Structure, Roles and Inhibitors of a Mitotic Protein Kinase Haspin

Germ cell-specific gene 2 accelerates cell cycle in epithelial ovarian cancer by inhibiting GSK3α-p27 cascade

Epithelial ovarian cancer (EOC) is one of the most common malignant gynecological tumors with rapid growth potential and poor prognosis, however, the molecular mechanism underlying its outgrowth remained elusive. Germ cell-specific gene 2 (GSG2) was previously reported to be highly expressed in ovarian cancer and was essential for the growth of EOC. In this study, GSG2-knockdown cells and GSG2-overexpress cells were established through lentivirus-mediated transfection with Human ovarian cancer cells HO8910 and SKOV3. Knockdown of GSG2 inhibited cell proliferation and induced G2/M phase arrest in EOC. Interestingly, the expression of p27, a well-known regulator of the cell cycle showed a most significant increase after GSG2 knockdown. Further phosphorylation-protein array demonstrated the phosphorylation of GSK3αSer21 decreased in GSG2-knockdown cells to the most extent. Notably, inhibiting GSK3α activity effectively rescued GSG2 knockdown's suppression on cell cycle as well as p27 expression in EOC. Our study substantiates that GSG2 is able to phosphorylate GSK3α at Ser21 and then leads to the reduction of p27 expression, resulting in cell cycle acceleration and cell proliferation promotion. Thus, GSG2 may have the potential to become a promising target in EOC.

Synthesis and evaluation of novel N1-acylated 5-(4-pyridinyl)indazole derivatives as potent and selective haspin inhibitors

Protein kinase dysregulation was strongly linked to cancer pathogenesis. Moreover, histone alterations were found to be among the most important post-translational modifications that could contribute to cancer growth and development. In this context, haspin, an atypical serine/threonine kinase, phosphorylates histone H3 at threonine-3 and is notably overexpressed in various common cancer types. Herein, we report novel 5-(4-pyridinyl)indazole derivatives as potent and selective haspin inhibitors. Amide coupling at N1 of the indazole ring with m-hydroxyphenyl acetic acid yielded compound 21 with an IC50 value of 78 nM against haspin. This compound showed a meaningful selectivity over 15 of the most common off-targets, including Clk 1-3 and Dyrk1A, 1B, and 2. The most potent haspin inhibitors 5 and 21 effectively inhibited the growth of the NCI-60 cancer cell lines, further emphasizing the success of our scaffold as a new selective lead for the development of anti-cancer therapeutic agents.

Haspin participates in AURKB recruitment to centromeres and contributes to chromosome congression in male mouse meiosis

Chromosome segregation requires that centromeres properly attach to spindle microtubules. This essential step regulates the accuracy of cell division and therefore must be precisely regulated. One of the main centromeric regulatory signaling pathways is the Haspin-H3T3ph-chromosomal passenger complex (CPC) cascade, which is responsible for the recruitment of the CPC to the centromeres. In mitosis, Haspin kinase phosphorylates histone H3 at threonine 3 (H3T3ph), an essential epigenetic mark that recruits the CPC, whose catalytic component is Aurora B kinase. However, the centromeric Haspin-H3T3ph-CPC pathway remains largely uncharacterized in mammalian male meiosis. We have analyzed Haspin functions by either its chemical inhibition in cultured spermatocytes using LDN-192960, or the ablation of Haspin gene in Haspin-/-. Our studies suggest that Haspin kinase activity is required for proper chromosome congression during both meiotic divisions and for the recruitment of Aurora B and kinesin MCAK to meiotic centromeres. However, the absence of H3T3ph histone mark does not alter Borealin and SGO2 centromeric localization. These results add new and relevant information regarding the regulation of the Haspin-H3T3ph-CPC pathway and centromere function during meiosis.

Loss of haspin suppresses cancer cell proliferation by interfering with cell cycle progression at multiple stages

Our recent studies have shown that haspin, a protein kinase imperative for mitosis, is engaged in the interphase progression of HeLa and U2OS cancer cells. In this investigation, we employed the Fucci reporter system and time-lapse imaging to examine the impact of haspin gene silencing on cell cycle progressions at a single-cell level. We found that the loss of haspin induced multiple cell cycle defects. Specifically, the S/G2 duration was greatly prolonged by haspin gene depletion or inhibition in synchronous HeLa cells. Haspin gene depletion in asynchronous HeLa and U2OS cells led to a similarly protracted S/G2 phase, followed by mitotic cell death or postmitotic G1 arrest. In addition, haspin deficiency resulted in robust induction of the p21^CIP1/WAF1 checkpoint protein, a target of the p53 activation. Also, co-depleting haspin with either p21 or p53 could rescue U2OS cells from postmitotic G1 arrest and partially restore their proliferation. These results substantiate the haspin's capacity to regulate interphase and mitotic progression, offering a broader antiproliferative potential of haspin loss in cancer cells.

