KCTD1 is a new modulator of the KCASH family of Hedgehog suppressors.

The Sonic Hedgehog (Hh) signal transduction pathway plays a critical role in many developmental processes and, when deregulated, may contribute to several cancers, including basal cell carcinoma, medulloblastoma, colorectal, prostate, and pancreatic cancer. In recent years, several Hh inhibitors have been developed, mainly acting on the Smo receptor. However, drug resistance due to Smo mutations or non-canonical Hh pathway activation highlights the need to identify further mechanisms of Hh pathway modulation. Among these, deacetylation of the Hh transcription factor Gli1 by the histone deacetylase HDAC1 increases Hh activity. On the other end, the KCASH family of oncosuppressors binds HDAC1, leading to its ubiquitination and subsequent proteasomal degradation, leaving Gli1 acetylated and not active. It was recently demonstrated that the potassium channel containing protein KCTD15 is able to interact with KCASH2 protein and stabilize it, enhancing its effect on HDAC1 and Hh pathway. KCTD15 and KCTD1 proteins share a high homology and are clustered in a specific KCTD subfamily. We characterize here KCTD1 role on the Hh pathway. Therefore, we demonstrated KCTD1 interaction with KCASH1 and KCASH2 proteins, and its role in their stabilization by reducing their ubiquitination and proteasome-mediated degradation. Consequently, KCTD1 expression reduces HDAC1 protein levels and Hh/Gli1 activity, inhibiting Hh dependent cell proliferation in Hh tumour cells. Furthermore, analysis of expression data on publicly available databases indicates that KCTD1 expression is reduced in Hh dependent MB samples, compared to normal cerebella, suggesting that KCTD1 may represent a new putative target for therapeutic approaches against Hh-dependent tumour.

The Oncosuppressive Properties of KCTD1: Its Role in Cell Growth and Mobility.

The KCTD protein family is traditionally regarded as proteins that play key roles in neurological physiopathology. However, new studies are increasingly demonstrating their involvement in many other biological processes, including cancers. This is particularly evident for KCTD proteins not involved in protein ubiquitination and degradation, such as KCTD1. We explored the role of KCTD1 in colorectal cancer by knocking down this protein in the human colon adenocarcinoma cell line, SW480. We re-assessed its ability to downregulate ß-catenin, a central actor in the WNT/ß-catenin signalling pathway. Interestingly, opposite effects are observed when the protein is upregulated in CACO2 colorectal cancer cells. Moreover, interrogation of the TCGA database indicates that KCTD1 downregulation is associated with ß-catenin overexpression in colorectal cancer patients. Indeed, knocking down KCTD1 in SW480 cells led to a significant increase in their motility and stemness, two important tumorigenesis traits, suggesting an oncosuppressor role for KCTD1. It is worth noting that similar effects are induced on colorectal cancer cells by the misregulation of KCTD12, a protein that is distantly related to KCTD1. The presented results further expand the spectrum of KCTD1 involvement in apparently unrelated physiopathological processes. The similar effects produced on colorectal cancer cell lines by KCTD1 and KCTD12 suggest novel, previously unreported analogous activities among members of the KCTD protein family.

KCTD1 and Scalp-Ear-Nipple ('Finlay-Marks') syndrome may be associated with myopia and Thin basement membrane nephropathy through an effect on the collagen IV α3 and α4 chains.

