ING4 Tumor Suppressor and Chemotherapy Response in Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) is defined by the lack of three receptors (estrogen, progesterone, and HER2 receptors) and accounts for 12-17% of breast cancers. TNBC is an aggressive form of the disease associated with high rates of recurrence and mortality within five years. Inhibitor of Growth 4 (ING4) is a gene deleted in 16.5% and downregulated in 34% of breast tumors. The correlation between ING4 deficiencies and advanced tumors and poor patient survival implicates its tumor suppressive function in breast cancer. Low ING4 expression has been correlated with NFκB activation in metastatic breast tumors. Moreover, ING4 has been shown to inhibit NFkB-mediated gene transcription in various cancers, suggesting that ING4 may suppress cancer by inhibiting NFkB activation. However, the contribution of ING4 deficiencies and NFkB activation to aggressive TNBC progression is currently not well understood. We investigated the role of ING4 in the MDAmb231 TNBC cell line by genetically engineering the cells to overexpress or delete ING4. Cell growth and sensitivity to the chemotherapeutic agent doxorubicin were evaluated between the ING4-modified cell lines with or without TNFα to activate NFκB. The results showed that cell growths were comparable between the vector controls and ING4 overexpressing or deleted cell lines. In addition, TNFα treatment did not alter the growths of all cell lines, indicating that ING4 with or without NFkB activation did not play a role in determining the growth rates of TNBC. However, ING4 overexpressing cells were 20-30% more sensitive to 10 μM doxorubicin treatment, whereas ING4-deleted cells were 20-50% more resistant, suggesting that ING4 may determine chemotherapy response in TNBC. These findings suggest that tumors with low levels of ING4 may be more resistant to chemotherapy, thus requiring higher dosage and/or additional chemotherapy in patient treatment. Unexpectedly, TNFα sensitized all cell lines to doxorubicin regardless of ING4 expression levels, suggesting a TNFα function outside of NFκB activation in increasing doxorubicin sensitivity. It implicates that TNFα treatment may increase chemotherapy response in TNBC patients.