (14)C-acetate incorporation into palmitate synthesized de novo by FASN was significantly elevated in immunoprecipitated Wnt-1 when compared to isogenic cells not overexpressing FASN. Overexpression of FASN caused membranous and cytoplasmic beta-catenin protein accumulation and activation, whereas FASN knockdown by short-hairpin RNA resulted in a reduction in the extent of beta-catenin activation. Orthotopic transplantation of iPrECs overexpressing FASN in nude mice resulted in invasive tumors that overexpressed beta-catenin. A strong significant association between FASN and cytoplasmic (stabilized) beta-catenin immunostaining was found in 862 cases of human prostate cancer after computerized subtraction of the membranous beta-catenin signal (P<0.001, Spearman's rho=0.33). We propose that cytoplasmic stabilization of beta-catenin through palmitoylation of Wnt-1 and subsequent activation of the pathway is a potential mechanism of FASN oncogenicity in prostate cancer.