The role of the hCDC14B-HIPK2-MeCP2 axis in mitotic cell fate determination.

• Applicant: Professor Dr. Elmar Schiebel
• Subject Area: Cell Biology
• Term: since 2006
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 22423221

CDC14 is a conserved phosphatase that in the model organism budding yeast has an essential function in the regulation of mitotic exit, the transition from mitosis into G1. Human cells have three CDC14 paralogues of which only hCDC14A and hCDC14B are widely expressed. In the past we have analysed the functions of hCDC14A and hCDC14B and have identified substrates of these phosphatases. hCDC14A is associated with centrosomes and the actin cytoskeleton and we have shown functions in actin organisation and cilia length control. In contrast, hCDC14B associates with the nucleolus during interphase and binds to centrosomes and chromatin in mitosis. Recently, we have identified hCDC14B substrates through phospho-proteome analysis of hCDC14B overexpressing cells. The protein MeCP2 (Methyl CpG binding Protein 2) that binds to tri-methylated histone H3 where it functions as transcriptional repressor was identified as hCDC14B substrate.Analysis of untransformed human RPE1 cells with genomic deletion in hCDC14B revealed that cyclin B1 protein levels (and thereby CDK1-cyclin B1 activity) are increased in these cells, similar to published data from CDC14B KO mouse embryonic fibroblasts. Our data suggest that this increase in cyclin B1 has the consequence that cells with disturbances that affect the mitotic spindle stay longer in mitosis in comparison to hCDC14B wild type cells. Our preliminary data suggest that cyclin B1 is controlled by the antagonistic activities of hCDC14B and the kinase HIPK2 (Homeodomain Interacting Protein Kinase 2) on MeCP2S92. Phosphorylated MeCP2S92 then promotes, probably via translation control, enhanced accumulation of cyclin B1. This model is supported by numerous preliminary data and suggests a novel regulatory mechanism that controls progression through mitosis and cell fate decision (slippage into G1 versus mitotic cell death) in response to mitotic disturbances. Here we will test this model further. We will study how altered hCDC14B levels impact cell fate in response to mitotic disturbances, how this impacts cyclin B1 and finally we will test the notion that the phosphorylation status of MeCP2 as determined by HIPK2 and hCDC14B controls translation of cyclin B1 by an unknown mechanism. The second part is focused on the regulation of HIPK2 in response to mitotic stress, the consequences of HIPK2 modifications, whether the spindle assembly checkpoint regulates HIPK2 and how HIPK2 becomes stabilized under mitotic stress conditions. Together, this project will help us to understand how cells adjust cyclin B1 levels in response to mitotic disturbances and how this impacts cell fate decision. Since mitotic slippage into G1 is accompanied with the formation of tetraploid cells that are an intermediate state in neoplastic transformation, this proposal will help understanding the mechanistic principals of this deleterious step and how it can be prevented.

• DFG Programme: Research Grants