TOX3 regulates the proliferation and apoptosis of colorectal cancer by downregulating RhoB via the activation of the MAPK pathway.

TOX high mobility group box family member 3 (TOX3) can function as tumor suppressor or oncogene in different tumors, while ras homolog family member B (RhoB) is a well-known tumor suppressor. The expression and role of TOX3 in colorectal cancer (CRC) are unknown. This study aimed to investigate the expression of TOX3 in CRC and the role of TOX3/mitogen-activated protein kinase (MAPK)/RhoB signaling in the proliferation and apoptosis of CRC cells. We showed that TOX3 messenger RNA (mRNA) and protein expression levels were significantly upregulated in CRC tissues and cell lines. High TOX3 expression was associated with high T stage, nodal invasion, and advanced tumor stage. Disease-free survival (DFS) was shortened for CRC patients with high expression of TOX3, while overall survival showed no significant difference. TOX3 promoted proliferation, inhibited apoptosis, and decreased the sensitivity to oxaliplatin of CRC cells. In addition, the inhibition of TOX3 led to the upregulation of RhoB, and RhoB overexpression suppressed the proliferation and promoted apoptosis of CRC cells. Moreover, TOX3 overexpression upregulated MAPK signaling, while MAPK signaling inhibitor U0126 induced CRC cell proliferation arrest or apoptosis, and attenuated the inhibition of RhoB in TOX3 overexpression cells. In addition, the overexpression of TOX3 increased tumor volume in nude mice. In conclusion, TOX3 may be an oncogene in CRC and can predict DFS in CRC patients. TOX3/MAPK/RhoB signaling plays an important role in the modulation of proliferation and apoptosis of CRC cells.