Exploring the thermodynamic, kinetic and inhibitory mechanisms of 5-iTU targeting mitotic kinase haspin by integrated molecular dynamics

As a human mitotic kinase, haspin is considered as a promising target for various diseases including cancers. However, no inhibitors targeting haspin have entered clinical trials presently. 5-iTU (5-iodotubercidin) is a useful and classical chemical probe for the investigation of haspin activity, but its inhibitory mechanism remains unclear. In this study, integrated molecular dynamics (MD) of conventional MD, extended adaptive biasing force (eABF), random acceleration MD and well-tempered metadynamics were applied to investigate the thermodynamic and kinetic features of 5-iTU and three derivatives targeting haspin. To emphasize the importance of gatekeeper Phe605, two haspin mutants (F605Y and F605T) were also built. The results showed that the binding affinity of 5-iTU and haspin was highest in all wild type (WT) systems, relying on the strong halogen aromatic π interaction between 5-iTU and gatekeeper Phe605. Gatekeeper mutations, because of damage to this interaction, led to the rearrangement of water distributions at the binding site and the decrease of 5-iTU residence times. Additionally, compared with the smaller 5-fTU, 5-iTU dissociated from WT haspin with more difficulty through distinct unbinding pathways. These findings will provide crucial guidance for the design and development of novel haspin inhibitors and the rational modification of existing inhibitors.

CRISPR/Cas9 screening identifies a kinetochore-microtubule dependent mechanism for Aurora-A inhibitor resistance in breast cancer

Background

Overexpression of Aurora‐A (AURKA) is a feature of breast cancer and associates with adverse prognosis. The selective Aurora‐A inhibitor alisertib (MLN8237) has recently demonstrated promising antitumor responses as a single agent in various cancer types but its phase III clinical trial was reported as a failure since MLN8237 did not show an apparent effect in prolonging the survival of patients. Thus, identification of potential targets that could enhance the activity of MLN8237 would provide a rationale for drug combination to achieve better therapeutic outcome.

Methods

Here, we conducted a systematic synthetic lethality CRISPR/Cas9 screening of 507 kinases using MLN8237 in breast cancer cells and identified a number of targetable kinases that displayed synthetic lethality interactions with MLN8237. Then, we performed competitive growth assays, colony formation assays, cell viability assays, apoptosis assays, and xenograft murine model to evaluate the synergistic therapeutic effects of Haspin (GSG2) depletion or inhibition with MLN8237. For mechanistic studies, immunofluorescence was used to detect the state of microtubules and the localization of Aurora‐B and mitotic centromere‐associated kinesin (MCAK).

Results

Among the hits, we observed that Haspin depletion or inhibition marginally inhibited breast cancer cell growth but could substantially enhance the killing effects of MLN8237. Mechanistic studies showed that co‐treatment with Aurora‐A and Haspin inhibitors abolished the recruitment of Aurora‐B and mitotic centromere‐associated kinesin (MCAK) to centromeres which were associated with excessive microtubule depolymerization, kinetochore‐microtubule (KT‐MT) attachment failure, and severe mitotic catastrophe. We further showed that the combination of MLN8237 and the Haspin inhibitor CHR‐6494 synergistically reduced breast cancer cell viability and significantly inhibited both in vitro and in vivo tumor growth.

Conclusions

These findings establish Haspin as a synthetic lethal target and demonstrate CHR‐6494 as a potential combinational drug for promoting the therapeutic effects of MLN8237 on breast cancer.

