Investigating the role of a novel tumor suppressor gene, TUSC1, in colorectal cancer

Cancer stem cells (CSC) possess self-renewal, differentiation and drug resistance potential and are a promising target for anticancer therapy. While elucidating the role of CSC in colorectal cancer (CRC) using gene expression analysis, we discovered unique gene signature for CRC-CSC. In this study we elucidate the role of one of these genes, TUSC1, Tumor Suppressor Candidate 1 in CRC. TUSC1 expression was analyzed in tumor and control tissues of 70 CRC patients by immunohistochemistry (IHC). TUSC1 expression was evaluated in a panel of human CRC cell lines (HT29, HCT116, Caco2 and SW480) using qPCR and western blotting. Gain and loss of function of TUSC1 was studied using overexpression vector transfection and siRNA mediated gene silencing. Metabolic phenotyping of transfected and control CRC cells was done using metabolic flux analyzer (Agilent, XFe24). There was a difference in TUSC1 expression in tumor and control tissues as well as CRC cell lines (basal as well as after gain and loss of function). Using modulators of respiration that target components of the ETC in mitochondria, TUSC1 over-expressing cancer cells were found to have higher Oxygen Consumption Rate (OCR) and increased Extracellular Acidification Rate (ECAR). This increase in OCR and ECAR was abolished when TUSC1 was silenced using siRNA. Hence, TUSC1 over expression metabolically altered (increased mitochondrial respiration, ATP production and glycolytic capacity) cancer cells. In conclusion, modulating TUSC1 may be a promising modality to target chemo-resistant and radio-resistant CSC.