Fang et al. Cell Div (2019) 14:4 https://doi.org/10.1186/s13008-019-0047-7 Cell Division RESEARCH Open Access HSP70 is required for the proper assembly of pericentriolar material and function of mitotic centrosomes Chieh‑Ting Fang1,2, Hsiao‑Hui Kuo2, Shao‑Chun Hsu2 and Ling‑Huei Yih2* Abstract Background: At the onset of mitosis, the centrosome expands and matures, acquiring enhanced activities for microtubule nucleation and assembly of a functional bipolar mitotic spindle. However, the mechanisms that regulate centrosome expansion and maturation are largely unknown. Previously, we demonstrated in an immortalized human cell line CGL2 and cancer cell line HeLa that the inducible form of heat shock protein 70 (HSP70) accumulates at the mitotic centrosome and is required for centrosome maturation and bipolar spindle assembly. Results: In this study, we further show that HSP70 accumulated at the spindle pole in a PLK1‑dependent manner. HSP70 colocalized with pericentrin (PCNT), CEP215 and γ‑tubulin at the spindle pole and was required for the 3D assembly of these three proteins, which supports mitotic centrosome function. Loss of HSP70 disrupted mitotic cen‑ trosome structure, reduced pericentriolar material recruitment and induced fragmentation of spindle poles. In addi‑ tion, HSP70 was necessary for the interaction between PCNT and CEP215 and also facilitated PLK1 accumulation and function at the spindle pole. Furthermore, we found that HSP70 chaperone activity is required for PCNT accumulation at the mitotic centrosome and assembly of mitotic spindles. Conclusion: Our current results demonstrate that HSP70 is required for the accurate assembly of the pericentriolar material and proper functioning of mitotic centrosomes. Keywords: HSP70, Mitotic centrosome, Pericentriolar material, Spindle pole Background Te centrosome is duplicated during S phase along with Te centrosome is a structurally complex and function- DNA replication, yielding two centrosomes that nucle- ally diverse organelle that regulates various cellular pro- ate extensive MT arrays and form the two poles of the cesses. It consists of a pair of barrel-shaped structures mitotic spindle [2]. Importantly, from late S phase to called centrioles and a surrounding protein complex, mitotic onset, the two fully duplicated centrosomes which is referred to as the pericentriolar material (PCM). exhibit enhanced recruitment of PCM components that Te PCM contains hundreds of proteins, including sign- are essential for MT nucleation, a process termed cen- aling molecules, cell cycle regulators and crucial micro- trosome maturation. In this process, PCM components tubule (MT)-nucleating factors. Te combined function accumulate at the existing centrosome and expand into of these proteins makes the centrosome the major MT- a greatly enlarged and intermingled matrix structure to organizing center (MTOC), which coordinates all MT- enhance MT nucleation capacity and promote the assem- related functions, including cell shape, cell polarity, bly of a functional bipolar spindle [3–5]. Inaccurate accu- mobility, intracellular trafcking and cell division [1]. mulation of PCM components at the centrosome results in a functionally compromised mitotic centrosome with *Correspondence: [email protected] multipolar or disorganized spindles that may further pro- 2 Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115, mote mitotic arrest, cell death and/or aneuploidy [6, 7]. Taiwan Full list of author information is available at the end of the article © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/ publi cdoma in/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Fang et al. Cell Div (2019) 14:4 Page 2 of 17 Previous studies using subdifraction resolution folding, oligomerization, trafcking, disaggregation, and microscopy and fuorescence recovery after photobleach- proteasomal or autophagic degradation. Among the wide ing have revealed that PCM components adopt either a variety of HSPs, HSP70 family members form a central concentric toroidal or an extending fber-like organi- hub of the chaperone networks that cooperatively utilize zation to form a thin layer of PCM at the interphase various chaperones and co-chaperones to regulate all centrosome; these structures then undergo extensive aspects of cellular proteostasis, especially protein qual- rearrangement, continuous replenishment, local trafck- ity control in certain organelles [24, 25]. HSP70 members ing, massive accumulation and expansion, and occupy in S. cerevisiae