The emerging role of Never-in-Mitosis A – Related Kinases in the endothelium microbiology

Barrier function and Never-in-Mitosis A – Related Kinases

The endothelial permeability is affected by a plethora of cellular and environmental stimuli, and it is regulated by a meticulously organized molecular network, to safeguard homeostasis under a diverse variety of stresses. Several kinases have been identified to mediate–and potentiate-inflammatory responses, which in turn induce tissue dysfunction. An emerging body of evidence supports the involvement of Never-in-Mitosis A (NIMA) – Related Kinases – or NEKs – in endothelium-related disorders.

NEK1 in the blood brain barrier

NEK1 is involved in cell cycle, cilia formation, DNA-damage response, microtubule stability, and neural development regulation. Excess NEK1 catalytic activity leads to primary glia loss. NEK1 – deficient cells display defective G1/S and G2/M checkpoints and impaired DNA repair after ionizing radiation (Moniz, 2011). NEK1 – deficient mice demonstrated postnatal lethality due to cerebrovascular endothelial cell necroptosis (Wang, 2021).

NEK2 involvement in P53 regulation and endothelial permeability

NEK2 is closely related to the prototypic Aspergillus nidulans NIMA. It promotes the splitting of duplicated centrosomes via centriolar protein phosphorylation (Fry, 2002). NEK2-mediated P53 phosphorylation at Ser 315 reduces P53 stability (Choi, 2018). This tumor suppressor regulates the Ras-related C3 botulinum toxin substrate 1/ Ras homolog family member A balance in the endothelium and supports vascular integrity (Fig. 1) (Barabutis, 2015).

Bovine pulmonary artery endothelial cells (BPAEC)

NEK4 in endothelial hypoxia

NEK4 is involved in post-mitotic cell cilia, regulates the entry into replicative senescence, and participates in DNA damage responses. Gene expression analysis in human pulmonary artery endothelial cells revealed that hypoxic conditions affect NEK4 levels (Nguyen, 2012). NEK4 overexpression resulted to decreased levels of VE-Cadherin, and promoted lung cancer metastasis via epithelial-to-mesenchymal transition interference. Furthermore, NEK4 knockdown reduced tumor formation and metastasis (

NEK6 in lung cancer

NEK6 and NEK7 have 85 % sequence identity (Sun, 2020). NEK6 expression levels were increased in human non-small lung carcinoma lung tissues, as compared to paired non-tumor tissues, and were associated to metastatic progression (Cao, 2021). NCI-H1299 and NCI-H1975 lung cancer cells express high levels of NEK6, and specific inhibitors are being developed – and tested – against cancers (Li, 2015). NEK6 mRNA levels were associated with poor prognosis in pulmonary malignancies (Cao, 2021).

NEK7 in retinopathy and brain injury

NEK7 is an essential mediator of NLRP3 activation downstream of potassium efflux (He, 2016). Retinal endothelial cell NEK7 inhibition ameliorates high glucose induced-human endothelial dysfunction, a complication of diabetic retinopathy (He, 2016). Progressive endothelial eye disorders may lead to blindness. In Fuchs’ endothelial corneal dystrophy, corneal transplantation is the only therapeutic option; and the majority of Graves’ disease patients present with thyroid eye ophthalmopathy (Nanda

NEK9 in lung inflammatory disease and permeability

NEK9 activation phosphorylates NEK6 and NEK7 to modulate kinesin-like protein 11 and microtubule formation; and to ensure proper cytoskeletal and mitotic spindle arrangement (Fry, 2012). In lung cancers, co-expression of NEK9 and mutant p53 promoted cell proliferation via mitogen activated protein kinase 14 upregulation (Kurioka, 2014). LPS induced NEK9 expression in endothelial cells and in septic mice. Targeted suppression of that kinase alleviated LPS-induced barrier dysfunction (Barabutis

NEK10 and NEK11 in stress responses

NEK10 controls the G2/M checkpoint and phosphorylates P53 on tyrosine 327, to modulate p53-responsive genes in the context of growth, DNA replication, and stress response (Haider, 2020) (Table 1). This is important because P53 is a key regulator of barrier integrity, and mediates – at least in part – the protective activities of GHRH antagonists and heat shock protein 90 inhibitors in the endothelium (Barabutis, 2022). NEK10 regulates β-catenin turnover. A549 cells deficient for that kinase

Enzyme inhibitors in clinics

Enzyme-based therapeutics have been successfully applied in clinical trials. The β-Hydroxy β-methylglutaryl-CoA reductase inhibitors reduce ameliorate cardiovascular disease. Angiotensin-converting enzyme inhibitors manage hypertension and reduce mortality following myocardial infarction. Viral protease inhibitors are used to treat HIV infections. Elevated NEK expression levels have been associated with human disease (Table 1), and at least 2 NEKs modulate barrier function (Barabutis and

Future Directions

Many questions on the role of NEKs in endothelial function remain unanswered. Which is the exact role of those proteins in cytoskeletal protein modulation (e.g. VE-Cadherin, zonula occludens); transcellular/paracellular permeability; and inflammatory response in response to bacterial infection or injury? The potential interrelations of NEKs and unfolded protein response (UPR) in the endothelial context would be an intriguing topic of research. There is a positive regulation of P53 and UPR in

Conclusive remarks

The flawless transport of nutrients and gases through the endothelial semipermeable monolayers is crucial for tissue function and survival. Endothelial hyperpermeability is associated with acute lung injury, acute respiratory distress syndrome (ARDS) related or not to COVID-19, keratitis, BBB dysfunction, thyroid ophthalmopathy (Table 1). In our view, the potential beneficial effects of NEK inhibitors in experimental models of endothelial-related illness should be explored, since there is an

Funding

Nektarios Barabutis is supported by: a) The National Institute of Allergy and Infectious Diseases of the National Institutes of Health under Award Number R03AI176433; b) An Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under Award Number P20 GM103424-21. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

CRediT authorship contribution statement

Saikat Fakir: Writing – review & editing. Nektarios Barabutis: Writing – review & editing, Writing – original draft, Supervision, Project administration, Conceptualization.

Declaration of Competing Interest

The authors declare no conflict of interests