NELF prevents transcriptional readthrough into DNA replication zones in cancer cells.

Regulation of RNA polymerase II (Pol II) transcription is closely associated with cell proliferation. However, it remains unclear how the Pol II transcription program is rewired in cancer to promote uncontrolled growth. Here, we find that expression of NELFCD, a known negative transcription elongation factor, is upregulated in colorectal tumors. Auxin-dependent protein degradation of NELF-C in combination with nascent transcript sequencing demonstrates a direct role of NELF-C on Pol II transcription in this cancer. Strikingly, we demonstrate that the acute loss of NELF-C protein globally redistributes termination factors and perturbs Pol II transcription termination. These changes drive pervasive Pol II transcription into DNA replication zones, leading to transcription-replication conflict that may block the cell cycle in G1 or early S phase. Our findings reveal a previously unrecognized role of NELF in transcription termination and highlight NELF as a potential therapeutic target in colorectal cancer.