In previous years, several kinases, such as phosphoinositide 3-kinase (PI3K), mammalian target of rapamycin (mTOR), and extracellular-signal-regulated kinase (ERK), have been linked to important human diseases, although some kinase families remain neglected in terms of research, hiding their relevance to therapeutic approaches. Here, a review regarding the NEK family is presented, shedding light on important information related to NEKs and human diseases. NEKs are a large group of homologous kinases with related functions and structures that participate in several cellular processes such as the cell cycle, cell division, cilia formation, and the DNA damage response. The review of the literature points to the pivotal participation of NEKs in important human diseases, like different types of cancer, diabetes, ciliopathies and central nervous system related and inflammatory-related diseases. The different known regulatory molecular mechanisms specific to each NEK are also presented, relating to their involvement in different diseases. In addition, important information about NEKs remains to be elucidated and is highlighted in this review, showing the need for other studies and research regarding this kinase family. Therefore, the NEK family represents an important group of kinases with potential applications in the therapy of human diseases.

NIMA-related kinases, or NEKs, are a family of Ser/Thr protein kinases involved in cell cycle and mitosis, centrosome disjunction, primary cilia functions, and DNA damage responses among other biological functional contexts in vertebrate cells. In human cells, there are 11 members, termed NEK1 to 11, and the research has mainly focused on exploring the more predominant roles of NEKs in mitosis regulation and cell cycle. A possible important role of NEKs in DNA damage response (DDR) first emerged for NEK1, but recent studies for most NEKs showed participation in DDR. A detailed analysis of the protein interactions, phosphorylation events, and studies of functional aspects of NEKs from the literature led us to propose a more general role of NEKs in DDR. In this review, we express that NEK1 is an activator of ataxia telangiectasia and Rad3-related (ATR), and its activation results in cell cycle arrest, guaranteeing DNA repair while activating specific repair pathways such as homology repair (HR) and DNA double-strand break (DSB) repair. For NEK2, 6, 8, 9, and 11, we found a role downstream of ATR and ataxia telangiectasia mutated (ATM) that results in cell cycle arrest, but details of possible activated repair pathways are still being investigated. NEK4 shows a connection to the regulation of the nonhomologous end-joining (NHEJ) repair of DNA DSBs, through recruitment of DNA-PK to DNA damage foci. NEK5 interacts with topoisomerase IIβ, and its knockdown results in the accumulation of damaged DNA. NEK7 has a regulatory role in the detection of oxidative damage to telomeric DNA. Finally, NEK10 has recently been shown to phosphorylate p53 at Y327, promoting cell cycle arrest after exposure to DNA damaging agents. In summary, this review highlights important discoveries of the ever-growing involvement of NEK kinases in the DDR pathways. A better understanding of these roles may open new diagnostic possibilities or pharmaceutical interventions regarding the chemo-sensitizing inhibition of NEKs in various forms of cancer and other diseases.

Mitochondria provide energy for all cellular processes, including reactions associated with cell cycle progression, DNA damage repair, and cilia formation. Moreover, mitochondria participate in cell fate decisions between death and survival. Nek family members have already been implicated in DNA damage response, cilia formation, cell death, and cell cycle control. Here, we discuss the role of several Nek family members, namely Nek1, Nek4, Nek5, Nek6, and Nek10, which are not exclusively dedicated to cell cycle-related functions, in controlling mitochondrial functions. Specifically, we review the function of these Neks in mitochondrial respiration and dynamics, mtDNA maintenance, stress response, and cell death. Finally, we discuss the interplay of other cell cycle kinases in mitochondrial function and vice versa. Nek1, Nek5, and Nek6 are connected to the stress response, including ROS control, mtDNA repair, autophagy, and apoptosis. Nek4, in turn, seems to be related to mitochondrial dynamics, while Nek10 is involved with mitochondrial metabolism. Here, we propose that the participation of Neks in mitochondrial roles is a new functional axis for the Nek family.

The family of Nek kinases has 11 human members that are conserved in their kinase domains but diverse in their regulatory domains. Functionally, they can be associated with diverse aspects of cell cycle regulation, from mitosis and primary cilia function to centrosome disjunction in the G2 phase and checkpoints of the DNA damage response. However, novel functional contexts have emerged in recent years, including regulatory roles of Neks 1, 4, 5, and 10 in mitochondrial metabolic and morphological homeostasis. We recently generated, by CRISPR-Cas9 technology, a DU-145 prostate cancer cell line, with an NEK6 gene knockout. Here, we focus on a detailed characterization of changes in this cell line, in mitochondrial respiration function and morphology. DU-145 NEK6 knockout cells exhibited reduced mitochondrial respiration and a fragmented phenotype in electron microscopy, with reduced mitochondrial cristae numbers. Alterations in mitochondrial architecture and respiration were correlated with increased expression of anaerobic glycolytic proteins (HK2, PFKP, and LDHA) and decreased expression of PDH, an enzyme of aerobic glycolysis. Molecular analysis by Western blot revealed decreased levels of mitochondrial mass and biogenesis protein markers (TOM20, TFAM), without alterations in other markers such as VDAC1/3 or mtDNA copy number in the NEK6 knockout cells. Furthermore, the regulators of mitochondrial fusion/fission are altered in the knockout cells (decrease in the Long-OPA1:Short-OPA1 ratio and DRP1 total level), which is associated with an increase in endoplasmic reticulum–mitochondria contact at ≤20 nm observed in transmission electron microscopy (TEM) image analysis. Using analysis of TEM micrographs, we found an increase in the autophagic structures (autophagosome, amphisome, and autolysosome), with mitochondria as cargo in some structures, which was correlated with a decrease in LC3A/B and an increase in the BECLIN1 total level, and with an increase in acidic vesicles approximation, suggesting that reduction in TOM20 and TFAM without alterations in VDAC1/3 and mtDNA copy number might be related to mitochondrial degradation through autophagy. Together, our data suggest a new role for NEK6 in regulating mitochondrial homeostasis, where its loss alters mitochondrial morphology and respiration, and could be associated with an increase in the degradation of the dysfunctional mitochondria through autophagy.