INTRODUCTION: Scalp-Ear-Nipple syndrome is caused by pathogenic KCTD1 variants and characterised by a scalp defect, prominent ears, and rudimentary breasts. We describe here further clinical associations in the eye and kidney. METHODS: Fifteen affected members from two unrelated families with p.(Ala30Glu) or p.(Pro31Leu) in KCTD1 were examined for ocular and renal abnormalities. The relevant proteins were studied in the eye and kidney, and the mutation consequences determined from mouse knockout models. RESULTS: Five males and 10 females with a median age of 40 years (range 1-70) with pathogenic variants p.(Ala30Glu) (n = 12) or p.(Pro31Leu) (n = 3) in KCTD1 were studied. Of the 6 who underwent detailed ophthalmic examination, 5 (83%) had low myopic astigmatism, the mean spherical equivalent of 10 eyes was 2.38D, and one (17%) had hypermetropic astigmatism. One female had a divergent strabismus.Five individuals had renal cysts (5/15, 33%), with renal biopsy in one demonstrating a thinned glomerular basement membrane identical to that seen in Thin basement membrane nephropathy (AD Alport syndrome).In the eye, KCTD1 and its downstream targets, TFAP2, and the collagen IV α3 and α4 chains localised to the cornea and near the retinal amacrine cells. In the kidney, all these proteins except TFAP2 were expressed in the podocytes and distal tubules. TFAP2B and COL4A4 knockout mice also had kidney cysts, and COL4A3 and COL4A4 knockout mice had myopia. CONCLUSION: Individuals with a pathogenic KCTD1 variant may have low myopic astigmatism and represent a further rare genetic cause for a thinned glomerular basement membrane.

Magnesium and Calcium Homeostasis Depend on KCTD1 Function in the Distal Nephron.

Magnesium (Mg2+) homeostasis depends on active transcellular Mg2+ reuptake from urine in distal convoluted tubules (DCTs) via the Mg2+ channel TRPM6, whose activity has been proposed to be regulated by EGF. Calcium (Ca2+) homeostasis depends on paracellular reabsorption in the thick ascending limbs of Henle (TALs). KCTD1 promotes terminal differentiation of TALs/DCTs, but how its deficiency affects urinary Mg2+ and Ca2+ reabsorption is unknown. Here, this study shows that DCT1-specific KCTD1 inactivation leads to hypomagnesemia despite normal TRPM6 levels because of reduced levels of the sodium chloride co-transporter NCC, whereas Mg2+ homeostasis does not depend on EGF. Moreover, KCTD1 deficiency impairs paracellular urinary Ca2+ and Mg2+ reabsorption in TALs because of reduced NKCC2/claudin-16/-19 and increased claudin-14 expression, leading to hypocalcemia and consequently to secondary hyperparathyroidism and progressive metabolic bone disease. Thus, KCTD1 regulates urinary reabsorption of Mg2+ and Ca2+ by inducing expression of NCC in DCTs and NKCC2/claudin-16/-19 in TALs.

AP-2ß/KCTD1 Control Distal Nephron Differentiation and Protect against Renal Fibrosis.

The developmental mechanisms that orchestrate differentiation of specific nephron segments are incompletely understood, and the factors that maintain their terminal differentiation after nephrogenesis remain largely unknown. Here, the transcription factor AP-2ß is shown to be required for the differentiation of distal tubule precursors into early stage distal convoluted tubules (DCTs) during nephrogenesis. In contrast, its downstream target KCTD1 is essential for terminal differentiation of early stage DCTs into mature DCTs, and impairment of their terminal differentiation owing to lack of KCTD1 leads to a severe salt-losing tubulopathy. Moreover, sustained KCTD1 activity in the adult maintains mature DCTs in this terminally differentiated state and prevents renal fibrosis by repressing ß-catenin activity, whereas KCTD1 deficiency leads to severe renal fibrosis. Thus, the AP-2ß/KCTD1 axis links a developmental pathway in the nephron to the induction and maintenance of terminal differentiation of DCTs that actively prevents their de-differentiation in the adult and protects against renal fibrosis.

KCTD1: A novel modulator of adipogenesis through the interaction with the transcription factor AP2α.

Adipogenesis has an important role in regulating energy balance, tissue homeostasis and disease pathogenesis. 3T3-L1 preadipocytes have been widely used as an in vitro model for studying adipocyte differentiation. We here show that KCTD1, a member of the potassium channel containing tetramerization domain proteins, plays an active role in adipogenesis. In particular, we show KCTD1 expression 3T3-L1 cells increases upon adipogenesis induction. Treatment of 3T3-L1 preadipocytes with Kctd1-specific siRNA inhibited the differentiation, as indicated by reduction of expression of the specific adipogenic markers C/ebpα, Pparγ2, Glut4, and Adiponectin. Moreover, we also show that the protein physically interacts with the transcription factor AP2α, a known inhibitor of adipogenesis, both in vitro and in cells. Interestingly, our data indicate that KCTD1 promotes adipogenesis through the interaction with AP2α and by removing it from the nucleus. Collectively, these findings disclose a novel role for KCTD1 and pave the way for novel strategies aimed at modulating adipogenesis.

