NUPR1 and colorectal cancer: Cell proliferation, which is the most prominent characteristics of HERV-K env gene KO cells, was significantly reduced by treatment of siRNA of nupr1 gene, with these results suggesting that reduced level of nupr1 gene by HERV-K env KO induces the RB protein expression to inhibit cell growth in DLD-1 colorectal cancer cells (Figure 6b).