Human NIMA-related kinase 6 is one of the Fe65 WW domain binding proteins

NIMA-related kinase-6 (NEK6) as an executable target in cancer

Cancer is a disease that develops when cells begin to divide uncontrollably and spreads to other parts of the body. Proliferation and invasion of cancerous cells are generally known to be influenced by cell cycle-related proteins in human malignancies. Therefore, in this review, we have emphasized on the serine/threonine kinase named NEK6. NEK6 is been deliberated to play a critical role in mitosis progression that includes mitotic spindle formation, metaphase to anaphase transition, and centrosome separation. Moreover, it has a mechanistic role in DNA repair and can cause apoptosis when inhibited. Past studies have connected NEK6 protein expression to cancer cell senescence. Besides, there are reports relating NEK6 to a range of malignancies including breast, lung, ovarian, prostate, kidney, liver, and others. Given its significance, this review attempts to describe the structural and functional aspects of NEK6 in various cellular processes, as well as how it is linked to different forms of cancer. Lastly, we have accentuated, on some of the plausible inhibitors that have been explored against NEK6 overexpression.

Hydrogen Sulfide: Recent Progression and Perspectives for the Treatment of Diabetic Nephropathy

Diabetic kidney disease develops in approximately 40% of diabetic patients and is a major cause of chronic kidney diseases (CKD) and end stage kidney disease (ESKD) worldwide. Hydrogen sulfide (H₂S), the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO), is synthesized in nearly all organs, including the kidney. Though studies on H₂S regulation of renal physiology and pathophysiology are still in its infancy, emerging evidence shows that H₂S production by renal cells is reduced under disease states and H₂S donors ameliorate kidney injury. Specifically, aberrant H₂S level is implicated in various renal pathological conditions including diabetic nephropathy. This review presents the roles of H₂S in diabetic renal disease and the underlying mechanisms for the protective effects of H₂S against diabetic renal damage. H₂S may serve as fundamental strategies to treat diabetic kidney disease. These H₂S treatment modalities include precursors for H₂S synthesis, H₂S donors, and natural plant-derived compounds. Despite accumulating evidence from experimental studies suggests the potential role of the H₂S signaling pathway in the treatment of diabetic nephropathy, these results need further clinical translation. Expanding understanding of H₂S in the kidney may be vital to translate H₂S to be a novel therapy for diabetic renal disease.

The Role of Hydrogen Sulfide in Renal System

Hydrogen sulfide has gained recognition as the third gaseous signaling molecule after nitric oxide and carbon monoxide. This review surveys the emerging role of H2S in mammalian renal system, with emphasis on both renal physiology and diseases. H2S is produced redundantly by four pathways in kidney, indicating the abundance of this gaseous molecule in the organ. In physiological conditions, H2S was found to regulate the excretory function of the kidney possibly by the inhibitory effect on sodium transporters on renal tubular cells. Likewise, it also influences the release of renin from juxtaglomerular cells and thereby modulates blood pressure. A possible role of H2S as an oxygen sensor has also been discussed, especially at renal medulla. Alternation of H2S level has been implicated in various pathological conditions such as renal ischemia/reperfusion, obstructive nephropathy, diabetic nephropathy, and hypertensive nephropathy. Moreover, H2S donors exhibit broad beneficial effects in renal diseases although a few conflicts need to be resolved. Further research reveals that multiple mechanisms are underlying the protective effects of H2S, including anti-inflammation, anti-oxidation, and anti-apoptosis. In the review, several research directions are also proposed including the role of mitochondrial H2S in renal diseases, H2S delivery to kidney by targeting D-amino acid oxidase/3-mercaptopyruvate sulfurtransferase (DAO/3-MST) pathway, effect of drug-like H2S donors in kidney diseases and understanding the molecular mechanism of H2S. The completion of the studies in these directions will not only improves our understanding of renal H2S functions but may also be critical to translate H2S to be a new therapy for renal diseases.

FE65: Roles beyond amyloid precursor protein processing

FE65 is a brain-enriched, developmentally regulated adaptor protein that was first identified as a binding partner of amyloid precursor protein (APP), an important molecule in Alzheimer's disease. FE65 possesses three protein interaction domains, including an N-terminal WW domain and two C-terminal phosphotyrosine-binding (PTB) domains. It is capable of mediating the assembly of multimolecular complexes. Although initial work reveals its roles in APP processing and gene transactivation, increasing evidence suggests that FE65 participates in more diverse biological processes than originally anticipated. This article discusses the role of FE65 in signal transduction during cell stress and protein turnover through the ubiquitin-proteasome system and in various neuronal processes, including neurogenesis, neuronal migration and positioning, neurite outgrowth, synapse formation and synaptic plasticity, learning, and memory.

