Prostate cancer (PCa) is the most common cancer in men over the age of 50 with a predilection to metastasise to bone in advanced stages. It has been previously observed that the Wnt-inhibitor Dickkopf-1 (DKK-1) is differentially expressed in bone metastasising cancers, directing the osteolytic or osteoblastic phenotype. P38 MAPK (p38) activity is also dysregulated in patients with advanced stages of prostate cancer and has previously been shown to regulate DKK-1 in multiple myeloma. This in vitro study seeks to clarify the regulatory function of DKK-1 by p38 in PCa and how this may impact the phenotype of the induced bone lesions. DKK-1 was minimally expressed in MDA-PCa2b and C4-2B cell lines which are known to induce osteoblastic and mixed lesions in vivo, respectively. In contrast, the osteolytic PC3 cells have a high level of DKK-1 expression as measured by qPCR and by ELISA (p<0.005). Treatment of the osteoblastic cell line C2C12 with supernatants of PC3 cells led to a significant suppression of Wnt3a inducible osteoblastic markers including alkaline phosphatase (ALP) and osteoprotegerin (OPG). Strikingly, there was a strong rescue effect by neutralising DKK-1 with an antibody (anti-DKK-1) or knocking down DKK-1 expression using siRNA. Anisomycin, an activator of the MAPK signalling pathway, significantly increased (p<0.01) the expression of DKK-1, whereas p38 inhibitors LY2228820 and SB202190 significantly decreased DKK-1 (p<0.0001) expression in PC3 cells. General knockdown of p38 in PC3 cells using siRNA further confirmed the link between p38 and DKK-1 expression (p<0.0001). These results indicate the regulation of DKK-1 by p38 in osteolytic PCa cells and future investigations may strengthen the role of both DKK-1 and p38 activity as novel therapeutic targets in PCa-induced osteolytic bone lesions.
Disclosure: The authors declared no competing interests. This work was supported by the Deutschen Forschungsgemeinschaft (DFG) (grant numbers RA-2151/2-1, RA-1923/5-1).