Cooperation between FGF8b overexpression and PTEN deficiency in prostate tumorigenesis

Two commonly occurring genetic aberrations of human prostate cancer [i.e., overexpression of a mitogenic polypeptide (fibroblast growth factor 8, isoform b or FGF8b) and loss of function of PTEN tumor suppressor] were recapitulated into a new combinatorial mouse model. This model harboring the Fgf8b transgene and haploinsufficiency in Pten, both in a prostate epithelium-specific manner, yielded prostatic adenocarcinoma with readily detectable lymph node metastases, whereas single models with each of the defects were shown earlier to progress generally only up to prostatic intraepithelial neoplasia (PIN). In addition to late age-related development of typical adenocarcinoma, the model also displayed a low incidence of mucinous adenocarcinoma, a rare variant type of human prostatic adenocarcinoma. The cooperation between FGF8b activation and PTEN deficiency must be linked to acquisition of additional genetic alterations for the progression of the lesions to primary adenocarcinoma. Here, we identified loss of heterozygosity at the Pten gene leading to bialleic loss, as a necessary secondary event, indicating that a complete loss of PTEN function is required in the development of invasive cancer in the model. Analyses of expression of downstream mediators phospho-AKT (p-AKT) and p27(KIP1), in various types of lesions, however, revealed a complex picture. Although PIN lesions displayed relatively strong expression of p-AKT and p27(KIP1), there was a notable heterogeneity with variable decrease in their immunostaining in adenocarcinomas. Together, the results further underscore the notion that besides activation of AKT by loss of PTEN function, other PTEN-regulated pathways must be operative for progression of lesions from PIN to adenocarcinoma.