GSG2 (Haspin) promotes development and progression of bladder cancer through targeting KIF15 (Kinase-12)

Bladder cancer is the most commonly diagnosed malignant tumor in urological system worldwide. The relationship between GSG2 and bladder cancer has not been demonstrated and remains unclear. In this study, it was demonstrated that GSG2 was up-regulated in bladder cancer tissues compared with the normal tissues and its high expression was correlated with more advanced malignant grade and lower survival rate. Further investigations indicated that the overexpression/knockdown of GSG2 could promote/inhibit proliferation, colony formation and migration of bladder cancer cells, while inhibiting/promoting cell apoptosis. Moreover, knockdown of GSG2 could also suppress tumorigenicity of bladder cancer cells in vivo. RNA-sequencing followed by Ingenuity pathway analysis (IPA) was performed for exploring downstream of GSG2 and identified KIF15 as the potential target. Furthermore, our study revealed that knockdown of KIF15 could inhibit development of bladder cancer in vitro, and alleviate the GSG2 overexpression induced promotion of bladder cancer. In conclusion, our study showed, as the first time, GSG2 as a prognostic indicator and tumor promotor for bladder cancer, whose function was carried out probably through the regulation of KIF15.

Genome-wide CRISPR screen uncovers a synergistic effect of combining Haspin and Aurora kinase B inhibition

Aurora kinases are a family of serine/threonine kinases vital for cell division. Because of the overexpression of Aurora kinases in a broad range of cancers and their important roles in mitosis, inhibitors targeting Aurora kinases have attracted attention in cancer therapy. VX-680 is an effective pan-Aurora kinase inhibitor; however, its clinical efficacy was not satisfying. In this study, we performed CRISPR/Cas9 screens to identify genes whose depletion shows synthetic lethality with VX-680. The top hit from these screens was GSG2 (also known as Haspin), a serine/threonine kinase that phosphorylates histone H3 at Thr-3 during mitosis. Moreover, both Haspin knockout and Haspin inhibitor-treated HCT116 cells were hypersensitive to VX-680. Furthermore, we showed that the synthetic lethal interaction between Haspin depletion and VX-680 was mediated by the inhibition of Haspin with Aurora kinase B (AURKB), but not with Aurora kinase A (AURKA). Strikingly, combined inhibition of Haspin and AURKB had a better efficacy than single-agent treatment in both head and neck squamous cell carcinoma and non-small cell lung cancer. Taken together, our findings have uncovered a synthetic lethal interaction between AURKB and Haspin, which provides a strong rationale for this combination therapy for cancer patients.

Knockdown of GSG2 inhibits prostate cancer progression in vitro and in vivo

Prostate cancer (PCa) is the second leading cause of cancer related death among men worldwide. The present study aimed to investigate the role of germ cell-specific gene 2 protein (GSG2), also termed histone H3 phosphorylated by GSG2 at threonine 3, in the development and progression of PCa. GSG2 expression levels in PCa tissues and para carcinoma tissues was detected by immunohistochemistry. The GSG2 knockdown cell model was constructed by lentivirus infec tion, and the knockdown efficiency was verified by qPCR and WB. In addition, the effects of shGSG2 on cell proliferation, colony formation and apoptosis were evaluated by Celigo cell counting assay, Giemsa staining and flow cytometry, respec tively. Tumor development in nude mice was also detected. GSG2 expression was upregulated in PCa tissues and human PCa cell lines PC 3 and DU 145. High expression of GSG2 in tumor samples was associated with progressed tumors. GSG2 knockdown suppressed cell proliferation and colony forma tion, but promoted apoptosis, which was also verified in vivo. The results of the present study revealed that GSG2 upregula tion was associated with PCa progression; GSG2 knockdown inhibited cell proliferation and colony formation and induced apoptosis, and may therefore serve as a potential therapeutic target for PCa therapy.

Haspin inhibition delays cell cycle progression through interphase in cancer cells

Haspin (Haploid Germ Cell-Specific Nuclear Protein Kinase) is a serine/threonine kinase pertinent to normal mitosis progression and mitotic phosphorylation of histone H3 at threonine 3 in mammalian cells. Different classes of small molecule inhibitors of haspin have been developed and utilized to investigate its mitotic functions. We report herein that applying haspin inhibitor CHR-6494 or 5-ITu at the G1/S boundary could delay mitotic entry in synchronized HeLa and U2OS cells, respectively, following an extended G2 or the S phase. Moreover, late application of haspin inhibitors at S/G2 boundary is sufficient to delay mitotic onset in both cell lines, thereby, indicating a direct effect of haspin on G2/M transition. A prolonged interphase duration is also observed with knockdown of haspin expression in synchronized and asynchronous cells. These results suggest that haspin can regulate cell cycle progression at multiple stages at both interphase and mitosis.