Cytokines produced in the tumour microenvironment exert an important role in
cancer pathogenesis and in the inhibition of
disease progression.
Cancer of the cartilage is termed metastatic
chondrosarcoma; however, the signaling events resulting in mesenchymal cell transformation to
sarcoma have yet to be fully elucidated. The present study aimed to characterize the
cytokine expression profile in the human JJ012
chondrosarcoma cell line, as well as the effect of
cytostatic proline-rich polypeptide-1 (PRP-1). Western blot experiments demonstrated that the levels of suppressor of
cytokine signaling 3 (SOCS3) were upregulated in chondrocytes compared with
chondrosarcoma cells. Addition of PRP-1 restored the expression of the
tumor suppressors, SOCS3 and ten-eleven-translocation methylcytosine
dioxygenase 1 and 2 (TET1/2), in a dose-responsive manner. It is known that methylation of
histone H3K9 was eliminated from the promoters of the
inflammation-associated genes. PRP-1 inhibited H3K9 demethylase activity with an IC50 (concentration required to give half-maximal inhibition) value of 3.72 µg/ml in the
chondrosarcoma cell line. Data obtained from ELISA experiments indicated that the expression of
interleukin-6 (IL-6) in
chondrosarcoma cells was 86-fold lower compared with that in C28 chondrocytes. In the present study, a 53-fold downregulation of
IL-6 expression in co-culture of
chondrosarcoma cells and C28 chondrocytes was identified as well. Downregulation of
IL-6 expression has been documented in numerous other
tumor types, although the reasons for this have not been fully established. In
chondrosarcoma,
IL-6 manifests itself as an
anti-inflammatory agent and, possibly, as an anti-tumorigenic factor. To explore
protein-
DNA interactions leading to such differences, a gel-shift chemiluminescent assay was performed. Gel shifts were observed for
chondrosarcoma and chondrocytes in the lanes that contained nuclear
cell extract and oligo-IL-6
DNA. Notably, the
DNA-
protein complexes in C28 chondrocytes were markedly larger compared with those in
chondrosarcoma cells. The mechanisms that underpin such differences, and characterization of the interacting
proteins, remain to be fully elucidated.