Functional characterization of the progestagen-associated endometrial protein gene in human melanoma

Utilizing gene microarray profiling of melanoma samples, we have recently identified a novel gene overexpressed in both thick primary and metastatic melanomas. This gene, progestagen-associated endometrial protein (PAEP), has never before been implicated in the oncogenic processes of melanoma, with its true function in oncogenesis and tumour progression relatively unknown. Overexpression of the PAEP gene in freshly procured thick primary and metastatic melanoma samples (58%) and daughter cell lines (77%) is confirmed by quantitative RT-PCR, immunohistochemistry, Western blotting and mass spectrometric analysis. We suggest that PAEP gene overexpression is involved with melanoma tumour progression as well as an aggressive phenotype. Transfection of melanoma cells with PAEP small interfering RNA (siRNA) reveals a significant decrease in soft agar colony formation and a marked inhibition of both cell migration and cell invasion. Furthermore, we establish stable melanoma transfectants via PAEP lentiviral small hairpin RNA (shRNA), examine their growth characteristics in a murine xenograft model and reveal that tumour growth is significantly inhibited in two separate melanoma cell lines. Our data strongly implicate the PAEP gene as a tumour growth promoter with oncogenic properties and a potential therapeutic target for patients with advanced melanoma.