were proposed to control the oligomeric distinct subdomains within the dramatically enlarged state of Cin8 motor protein to regulate spindle length mitotic PCM matrix [3, 4, 8–13]. While the mecha- [26]. In mammalian cells, HSP70 mainly exists in consti- nisms that precisely regulate the behaviors of PCM tutive form (HSC70) and inducible form. Te inducible components are not clearly understood, several major HSP70 (thereafter HSP70) is phosphorylated by NEK6, contributors have been identifed. For example, Polo which targets HSP70 to the mitotic spindle where it like kinase 1 (PLK1) is a master mitotic kinase that is maintains kinetochore-MT stability and supports centro- known to phosphorylate multiple PCM substrates and some clustering [27, 28]. Additionally, HSP70 was also drive several steps of centrosome maturation [14–16]. shown to protect centrosome and spindle integrity when Additionally, pericentrin (PCNT) and CEP215 and their overexpressed, likely by preventing proteasomal degra- respective homologues in various model organism are dation of centrosomal proteins in the heat-shocked cells putative scafold proteins that are thought to physically [29, 30]. Tus, the importance of HSP70 in the mitotic interact at the maturing centrosome, providing a proper centrosome is well established, and some evidence sug- platform to recruit other PCMs [15, 17–19]. In the PCM gests that it may exert chaperone activities on centro- matrix, PCNT phosphorylation by PLK1 was shown some components to regulate centrosome maturation. to increase recruitment of MT nucleating factors, such We have previously demonstrated that HSP70 as NEDD1 and γ-tubulin, whose accumulation is also (encoded by genes HSPA1A and HSPA1B) localizes to PLK1-dependent [15, 17]. Notably, PLK1 activity persists the mitotic spindle poles and is required for maintenance throughout mitosis to ensure continuous replenishment of centrosome integrity, MT nucleation, mitotic spindle of PCM components, including PLK1 itself, suggesting assembly, mitotic progression, and cell viability [31]. In a highly dynamic and interdependent orchestration of this study, we further employed subdifraction resolution PCM components at the functional mitotic centrosome microscopy to examine the roles of HSP70 in the struc- [20, 21]. Despite these major advances in understanding ture and function of the mitotic centrosome. We found centrosome maturation, the highly organized regulatory that HSP70 cooperates with PLK1, PCNT, and CEP215 mechanisms governing the concentration and exchange to support their accumulation and proper 3D assembly, of these and other proteins at the mitotic centrosome and this action appears to be required for complete mat- are still largely unknown. Improper accumulation of uration of a fully functional mitotic centrosome. γ-tubulin has been implicated in abnormal spindle for- mation and human malignancies [22, 23]. Moreover, Results blocking PLK1 activity in the mitotic cells with already HSP70 accumulates at the spindle pole matured centrosomes reduces PCNT and γ-tubulin in a PLK1‑dependent manner and colocalizes with PCNT, accumulation [21], while mutant PLK1 with an altered CEP215 and γ‑tubulin exchange rate at the mitotic centrosome induces mitotic Based on our previous study, which used immunofuo- arrest [20]. Mutant PCNT that cannot be phosphoryl- rescence staining to reveal that HSP70 localizes to the ated by PLK1 fails to recruit multiple PCM components, spindle poles during mitosis [31], we frst investigated including PLK1 itself [15], while mutations that abol- how the localization of HSP70 at the spindle pole is reg- ish interaction between PCNT and CEP215 disrupt the ulated. Phosphorylation of HSP70 at various residues recruitment of themselves and γ-tubulin, inducing the has been shown to regulate its function [27, 32, 33], so formation of defective mitotic centrosomes and spindles we screened a series of kinase inhibitors to test whether [17]. Together, these data imply that delicate proteostatic they may afect the accumulation of HSP70 at the spin- control of PCM components is important for deter- dle pole. Te PLK inhibitor III (an inhibitor of PLK mem- mining the proper function of a fully matured mitotic bers) and BI2536 (an inhibitor of PLK1 [34]) dramatically centrosome. reduced the intensity of HSP70 at the spindle poles Molecular chaperones, such as heat shock proteins (Fig. 1A, B). Tis result is consistent with previous stud- (HSPs), are major orchestrators of the cellular proteo-