WISP3 and RhoC guanosine triphosphatase cooperate in the development of inflammatory breast cancer

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 to stage matched, non-IBC tumors: overexpression of RhoC GTPase and loss of WISP3. Further work revealed that RhoC is a transforming oncogene for 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 hypothesized that RhoC and WISP3 cooperate in the development of IBC.

Using an antisense approach, we blocked WISP3 expression in HME cells (HME/AS WISP3). Cellular proliferation and anchorage independent growth were determined using the MTT assay and the anchorage independent growth in soft agar assay. VEGF was measured in the conditioned media of the HME/ AS WISP3 by ELISA.

Antisense inhibition of WISP3 expression in HME cells increased the levels of RhoC mRNA and increased cellular proliferation, anchorage independent growth and secretion of VEGF in these cells. 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, and provide further evidence in support 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.