Mechanisms involved in tumor progression

S100A4 in invasion and metastasis

The biological function and molecular mechanisms by which S100A4 exerts its putative metastasis-promoting effects is largely unknown, and the protein is most likely involved in several aspects of tumor progression. One possible explanation for the multifunctionality is the fact that the protein is localized in different subcellular compartments and probably has different binding partners in the cytoplasm, the nucleus and in the extracellular space. In addition, the protein might also have different posttranslational modifications.

In the cytoplasm S100A4 co-localizes or co-sediments with different cytoskeletal proteins (actin, non-musclemyosin, and non-muscle tropomyosin), implying a possible role in cell motility and invasion. The protein has a wide variety of extracellular effects, including sensitization of osteosarcoma cells to IFN-g mediated apoptosis [Pedersen, BMC Cancer, 2004], stimulation of angiogenesis [Ambartsumian, Oncogene, 2001; Semov, JBC, 2005] and invasion through induction of matrix metalloproteinases [Schmidt-Hansen, Oncogene, 2004] and thereby promotion of metastasis [Schmidt-Hansen, JBC, 2004]. While strong data indicate that release of S100A4 into the tumor microenvironment is a crucial factor in the metastatic process, the signal transduction pathways responsible for S100A4-induced effects are only starting to become unraveled.

Extracellular effects of S100A4

In a previous study we demonstrated S100A4-induced activation of the transcription factor NFkB through the classical NFkB pathway in a subset of human cancer cell lines (Boye, Int. J. Cancer, 2008).. The intracellular signal transduction events leading to IKK phosphorylation and subsequent degradation of IkBa are poorly characterized. We seek to identify S100A4-induced signal transduction mechanisms upstream of the IKK complex. Such knowledge may provide important insight into S100A4 mediated signalling and thereby reveal possible targets for intervention. For more information contact Ida Grotterød or Kjetil Boye.

 We are currently investigating further potential downstream metastasis promoting effects of extracellular S100A4. In these studies, the effect of S100A4 on the levels or activity of MMPs and TIMPs, in addition to other known tumor metastasis promoting proteins are investigated in sarcoma cell lines by reverse transcriptase PCR, western-blotting, zymography and effect on biological activity such as invasion and migration. For more information contact Gisle Berge.

Posttranslational modifications of S100A4

Posttranslational modifications (PTM) of proteins may be of importance for both protein function and localization. Evidence derived from 2D-gel analyses indicates that S100A4 protein isolated from colorectal cancer cell lines and tumor biopsies has been modified by PTMs (Haugen et al., BMC Cancer, 2008). At present, we are in the process of identifying the PTMs in question using different proteomic strategies and further assess their potential biological importance. For more information contact Mads Haugen.

S100A4 and proteases

The mechanism by which S100A4 enhance protease activity is not known. Legumain is a recently identified cystein proteinase that can modify pro-MMP2 into active MMP2 by specific cleavage of asparaginyl bonds (Chen et al, 2001). Legumain is primarly localized in lysosomes, but has recently been reported to appear extracellularly associated with matrix and cell surfaces in the acidic tumor microenvironment (Wu et al, 2006). An association between expression of the protein and poor prognosis has been suggested for patient with breast (Gawenda et al., 2007) and colorectal cancer (Murthy et al, 2005).
We have recently started to investigate the possible link between legumain and S100A4. Furthermore, we are in collaboration with Profs. Harald Thidemann Johansen and Rigmor Solberg (School of Pharmacy, University of Oslo) and the department of Pathology, characterizing legumain and its involvement in tumor progression. Previous research by us and others, have demonstrated an association between the expression of S100A4, activity of matrix metalloproteinases (MMPs) and cellular metastatic capacity [Bjornland, K. et al. Cancer Res. 1999]. Furthermore, this regulation was suggested to involve NF-κB [Mathisen et al. Clin. & Exp. Metastasis, 2003]. MMPs and their endogenous inhibitors (tissue inhibitors of MMPs; TIMPs) have been shown to correlate with in vitro invasiveness and clinical outcome in several adult malignancies.  For more information contact Mads Haugen.

S100A4 as a prognostic factor

A number of reports have demonstrated that S100A4 expression could be used as a prognostic factor in a variety of different cancer types. We have shown that S100A4 protein expression was correlated with disease-free survival in melanoma patients (Andersen, Mod Pathology, 2004). In addition, we have demonstrated that S100A4 is also expressed in the nuclei of tumor cells from patients with colorectal cancer, and that the nuclear expression of S100A4 correlates with tumor stage (Flatmark, J Pathol, 2003). We are currently exploring the prognostic impact of nuclear and cytoplasmic S100A4 expression in this cohort of colorectal cancer patients. Recently, we have also developed an immunofluorometric assay for analysing S100A4 in serum, plasma or other body fluids (Flatmark, Tumor Biol, 2004). Unfortunately, the high expression level of S100A4 in both red and white blood cells precluded the use of S100A4 as a tumor marker in serum or plasma.