Inflammatory breast cancer (IBC) is the most lethal form of locally advanced breast cancer. We found concordant and consistent alterations of two genes in 90% of IBC tumors when compared with stage-matched non-IBC tumors: overexpression of RhoC guanosine triphosphatase and loss of WNT-1 induced secreted protein 3 (WISP3). Further work revealed that RhoC is a transforming oncogene for human mammary epithelial (HME) cells. Despite the aggressiveness of the RhoC-driven phenotype, it does not quantitatively reach that of the true IBC tumors. We have demonstrated that WISP3 has tumor growth and angiogenesis inhibitory functions in IBC. We proposed that RhoC and WISP3 cooperate in the development of IBC.

Using an antisense approach, we blocked WISP3 expression in HME cells. Cellular proliferation and growth were determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and anchorage-independent growth in a soft agar assay. Vascular endothelial growth factor (VEGF) was measured in conditioned medium by enzyme-linked immunosorbent assay.

Antisense inhibition of WISP3 in HME cells increased RhoC mRNA levels and resulted in an increase in cellular proliferation, anchorage-independent growth and VEGF levels in the conditioned medium. Conversely, restoration of WISP3 expression in the highly malignant IBC cell line SUM149 was able to decrease the expression of RhoC protein.

WISP3 modulates RhoC expression in HME cells and in the IBC cell line SUM149. This provides further evidence that these two genes act in concert to give rise to the highly aggressive IBC phenotype. We propose a model of this interaction as a starting point for further investigations.