KIF5B

KIF5B Full Name

kinesin family member 5B

KIF5B Introduction

Timeless homolog (TIMELESS) is a core component of the circadian clock and DNA replication machinery that plays dual roles in the regulation of circadian rhythms and the maintenance of genomic stability. Encoded by the TIMELESS gene on chromosome 12q13.3 in humans, TIMELESS was initially identified in Drosophila as an essential circadian clock gene that partners with Period (PER) to mediate the negative feedback loop driving circadian oscillations. In mammals, TIMELESS retains circadian functions but has also acquired a critical role in the DNA damage response and replication fork stabilization, representing a remarkable example of functional diversification across evolution.

Figure 1. Strcuture of KIF5B.

Circadian Clock Function and DNA Replication Fork Protection
In the mammalian circadian clock, TIMELESS interacts with the core clock protein Cryptochrome (CRY) and PER proteins within the negative limb of the transcriptional-translational feedback loop that generates approximately 24-hour rhythms. TIMELESS promotes the nuclear accumulation of CRY proteins, facilitating the repression of CLOCK-BMAL1-driven transcription. Beyond its circadian role, TIMELESS is an essential component of the replication fork protection complex (FPC) that travels with the replisome during S phase. Together with its obligate partner Tipin (TIMELESS-interacting protein), TIMELESS stabilizes replication forks encountering obstacles and coordinates the activities of replicative DNA polymerases, the replicative helicase (CMG complex), and the intra-S phase checkpoint kinase ATR. Loss of TIMELESS results in replication fork collapse, excessive origin firing, and genomic instability. The TIMELESS-Tipin complex also interacts directly with the checkpoint mediator Claspin, facilitating CHK1 phosphorylation by ATR and thereby linking replication fork stability to cell cycle checkpoint activation.

TIMELESS in Cancer Biology, Chemotherapy Response, and Circadian Medicine
Given its dual role in DNA replication and circadian rhythms, TIMELESS has attracted considerable attention in cancer biology. TIMELESS is overexpressed in a wide range of human malignancies, including breast cancer, colorectal cancer, hepatocellular carcinoma, and lung cancer, where its elevated expression is frequently associated with poor prognosis. Cancer cells may exploit TIMELESS overexpression to sustain high replication rates and resist replication stress induced by oncogene activation and chemotherapy. TIMELESS knockdown sensitizes cancer cells to DNA-damaging agents including cisplatin and ionizing radiation, identifying it as a potential chemosensitization target. The circadian rhythmicity of TIMELESS expression also has implications for chronotherapy — the timing of chemotherapy administration relative to circadian gene expression rhythms to optimize efficacy and minimize toxicity. The intersection of TIMELESS biology with the circadian clock, DNA replication, and cancer cell survival makes it a compelling nexus for therapeutic intervention in oncology.

Alternate Names for KIF5B

KIF5B; kinesin family member 5B; KNS; KINH; KNS1; UKHC; HEL-S-61; kinesin-1 heavy chain; kinesin heavy chain; kinesin 1 (110-120kD); ubiquitous kinesin heavy chain; conventional kinesin heavy chain; epididymis secretory protein Li 61;