Layilin promotes mitochondrial fission by cyclin-dependent kinase 1 and dynamin-related protein 1 activation in HEK293T cells.

Object: Functions of layilin, a type 1 transmembrane protein with a C-type lectin motif, remain to be clarified. We here investigated precise intracellular localization of layilin and the location-related functions.

Methods: We used HEK293T cells to assess the co-localization of layilin with different individual organelle markers by double immunostaining. We then investigated mitochondrial morphology in layilin-knockdown (KD) conditions, also with immunostaining. Next, we measured amounts of proteins involved in regulation of mitochondrial dynamics, DRP1, pS616-DRP1, mitofusin1, mitofusin2, CDK1, pY15-CDK1, and cyclin B1, in layilin-KD cells versus control cells by Western blot. Furthermore, by using layilin-knockout (KO) cells, amounts of CDK1 and pY15-CDK1 as well as mitochondrial morphology were investigated.

Result: We found that layilin localized to mitochondria rather than the other organelles. Small round-shape mitochondria were observed in control cells, whereas elongated and highly connected mitochondria were observed in layilin-KD cells. Amounts of active DRP1 (pS616-DRP1) and total DRP1 were significantly smaller in layilin-KD cells than in controls. Amounts of inactive CDK1 (pY15-CDK1) were significantly larger in layilin-KD cells than in controls. No other tested molecules were significantly altered in layilin-KD cells. Amounts of inactive CDK1 were significantly larger in layilin-KO cells than in wild type (WT) cells. Small round-shape mitochondria were observed in WT cells, whereas elongated and highly connected mitochondria were observed in layilin-KO cells.

Conclusion: We here demonstrated that layilin played a role in the maintenance of fragmented mitochondria in mitochondrial dynamics and that this function needed CDK1 and DRP1 activation. Our data unveiled a novel function for layilin, regulation of mitochondrial dynamics.