Haspin Kinase Research Articles

Structure–activity relationship study of acridine analogs as haspin and DYRK2 kinase inhibitors

Haspin is a serine/threonine kinase required for completion of normal mitosis that is highly expressed during cell proliferation, including in a number of neoplasms. Consequently, it has emerged as a potential therapeutic target in oncology. A high throughput screen of approximately 140,000 compounds identified an acridine analog as a potent haspin kinase inhibitor. Profiling against a panel of 270 kinases revealed that the compound also exhibited potent inhibitory activity for DYRK2, another serine/threonine kinase. An optimization study of the acridine series revealed that the structure–activity relationship (SAR) of the acridine series for haspin and DYRK2 inhibition had many similarities. However, several structural differences were noted that allowed generation of a potent haspin kinase inhibitor (33, IC50 <60nM) with 180-fold selectivity over DYRK2. In addition, a moderately potent DYRK2 inhibitor (41, IC50 <400nM) with a 5.4-fold selectivity over haspin was also identified.

Crystal structure of the catalytic domain of Haspin, an atypical kinase implicated in chromatin organization

Haspin, a nuclear and chromosome-associated serine/threonine (S/T) kinase, is responsible for mitotic phosphorylation of Thr-3 of histone H3. Haspin bears recognizable similarity to the eukaryotic protein kinase (ePK) fold, but its sequence is highly divergent and there is therefore considerable interest in its structural organization. We report the 2.15-A crystal structure of the kinase domain of human Haspin. The ePK fold of Haspin contains an array of insertions and deletions. The structure illustrates how Haspin escapes the classical activation scheme of most other kinases. The alphaC helix, which bears a conserved glutamate that is essential for catalysis, adopts its final active conformation within the small lobe of the kinase. It is sandwiched between an alpha-helical insertion that precedes the kinase domain, and the activation segment, which adopts an unprecedented conformation. The activation segment, which does not contain phosphorylatable residues, packs against an unusually structured alphaEF helix. Significantly extruded from the core of the fold, it forms an extensive plateau, hosting several residues implicated in substrate binding. Overall, the structure of the Haspin kinase domain reveals an active conformation that is poised for substrate recognition and phosphorylation in the absence of external regulators.

Chromatin remodeling during mitosis: a structure-based code?

Histone modifications have been associated with particular states of transcriptional activity and are thought to serve as an "information code". However, this principle does not apply to histone phosphorylation, which can be detected in two, seemingly contrasting situations, i.e., in a transcriptionally hyperactive state following growth factor stimulation and in transcriptionally paused mitotic chromosomes. There are several indications that mitotic phosphorylation of histone H3 at serine-10 by the Aurora B kinase and trimethylation at lysine-9 by the methyl transferase Suvar3,9 operate as a "binary switch", which determines recruitment or eviction of heterochromatin-specific proteins from pericentromeric repeats. Moreover, threonine-3 phosphorylation of histone H3 by the newly identified haspin kinase seems to promote chromatid cohesion during mitosis. We discuss here emerging information and new ideas suggesting that these modifications, in combination to upstream and downstream marks, constitute a system of intrinsic folding determinants that facilitate chromatin condensation and confer topological specificity to mitotic chromosomes.

Centromeric Aurora-B Activation Requires TD-60, Microtubules, and Substrate Priming Phosphorylation

The chromosome passenger complex (CPC) controls chromosome congression, kinetochore-microtubule attachments, and spindle checkpoint signaling during mitosis. Aurora-B kinase is the catalytic subunit of the CPC. To understand how a single kinase can regulate such diverse events, we have investigated the activation of Aurora-B and describe two distinct activation mechanisms. First, Aurora-B activation in vitro requires two cofactors, telophase disc-60kD (TD-60) and microtubules. TD-60 is critical to localize both the CPC and Haspin kinase activity to centromeres and thus regulates Aurora-B at several levels. Second, Aurora-B substrates can inhibit kinase activation, and this is relieved by phosphorylation of these substrates by the centromeric kinases Plk1 and Haspin. These regulatory mechanisms suggest models for phosphorylation by Aurora-B of centromeric substrates at unaligned chromosomes and merotelic attachments.

The Haspin gene: location in an intron of the Integrin αE gene, associated transcription of an Integrin αE-derived RNA and expression in diploid as well as haploid cells

Haspin is a serine/threonine kinase, recently identified in mice, that is thought to regulate cell cycle and differentiation of haploid germ cells. Here, the haspin gene is identified within an intron of the integrin αE gene. Transcription occurs from a bi-directional CpG island-associated promoter that also generates an alternatively spliced integrin αE derived RNA. Remarkably, the human and murine haspin genes lack introns, and have features of retroposons. The human haspin cDNA reveals that the human and murine proteins are 83% identical in the C-terminal kinase domain, but only 53% identical in the N-terminal region. The haspin kinase domain has structural features that distinguish it from previously characterized proteins and suggest that haspin is a member of a new family of protein kinases. Although formerly thought to be expressed selectively in the testes, haspin is also transcribed at lower levels in thymus, bone marrow, fetal liver and other fetal tissues, and in all proliferating cell lines tested. Thus haspin is likely to be important in regulation of diploid as well as haploid cell differentiation in a variety of tissues.