Abstract 1647: Plk4 phosphorylates the distal tip complex to promote centriole growth
Authors: Amoiroglou Anastasia , Ryniawec John M. , Buster Daniel W. , Rogers Gregory C. 
Published: March 2024

Abstract
The centrosome is the major microtubule-organizing center of the cell with a key role in forming the mitotic spindle. The centrosome consists of two core duplicating elements, the centrioles, surrounded by pericentriolar material, a cloud of proteins that nucleates microtubules. Centrioles are barrel-like structures composed of microtubule bundles and are essential to maintain centrosome number. Therefore, centriole duplication and growth are tightly regulated to ensure proper centrosome number throughout the cell cycle. Alterations in centrosome number lead to an abnormally shaped mitotic spindle that often mis-segregate chromosomes, thereby causing chromosomal instability, a hallmark of cancer. Defects in centriole growth, such as over-elongation, can increase centrosome numbers (known as ‘centriole amplification’, an overproduction of centrioles frequently observed in cancer cells). For example, over-elongation of the centriolar barrel can cause multiple ectopic daughter centrioles to assemble or simply fragment, producing multiple smaller (but functional) centrioles. Thus, understanding how centrioles grow and define length is a major question in the field. Centrioles elongate at their distal ends and, in Drosophila, elongation is regulated by a group of proteins, Cep97, CP110 and Klp10A. Elongation is negatively regulated by Cep97 and CP110 which cap centrioles at their distal end to maintain centriole length, by counteracting the microtubule depolymerizing kinesin, Klp10A. Recently, we identified a new centriole regulator, Cep104, that also localizes to the centriole distal tip. We discovered that Cep104 promotes centriole elongation through its microtubule-binding TOG domain. Additionally, Cep104 localization to the centriole distal ends is dependent on Cep97. Furthermore, Cep97, CP110, Cep104 and Klp10A form a complex and we have mapped their sites of interaction. Collectively, we refer to this as the Distal Tip Complex (DTC). Although the DTC is first recruited to new daughter centrioles during G1/S-phase, the majority of centriole elongation occurs during mitosis. Here, we explore the mechanisms that regulate the DTC to promote centriole growth during mitosis. We hypothesize that Polo-like kinase 4 (Plk4), the master regulator of centriole duplication, phosphorylates and inhibits the DTC to promote elongation of nascent centrioles. Notably, we found that centrioles are longer in cells overexpressing Plk4. Using tandem mass spectrometry, we identified multiple sites that Plk4 phosphorylates on each DTC protein. Analysis of DTC phosphomutants revealed that the phosphorylation state of Klp10A, Cep97 and CP110 affect centriole number. We are currently investigating how Plk4 phosphorylation regulates the activities of these conserved centriole length factors.
Citation Format: Anastasia Amoiroglou, John M. Ryniawec, Daniel W. Buster, Gregory C. Rogers. Plk4 phosphorylates the distal tip complex to promote centriole growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1647.