The rearrangement of pre-existing genes has long been thought of as the major 
mode of new gene generation. Recently, de novo gene birth from non-genic DNA was 
found to be an alternative mechanism to generate novel protein-coding genes. 
However, its functional role in human disease remains largely unknown. Here we 
show that NCYM, a cis-antisense gene of the MYCN oncogene, initially thought to 
be a large non-coding RNA, encodes a de novo evolved protein regulating the 
pathogenesis of human cancers, particularly neuroblastoma. The NCYM gene is 
evolutionally conserved only in the taxonomic group containing humans and 
chimpanzees. In primary human neuroblastomas, NCYM is 100% co-amplified and 
co-expressed with MYCN, and NCYM mRNA expression is associated with poor 
clinical outcome. MYCN directly transactivates both NCYM and MYCN mRNA, whereas 
NCYM stabilizes MYCN protein by inhibiting the activity of GSK3β, a kinase that 
promotes MYCN degradation. In contrast to MYCN transgenic mice, neuroblastomas 
in MYCN/NCYM double transgenic mice were frequently accompanied by distant 
metastases, behavior reminiscent of human neuroblastomas with MYCN 
amplification. The NCYM protein also interacts with GSK3β, thereby stabilizing 
the MYCN protein in the tumors of the MYCN/NCYM double transgenic mice. Thus, 
these results suggest that GSK3β inhibition by NCYM stabilizes the MYCN protein 
both in vitro and in vivo. Furthermore, the survival of MYCN transgenic mice 
bearing neuroblastoma was improved by treatment with NVP-BEZ235, a dual 
PI3K/mTOR inhibitor shown to destabilize MYCN via GSK3β activation. In contrast, 
tumors caused in MYCN/NCYM double transgenic mice showed chemo-resistance to the 
drug. Collectively, our results show that NCYM is the first de novo evolved 
protein known to act as an oncopromoting factor in human cancer, and suggest 
that de novo evolved proteins may functionally characterize human disease.