Functional analysis of altered Tenascin isoform expression in breast cancer

Background

Cellular interactions with the extracellular matrix (ECM) control many aspects of cell function. The complex ECM protein Tenascin-C (TN), which exists as multiple isoforms, is upregulated in breast cancer. We previously have identified a change in the TN isoform profile in breast cancer, with detection of two additional isoforms — TN16 and TN14/16 — not seen in normal breast [1]. The purpose of this study was to investigate directly the effects of these tumour-associated TNC isoforms on breast cancer cell behaviour.

Methods

A PCR-ligation approach was used to generate specific TNC isoform sequences which were Flag tagged and inserted into a pCMV vector. Transient transfection into breast cancer cell lines or primary normal fibroblasts was confirmed by RT-PCR, western blotting and immunohistochemistry. The effect of different TNC isoforms on breast cancer cell invasion, proliferation and gene expression was analysed.

Results

Expression of TN16 and TN14/16 in breast cancer cells (MCF-7, T47D, MDAMB231) resulted in significantly enhanced tumour invasion compared with adult-type truncated TN, large TN and vector-only controls. A similar increase in tumour cell proliferation was detected. Coculture of tumour cells with primary breast fibroblasts overexpressing TN16 or TN14/16 or conditioned medium from these fibroblasts also led to enhanced tumour cell invasion. Expression of TN resulted in upregulation of MMP-1; however, this was equivalent for all TN isoforms. The invasion-promoting effect of TN16 and TN14/16 was dependent on direct interaction between tumour cells and was blocked by incorporation of anti-TN blocking antibodies. Furthermore, TN appears to be essential for tumour cell invasion, since with all isoforms invasion was minimal in the presence of anti-TN antibodies.

Conclusion

This study has demonstrated that the tumour-associated TN isoforms TN16 and TN14/16 significantly enhance breast cancer cell invasion and that blocking TN inhibits invasion. We aim to further investigate the invasion-promoting activity of these isoforms and to explore their therapeutic potential in more sophisticated tumour models.