The Two-Way Role of Jagged1 in Cancer: A Focus on CRC.

Colorectal cancer (CRC) remains one of the most prevalent and lethal malignancies. Accumulating genetic evidence supports a multistep model of tumor progression, in which early APC loss leads to chromosomal instability and adenoma formation, followed by activating mutations in KRAS that synergize with β-catenin signaling to promote tumor growth and invasion. Among the downstream effectors of these pathways, the Notch ligand Jagged1 has emerged as a critical mediator of CRC progression and chemoresistance. Jagged1 is not only a transcriptional target of the Wnt/β-catenin axis but also undergoes proteolytic cleavage via the KRAS/ERK/ADAM17 signaling cascade, generating a nuclear Jagged1 intracellular domain (Jag1-ICD) that drives reverse signaling. This dual functionality, activating canonical Notch signaling and initiating reverse nuclear signaling, positions Jagged1 as a key oncogenic driver in CRC. In this review, we first summarize the role of Jagged1 as an integral part of canonical Notch signaling. We then focus on the non-canonical Jagged1 reverse signaling function in cancer, with a particular emphasis on CRC. We underscore the dual role of Jagged1 in tumor biology and propose that it functions as a novel oncogene within the adenoma-to-carcinoma sequence, supporting CRC development and drug resistance via non-canonical mechanisms.