Knockdown of c-Jun N-terminal kinase 1 expression in murine mammary cancer cells leads to an increase in tumor growth and bone metastasis.

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Abstract Abstract #1156 The c-Jun N-Terminal Kinase (JNK) family of proteins are involved in cell proliferation and apoptosis depending on the specific isoform, cell type, and activating stimuli. The JNK proteins are known as the predominant c-Jun kinases, resulting in AP-1 activation and increased expression of AP-1 transcriptional targets. More specifically, it has been reported that osteoclast differentiation is impaired in jnk1-/- mice. The purpose of this study was to determine whether expression of JNK1 in cancer cells will influence the bone microenvironment during metastatic growth. The 4T1.2 murine mammary cancer cell line was studied as an established model for mammary cancer mediated bone metastasis. Using a JNK1α1 shRNA approach, we observed 75% reduction in expression Orthotopic injection of the shJNK1α1 cells into the mammary fat pad of Balb/c mice significantly increased tumor growth rates and shortened survival compared to the respective empty vector cell line (p<0.0001). Similarly, intra-cardiac injection of the shJNK1α1 cells led to a significant decrease in survival (p=0.003) and an increase in incidence of metastatic lesions in the ribcage (p=0.04). Serum levels of Cathepsin K were assayed as an indicator of bone resorption and was significantly higher in the mice injected with the knockdown cells compared to empty vector controls (p=0.03). Finally, immunohistochemical analysis of bone lesions showed higher expression of ADAM (A Disintegrin and Metalloproteinase) 10 suggesting that the more aggressive phenotype observed with the shJNK1a1 cells may be attributed to the increase in ADAM10 protein expression. Previous studies have shown that ADAM10 that cleaves RANKL into its active soluble form. Further, RANKL expression has been reported to be elevated in breast carcinomas, resulting in osteolysis during metastasis. Indeed our qPCR analysis detected an approximate 2 fold increase in RANKL levels in the shJNK1α1 cells, consistent with this assertion. In summary, these data support that reduction in JNK1a1 expression enhances bone metastasis and ADAM10 expression. We hypothesize that increased RANKL cleavage by ADAM 10 allows RANKL to bind its receptors expressed on nearby osteoclasts further perpetuating the vicious cycle of bone metastasis. These data suggest that bone metastasis may be controlled by inhibiting ADAM10 activity to reduce RANKL induced osteolysis and tumor progression. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1156.