The online version of this article (https://doi.org/10.1186/s12943-017-0747-z) contains supplementary material, which is available to authorized users.
Protein kinase N2 (PKN2) is a PKC-related serine/threonine-protein kinase. PKN2 is required for tumor cell migration, invasion and apoptosis. However, the functional role of PKN2 in regulating tumor associated macrophages (TAMs) polarization in colon cancer has never been reported.
PKN2 expression in human colon cancer tissues was examined with immunohistochemistry (IHC). M1/M2 macrophage signatures were evaluated by RT-PCR, IHC and flow cytometry. The effects of PKN2 on tumor growth and TAM polarization were investigated both in vitro and in vivo. PKN2 targeted cytokines/pathway were analyzed by gene expression analysis and further confirmed by PCR, luciferase assay or western blot. Correlations between PKN2 and transcriptional factors for IL4 and IL10 were confirmed by ChIP-qPCR. The catalytic activities of PKN2 and DUSP6 were determined by kinase activity assay. Interactions between PKN2 and DUSP6 were confirmed by Co-IP.
The expression of PKN2 in colon cancer cells predicted a favorable prognosis and was associated with low M2 macrophage content in human colon cancer tissues. PKN2 inhibited tumor growth in mice xenograft model and inhibited M2 phenotype polarization both in vitro and in vivo. Mechanistically, PKN2 suppresses the expression of IL4 and IL10 from colon cancer cells by inhibiting Erk1/2 phosphorylation, which is required for phosphorylation and binding of CREB and Elk-1 to the promoters of IL4 and IL10. DUSP6, which is phosphorylated and activated through direct association with PKN2, suppresses Erk1/2 activation.
The expression of PKN2 in colon cancer cells suppresses tumor associated M2 macrophage polarization and tumor growth. Targeting PKN2 signaling pathway may provide a potential therapeutic strategy for colon cancer.
Additional file 1: Table S1. KEGG pathway analysis of differentially expressed genes in colon cancer cells with different PKN2 expression level. Figure S1. The effect of M1-like and M2-like macrophages on proliferation of colon cancer cells in vitro. Figure S2. The effect of cardiolipin stimulation on cell proliferation and induction of macrophages differentiation of colon cancer cells. Figure S3. The effect of colon cancer cells on macrophages differentiation with different effector/target ratios in vitro. Figure S4. The effect of differently polarized macrophages on tumor cell proliferation. Figure S5. Heatmap of the gene expression array for cells with different PKN2 expression levels. Figure S6. The transcriptional factors involved in PKN2 mediated IL4 and IL10 expression. (DOC 34011 kb)12943_2017_747_MOESM1_ESM.doc
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- PKN2 in colon cancer cells inhibits M2 phenotype polarization of tumor-associated macrophages via regulating DUSP6-Erk1/2 pathway
- BioMed Central
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