“Stop Ne(c)king around”: How interactomics contributes to functionally characterize Nek family kinases

Aside from Polo and Aurora, a third but less studied kinase family involved in mitosis regulation is the never in mitosis-gene A (NIMA)-related kinases (Neks). The founding member of this family is the sole member NIMA of Aspergillus nidulans, which is crucial for the initiation of mitosis in that organism. All 11 human Neks have been functionally assigned to one of the three core functions established for this family in mammals: (1) centrioles/mitosis; (2) primary ciliary function/ciliopathies; and (3) DNA damage response (DDR). Recent findings, especially on Nek 1 and 8, showed however, that several Neks participate in parallel in at least two of these contexts: primary ciliary function and DDR. In the core section of this in-depth review, we report the current detailed functional knowledge on each of the 11 Neks. In the discussion, we return to the cross-connections among Neks and point out how our and other groups’ functional and interactomics studies revealed that most Neks interact with protein partners associated with two if not all three of the functional contexts. We then raise the hypothesis that Neks may be the connecting regulatory elements that allow the cell to fine tune and synchronize the cellular events associated with these three core functions. The new and exciting findings on the Nek family open new perspectives and should allow the Neks to finally claim the attention they deserve in the field of kinases and cell cycle biology.

Degradation of mutant huntingtin via the ubiquitin/proteasome system is modulated by FE65

An unstable expansion of the polyglutamine repeat within exon 1 of the protein Htt (huntingtin) causes HD (Huntington's disease). Mounting evidence shows that accumulation of N-terminal mutant Htt fragments is the source of disruption of normal cellular processes which ultimately leads to neuronal cell death. Understanding the degradation mechanism of mutant Htt and improving its clearance has emerged as a new direction in developing therapeutic approaches to treat HD. In the present study we show that the brain-enriched adaptor protein FE65 is a novel interacting partner of Htt. The binding is mediated through WW-polyproline interaction and is dependent on the length of the polyglutamine tract. Interestingly, a reduction in mutant Htt protein level was observed in FE65-knockdown cells, and the process requires the UPS (ubiquitin/proteasome system). Moreover, the ubiquitination level of mutant Htt was found to be enhanced when FE65 is knocked down. Immunofluroescence staining revealed that FE65 associates with mutant Htt aggregates. Additionally, we demonstrated that overexpression of FE65 increases mutant Htt-induced cell death both in vitro and in vivo. These results suggest that FE65 facilitates the accumulation of mutant Htt in cells by preventing its degradation via the UPS, and thereby enhances the toxicity of mutant Htt.

The amyloid precursor protein intracellular domain-fe65 multiprotein complexes: a challenge to the amyloid hypothesis for Alzheimer's disease?

Since its proposal in 1994, the amyloid cascade hypothesis has prevailed as the mainstream research subject on the molecular mechanisms leading to the Alzheimer's disease (AD). Most of the field had been historically based on the role of the different forms of aggregation of β-amyloid peptide (Aβ). However, a soluble intracellular fragment termed amyloid precursor protein (APP) intracellular domain (AICD) is produced in conjunction with Aβ fragments. This peptide had been shown to be highly toxic in both culture neurons and transgenic mice models. With the advent of this new toxic fragment, the centerpiece for the ethiology of the disease may be changed. This paper discusses the potential role of multiprotein complexes between the AICD and its adapter protein Fe65 and how this could be a potentially important new agent in the neurodegeneration observed in the AD.

Human Nek6 is a monomeric mostly globular kinase with an unfolded short N-terminal domain

BACKGROUND

The NIMA-related kinases (Neks) are widespread among eukaryotes. In mammalians they represent an evolutionarily conserved family of 11 serine/threonine kinases, with 40-45% amino acid sequence identity to the Aspergillus nidulans mitotic regulator NIMA within their catalytic domains. Neks have cell cycle-related functions and were recently described as related to pathologies, particularly cancer, consisting in potential chemotherapeutic targets. Human Nek6, -7 and -9 are involved in the control of mitotic spindle formation, acting together in a mitotic kinase cascade, but their mechanism of regulation remain elusive.

RESULTS

In this study we performed a biophysical and structural characterization of human Nek6 with the aim of obtaining its low resolution and homology models. SAXS experiments showed that hNek6 is a monomer of a mostly globular, though slightly elongated shape. Comparative molecular modeling together with disorder prediction analysis also revealed a flexible disordered N-terminal domain for hNek6, which we found to be important to mediate interactions with diverse partners. SEC-MALS experiments showed that hNek6 conformation is dependent on its activation/phosphorylation status, a higher phosphorylation degree corresponding to a bigger Stokes radius. Circular dichroism spectroscopy confirmed our in silico predictions of secondary structure content and thermal stability shift assays revealed a slightly higher stability of wild-type hNek6 compared to the activation loop mutant hNek6(S206A).

