A Meiotic B-type Cyclin Selectively Drives Mitotic Progression and Fidelity in Cancer Cells.

Cell cycle transitions are driven by cyclins in complex with cyclin-dependent kinases (CDK). Here, we demonstrate that cyclin B3, an evolutionarily divergent B-type cyclin previously thought to function exclusively in female meiosis, is expressed in mitotic cells and interacts with both CDK1 and CDK2. We show that cyclin B3-CDK1/2 is essential for timely mitotic progression by ensuring proper chromosome alignment and stable kinetochore-microtubule interactions, while its overexpression accelerates mitosis and improves chromosome alignment kinetics. Through phospho-mass spectrometry, we identify several kinetochore and mitotic spindle components as substrates of cyclin B3-CDK1/2 in mitosis. Notably, cyclin B3 depletion disrupts mitotic progression in most cancer cell lines tested - including colorectal, osteosarcoma, and breast cancer models - while non-transformed cells are largely unaffected. These findings identify cyclin B3-CDK1/2 as a novel driver of mitotic progression and reveal a preferential dependency in a subset of cancer cells that may represent a potential therapeutic vulnerability.