Nephrocystin-1 interacts directly with Ack1 and is expressed in human collecting duct

Scalp Tumor and Hydroureteronephrosis in Patients with Nephronophthisis and Homozygous NPHP1 Deletion

Homozygous deletion of NPHP1 can lead to isolated nephronophthisis (NPHP) and syndromic disorders. However, the phenotype of scalp tumor and hydroureteronephrosis in NPHP patients with homozygous deletion of NPHP1 has not been reported. Clinical data, laboratory results, and genetic testing of 4 NPHP patients were collected. Examination of their eyes, heart, and urinary tract and of their hepatobiliary, skeletal, and central nervous systems was evaluated. Isolated NPHP was observed in 1 case, and syndromic disorders were observed in the other 3 patients. Their syndromic disorders showed NPHP combined with central nervous system defects, eye involvement, scalp tumor, arachnoid cyst, or hydroureteronephrosis. Large homozygous deletions covering the whole NPHP1 gene locus were identified in all 4 patients. We report a novel phenotype of scalp tumor and hydroureteronephrosis in NPHP patients with homozygous deletion of NPHP1, paving an avenue for further research on NPHP1-associated deformity in the skin and the urinary system.

Fluid shear stress triggers cholesterol biosynthesis and uptake in inner medullary collecting duct cells, independently of nephrocystin-1 and nephrocystin-4

Renal epithelial cells are subjected to fluid shear stress of urine flow. Several cellular structures act as mechanosensors-the primary cilium, microvilli and cell adhesion complexes-that directly relay signals to the cytoskeleton to regulate various processes including cell differentiation and renal cell functions. Nephronophthisis (NPH) is an autosomal recessive tubulointerstitial nephropathy leading to end-stage kidney failure before adulthood. NPHP1 and NPHP4 are the major genes which code for proteins that form a complex at the transition zone of the primary cilium, a crucial region required for the maintenance of the ciliary composition integrity. These two proteins also interact with signaling components and proteins associated with the actin cytoskeleton at cell junctions. Due to their specific subcellular localization, we wondered whether NPHP1 and NPHP4 could ensure mechanosensory functions. Using a microfluidic set up, we showed that murine inner medullary collecting ductal cells invalidated for Nphp1 or Nphp4 are more responsive to immediate shear exposure with a fast calcium influx, and upon a prolonged shear condition, an inability to properly regulate cilium length and actin cytoskeleton remodeling. Following a transcriptomic study highlighting shear stress-induced gene expression changes, we showed that prolonged shear triggers both cholesterol biosynthesis pathway and uptake, processes that do not seem to involve neither NPHP1 nor NPHP4. To conclude, our study allowed us to determine a moderate role of NPHP1 and NPHP4 in flow sensation, and to highlight a new signaling pathway induced by shear stress, the cholesterol biosynthesis and uptake pathways, which would allow cells to cope with mechanical stress by strengthening their plasma membrane through the supply of cholesterol.

A genotype-to-phenotype approach suggests under-reporting of single nucleotide variants in nephrocystin-1 (NPHP1) related disease (UK 100,000 Genomes Project)

Autosomal recessive whole gene deletions of nephrocystin-1 (NPHP1) result in abnormal structure and function of the primary cilia. These deletions can result in a tubulointerstitial kidney disease known as nephronophthisis and retinal (Senior-Løken syndrome) and neurological (Joubert syndrome) diseases. Nephronophthisis is a common cause of end-stage kidney disease (ESKD) in children and up to 1% of adult onset ESKD. Single nucleotide variants (SNVs) and small insertions and deletions (Indels) have been less well characterised. We used a gene pathogenicity scoring system (GenePy) and a genotype-to-phenotype approach on individuals recruited to the UK Genomics England (GEL) 100,000 Genomes Project (100kGP) (n = 78,050). This approach identified all participants with NPHP1-related diseases reported by NHS Genomics Medical Centres and an additional eight participants. Extreme NPHP1 gene scores, often underpinned by clear recessive inheritance, were observed in patients from diverse recruitment categories, including cancer, suggesting the possibility of a more widespread disease than previously appreciated. In total, ten participants had homozygous CNV deletions with eight homozygous or compound heterozygous with SNVs. Our data also reveals strong in-silico evidence that approximately 44% of NPHP1 related disease may be due to SNVs with AlphaFold structural modelling evidence for a significant impact on protein structure. This study suggests historical under-reporting of SNVS in NPHP1 related diseases compared with CNVs.

Many Genes-One Disease? Genetics of Nephronophthisis (NPHP) and NPHP-Associated Disorders

Nephronophthisis (NPHP) is a renal ciliopathy and an autosomal recessive cause of cystic kidney disease, renal fibrosis, and end-stage renal failure, affecting children and young adults. Molecular genetic studies have identified more than 20 genes underlying this disorder, whose protein products are all related to cilia, centrosome, or mitotic spindle function. In around 15% of cases, there are additional features of a ciliopathy syndrome, including retinal defects, liver fibrosis, skeletal abnormalities, and brain developmental disorders. Alongside, gene identification has arisen molecular mechanistic insights into the disease pathogenesis. The genetic causes of NPHP are discussed in terms of how they help us to define treatable disease pathways including the cyclic adenosine monophosphate pathway, the mTOR pathway, Hedgehog signaling pathways, and DNA damage response pathways. While the underlying pathology of the many types of NPHP remains similar, the defined disease mechanisms are diverse, and a personalized medicine approach for therapy in NPHP patients is likely to be required.