CONCLUSIONS

Our data present the first low resolution 3D structure of hNek6 protein in solution. SAXS, comparative modeling and SEC-MALS analysis revealed that hNek6 is a monomeric kinase of slightly elongated shape and a short unfolded N-terminal domain.

Role of NEK6 in tumor promoter-induced transformation in JB6 C141 mouse skin epidermal cells

NEK6 (NIMA-related kinase 6) is a homologue of the Aspergillus nidulans protein NIMA (never in mitosis, gene A). We demonstrate that overexpression of NEK6 induces anchorage-independent transformation of JB6 Cl41 mouse epidermal cells. Tissue arrays and Western immunoblot analysis show that NEK6 is overexpressed in malignant tissues and several cancer cell lines. Our data also show that NEK6 interacts with STAT3, an oncogenic transcription factor, and phosphorylates STAT3 on Ser(727), which is important for transcriptional activation. Additional studies using NEK6 mutants suggested that the phosphorylation on both Ser(206) and Thr(210) of NEK6 is critical for STAT3 phosphorylation and anchorage-independent transformation of mouse epidermal cells. Notably, knockdown of NEK6 decreased colony formation and STAT3 Ser(727) phosphorylation. Based on our findings, the most likely mechanism that can account for this biological effect involves the activation of STAT3 through the phosphorylation on Ser(727). Because of the critical role that STAT3 plays in mediating oncogenesis, the stimulatory effects of NEK6 on STAT3 and cell transformation suggest that this family of serine/threonine kinases might represent a novel chemotherapeutic target.

Ubiquitylation of Fe65 adaptor protein by neuronal precursor cell expressed developmentally down regulated 4-2 (Nedd4-2) via the WW domain interaction with Fe65

Fe65 has been characterized as an adaptor protein, originally identified as an expressed sequence tag (EST) corresponding to an mRNA expressed at high levels in the rat brain. It contains one WW domain and two phosphotyrosine interaction/phosphotyrosine binding domains (PID1/PID2). As the neuronal precursor cell expressed developmentally down regulated 4-2 (Nedd4-2) has a putative WW domain binding motif ((72)PPLP(75)) in the N-terminal domain, we hypothesized that Fe65 associates with Nedd4-2 through a WW domain interaction, which has the characteristics of E3 ubiquitin-protein ligase. In this paper, we present evidence for the interaction between Fe65 WW domain and Nedd4-2 through its specific motif, using a pull down approach and co-immunoprecipitation. Additionally, the co-localization of Fe65 and Nedd4-2 were observed via confocal microscopy. Co-localization of Fe65 and Nedd4-2 was disrupted by either the mutation of Fe65 WW domain or its putative binding motif of Nedd4-2. When the ubiquitin assay was performed, the interaction of Nedd4-2 (wt) with Fe65 is required for the cell apoptosis and the ubiquitylation of Fe65. We also observed that the ubiquitylation of Fe65 (wt) was augmented depending on Nedd4-2 expression levels, whereas the Fe65 WW domain mutant (W243KP245K) or the Nedd4-2 AL mutant ((72)PPLP(75) was changed to (72)APLA(75)) was under-ubiquitinated significantly. Thus, our observations implicated that the protein-protein interaction between the WW domain of Fe65 and the putative binding motif of Nedd4-2 down-regulates Fe65 protein stability and subcellular localization through its ubiquitylation, to contribute cell apoptosis.

The amyloid precursor protein intracellular domain (AICD) as modulator of gene expression, apoptosis, and cytoskeletal dynamics-relevance for Alzheimer's disease

Since the discovery of the amyloid precursor protein (APP) in 1987, extensive research has been conducted analyzing the APP-derived beta-amyloid (Abeta) which is found in massive quantities in senile plaques of Alzheimer disease (AD) patients. Numerous studies over the last two decades have demonstrated the neurotoxic properties of Abeta. However, it is still unclear whether Abeta neurotoxicity is an initial cause or rather a late event in the pathophysiology of AD. The understanding of preclinical AD-related pathophysiological mechanisms is of significant interest in the identification of potential pharmacological targets. In this context another APP-derived cleavage product, the amyloid precursor protein intracellular domain (AICD), has sparked considerable research interest over the last 7 years. Different AICD levels as a result of gamma-secretase activity may contribute to early pathophysiological mechanisms in AD. However, the relevance of AICD is being discussed highly controversially amongst AD researchers. This review summarizes recent findings in terms of the origin of AICD by regulated intramembrane proteolysis; its structure, binding factors, and post-translational modifications; and its putative role in gene transcription, apoptosis, and cytoskeletal dynamics.