N⁶-Methyladenosine Reader Protein YTHDC1 Supports Proper Mitotic Progression Partly through Regulation of TPX2–Aurora A Signaling

Abstract

Chemical modification of mRNA regulates its stability and translation efficiency. The most prevalent modification is the N⁶-methyladenosine (m⁶A) modification. YT521-B homology domain-containing proteins (YTHDCs) are “reader” proteins of m⁶A modification and contribute to various cell functions by regulating their target m⁶A-containing mRNAs. Although m⁶A modification dynamically changes throughout the cell cycle, the role of the m⁶A pathway in cell division remains unclear. In this study, we found that YTHDC1, one of the YTHDCs, is important for cell division. Mitotic progression is delayed in YTHDC1-knockdown cells, and the mitotic delay is mitigated by the re-expression of wild-type YTHDC1, indicating the YTHDC1 function in mitotic progression. Time-lapse imaging analysis showed that prolonged mitotic duration caused by YTHDC1 knockdown is due to the retardation of chromosome alignment and segregation. Treatment of AZ3146, an inhibitor of the spindle assembly checkpoint (SAC), mitigates the mitotic delay in YTHDC1-knockdown cells, suggesting that YTHDC1 knockdown results in SAC activation, leading to a slowdown of mitotic progression. Furthermore, increased TPX2 protein expression and the subsequent overabundance of Aurora A at the centrosomes is partly involved in YTHDC1 knockdown-induced mitotic delay. Since YTHDC1 knockdown does not affect the TPX2 mRNA level and the inhibition of protein synthesis by cycloheximide treatment impairs the YTHDC1-knockdown effect on the TPX2 protein level, YTHDC1 may post-transcriptionally regulate the TPX2 expression. Considering that TPX2 or Aurora A overexpression causes mitotic failure, these results suggest that YTHDC1 contributes to mitotic progression partly through the precise regulation of TPX2–Aurora A signaling.

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