casein-kinase-ii and Fibrosarcoma

Matrix metalloproteinase 2 (MMP-2) is involved in cancer development and is overexpressed in a variety of malignant tumors. MMP-2 activity is controlled mainly by transcription, proteolytic activation, and inhibition by endogenous inhibitors. It had previously been demonstrated that MMP-2 activity is also regulated by phosphorylation at several sites by protein kinase C. Here we demonstrate, by means of bioinformatics and biochemical and cellular assays, that protein kinase CK2 also acts as a modulator of MMP-2 activity. CK2 down-regulates MMP-2 in vitro, and inhibition of CK2 in human fibrosarcoma cells results in up-regulation of MMP-2. The discovery of the crosstalk between MMP-2 and CK2 opens the possibility of new combined anticancer therapies.

Topics: Casein Kinase II; Cell Line, Tumor; Computational Biology; Down-Regulation; Fibrosarcoma; Humans; Matrix Metalloproteinase 2; Matrix Metalloproteinase Inhibitors; Phosphorylation; Receptor Cross-Talk

Stanniocalcin 1 (STC1) and stanniocalcin 2 (STC2) are two recently identified mammalian peptide hormones. STC1 plays a role in calcium and phosphate homoeostasis, while the role of STC2 is unknown. We examined a human fibrosarcoma cell line, HT1080, that has high steady-state STC1 and STC2 mRNA levels, to determine whether these proteins are secreted. Following incubation of HT1080 cells with (32)P, labelled STC1 and STC2 were found to be secreted into the medium. STC1 was phosphorylated in vitro by protein kinase C (PKC). In vitro and in vivo phosphorylation both occurred exclusively on serine and the phosphopeptide maps were similar, suggesting that PKC might be the in vivo kinase. STC2 was phosphorylated in vitro by casein kinase II (CK2), in vitro and in vivo phosphorylation were exclusively on serine and the phosphopeptide maps were indistinguishable. Phosphorylation of STC2 in intact cells resulted from the action of an ecto-protein kinase, since exogenous STC2 was phosphorylated by HT1080 cells and no phosphorylated STC2 was detectable inside the cells. The ectokinase activity was abolished by heparin and GTP could substitute for ATP as the phosphate donor, indicative of an ecto-CK2-like activity. The in vitro CK2 phosphorylation site was shown by matrix-assisted laser-desorption ionization-time-of-flight MS to be a single serine located between Ser-285 and Ser-298 in the C-terminal region of STC2. This is the first report of the secretion of STC1 or STC2 from mammalian cells. We conclude that these human fibrosarcoma cells express both STC1 and STC2 as secreted phosphoproteins in vivo, with STC2 being phosphorylated by an ecto-CK2-like enzyme.

Topics: Blotting, Western; Casein Kinase II; Culture Media, Conditioned; Electrophoresis, Polyacrylamide Gel; Fibrosarcoma; Glycoproteins; Hormones; Humans; Immunohistochemistry; In Situ Hybridization; Intercellular Signaling Peptides and Proteins; Kinetics; Phosphorylation; Protein Kinase C; Protein Kinases; Protein Serine-Threonine Kinases; Recombinant Proteins; RNA, Messenger; Serine; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Tumor Cells, Cultured