Clinical relevance of gene expression in localized and metastatic prostate cancer exemplified by FABP5.

PURPOSE

Fatty acid-binding protein 5 (FABP5), a transport protein for lipophilic molecules, has been proposed as protein marker in prostate cancer (PCa). The role of FABP5 gene expression is merely unknown.

METHODS

In two cohorts of PCa patients who underwent radical prostatectomy (n = 40 and n = 57) and one cohort of patients treated with palliative transurethral resection of the prostate (pTUR-P; n = 50) FABP5 mRNA expression was analyzed with qRT-PCR. Expression was correlated with clinical parameters. BPH tissue samples served as control. To independently validate findings on FABP5 expression, three microarray and sequencing datasets were reanalyzed (MSKCC 2010 n = 216; TCGA 2015 n = 333; mCRPC, Nature Medicine 2016 n = 114). FABP5 expression was correlated with ERG-fusion status, TCGA subtypes, cancer driver mutations and the expression of druggable downstream pathway components.

RESULTS

FABP5 was overexpressed in PCa compared to BPH in the cohorts analyzed by qRT-PCR (radical prostatectomy p = 0.003, p = 0.010; pTUR-P p = 0.002). FABP5 expression was independent of T stage, Gleason Score, nodal status and PSA level. FABP5 overexpression was associated with the absence of TMPRSS2:ERG fusion (p < 0.001 in TCGA and MSKCC). Correlation with TCGA subtypes revealed FABP5 overexpression to be associated with SPOP and FOXA1 mutations. FABP5 was positively correlated with potential drug targets located downstream of FABP5 in the PPAR-signaling pathway.

CONCLUSION

FABP5 overexpression is frequent in PCa, but seems to be restricted to TMPRESS2:ERG fusion-negative tumors and is associated with SPOP and FOXA1 mutations. FABP5 overexpression appears to be indicative for increased activity in PPAR signaling, which is potentially druggable.