The Cdc42-associated kinase ACK1 is not autoinhibited but requires Src for activation

The non-RTK (receptor tyrosine kinase) ACK1 [activated Cdc42 (cell division cycle 42)-associated kinase 1] binds a number of RTKs and is associated with their endocytosis and turnover. Its mode of activation is not well established, but models have suggested that this is an autoinhibited kinase. Point mutations in its SH3 (Src homology 3)- or EGF (epidermal growth factor)-binding domains have been reported to activate ACK1, but we find neither of the corresponding W424K or F820A mutations do so. Indeed, deletion of the various ACK1 domains C-terminal to the catalytic domain are not associated with increased activity. A previous report identified only one major tyrosine phosphorylated protein of 60 kDa co-purified with ACK1. In a screen for new SH3 partners for ACK1 we found multiple Src family kinases; of these c-Src itself binds best. The SH2 and SH3 domains of Src interact with ACK1 Tyr518 and residues 623-652 respectively. Src targets the ACK1 activation loop Tyr284, a poor autophosphorylation site. We propose that ACK1 fails to undergo significant autophosphorylation on Tyr284 in vivo because it is basophilic (whereas Src is acidophilic). Subsequent ACK1 activation downstream of receptors such as EGFR (EGF receptor) (and Src) promotes turnover of ACK1 in vivo, which is blocked by Src inhibitors, and is compromised in the Src-deficient SYF cell line. The results of the present study can explain why ACK1 is responsive to so many external stimuli including RTKs and integrin ligation, since Src kinases are commonly recruited by multiple receptor systems.

Nephronophthisis: a genetically diverse ciliopathy

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease and a leading genetic cause of established renal failure (ERF) in children and young adults. Early presenting symptoms in children with NPHP include polyuria, nocturia, or secondary enuresis, pointing to a urinary concentrating defect. Renal ultrasound typically shows normal kidney size with increased echogenicity and corticomedullary cysts. Importantly, NPHP is associated with extra renal manifestations in 10-15% of patients. The most frequent extrarenal association is retinal degeneration, leading to blindness. Increasingly, molecular genetic testing is being utilised to diagnose NPHP and avoid the need for a renal biopsy. In this paper, we discuss the latest understanding in the molecular and cellular pathogenesis of NPHP. We suggest an appropriate clinical management plan and screening programme for individuals with NPHP and their families.

Nephronophthisis

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease and the most frequent genetic cause of end-stage renal disease up to the third decade of life. It is caused by mutations in 11 different genes, denoted nephrocystins (NPHP1-11, NPHP1L). As an increasing number of these genes are identified, our knowledge of nephronophthisis is changing, thereby improving our understanding of the pathomechanisms in NPHP. Recent publications have described ciliary expression of nephrocystins together with other cystoproteins, such as polycystins 1 and 2 and fibrocystin. These findings have shifted our focus to a pathomechanism involving defects in ciliary function (ciliopathy) and planar cell polarity (PCP). In addition, discoveries of new nephrocystin genes have shown that the disease spectrum of NPHP is much broader than previously anticipated. Different forms of mutations within the same NPHP gene can cause different disease severity. In this review, we highlight the different hypotheses on the pathomechanisms for NPHP and underline the clinical variability of this disease. The clinical spectrum has become even more complex with the possibility of oligogenicity in NPHP.

Shepherding AKT and androgen receptor by Ack1 tyrosine kinase

Ack1 (also known as ACK, TNK2, or activated Cdc42 kinase) is a structurally unique non-receptor tyrosine kinase that is expressed in diverse cell types. It integrates signals from plethora of ligand-activated receptor tyrosine kinases (RTKs), for example, MERTK, EGFR, HER2, PDGFR and insulin receptor to initiate intracellular signaling cascades. Ack1 transduces extracellular signals to cytosolic and nuclear effectors such as the protein kinase AKT/PKB and androgen receptor (AR), to promote cell survival and growth. While tyrosine phosphorylation of AR at Tyr267 regulates androgen-independent recruitment of AR to the androgen-responsive enhancers and transcription of AR target genes to drive prostate cancer progression, phosphorylation of an evolutionarily conserved Tyrosine 176 in the kinase domain of AKT is essential for mitotic progression and positively correlates with breast cancer progression. In contrast to AR and AKT, Ack1-mediated phosphorylation of the tumor suppressor Wwox at Tyr287 lead to rapid Wwox polyubiquitination followed by degradation. Thus, by its ability to promote tumor growth by negatively regulating tumor suppressor such as Wwox and positively regulating pro-survival factors such as AKT and AR, Ack1 is emerging as a critical player in cancer biology. In this review, we discuss recent advances in understanding the physiological functions of Ack1 signaling in normal cells and the consequences of its hyperactivation in various cancers.

Nephronophthisis

Nephronophthisis (NPHP) is an autosomal recessive kidney disorder characterized by chronic tubulointerstitial nephritis and leading to end-stage renal failure. NPHP as a renal entity is often part of a multisystem disorder and has been associated with many syndromes including Joubert syndrome (and related disorders) and Senior-Loken syndrome. Recent molecular genetic advances have allowed identification of several genes underlying NPHP. Most of these genes express their protein products, named nephrocystins, in primary cilial/basal body structures. Some nephrocystins are part of adherens junction and focal adhesion kinase protein complexes. This shared localization suggests that common pathogenic mechanisms within the kidney underlie this disease. Functional studies implicate nephrocystins in planar cell polarity pathways, which may be crucial for renal development and maintenance of tubular architecture.