No clinical utility of common polymorphisms in IGF1, IRS1, GCKR, PPARG, GCK1 and KCTD1 genes previously associated with insulin resistance in overweight children from Romania and Moldova.

Background Previous genome-wide association studies (GWAS) identified IGF1, IRS1, GCKR, PPARG, GCK1 and KCTD1 as candidate genes for insulin resistance and type 2 diabetes (T2D). We investigated the associations of these previously reported common variants in these genes with insulin resistance in overweight children from Romania and Moldova. Methods Six single nucleotide polymorphisms (SNPs), IGF1 (rs35767), IRS1 (rs2943634), GCKR (rs780094), PPARG (rs1801282), GCK1 (rs1799884) and KCTD15 (rs29941), were genotyped in 100 overweight children along with clinical and metabolic parameters. Homeostatic model assessment of insulin resistance (HOMA-IR) above 3.4 (defining insulin resistance) was used as the outcome. Results Children differed in insulin resistance status despite having similar body mass index (BMI) standard deviation scores (SDS) (World Health Organization, [WHO] reference). The identified predictors for altered insulin metabolism were higher cholesterol levels, higher diastolic blood pressure and higher waist-to-hip-ratio (as a marker for increased abdominal fat). None of the SNPs showed significant association with increase in the risk for insulin resistance in children (p range=0.478-0.724; odds ratio [OR] range=1.924-4.842); however, the risk allele in GCKR (rs780094, p=0.06, OR=6.871) demonstrated near statistical significance. Conclusions The interrogated risk alleles did not show any significant association with insulin resistance in children in our cohort; however, the GCKR (rs780094) might be a viable candidate in larger cohorts. The lack of replication of the proposed association may point to differences in linkage disequilibrium or effect modifiers across studies.

Standardized, systemic phenotypic analysis reveals kidney dysfunction as main alteration of Kctd1 I27N mutant mice.

BACKGROUND: Increased levels of blood plasma urea were used as phenotypic parameter for establishing novel mouse models for kidney diseases on the genetic background of C3H inbred mice in the phenotype-driven Munich ENU mouse mutagenesis project. The phenotypically dominant mutant line HST014 was established and further analyzed. METHODS: Analysis of the causative mutation as well as the standardized, systemic phenotypic analysis of the mutant line was carried out. RESULTS: The causative mutation was detected in the potassium channel tetramerization domain containing 1 (Kctd1) gene which leads to the amino acid exchange Kctd1 I27N thereby affecting the functional BTB domain of the protein. This line is the first mouse model harboring a Kctd1 mutation. Kctd1 I27N homozygous mutant mice die perinatally. Standardized, systemic phenotypic analysis of Kctd1 I27N heterozygous mutants was carried out in the German Mouse Clinic (GMC). Systematic morphological investigation of the external physical appearance did not detect the specific alterations that are described in KCTD1 mutant human patients affected by the scalp-ear-nipple (SEN) syndrome. The main pathological phenotype of the Kctd1 I27N heterozygous mutant mice consists of kidney dysfunction and secondary effects thereof, without gross additional primary alterations in the other phenotypic parameters analyzed. Genome-wide transcriptome profiling analysis at the age of 4 months revealed about 100 differentially expressed genes (DEGs) in kidneys of Kctd1 I27N heterozygous mutants as compared to wild-type controls. CONCLUSIONS: In summary, the main alteration of the Kctd1 I27N heterozygous mutants consists in kidney dysfunction. Additional analyses in 9-21 week-old heterozygous mutants revealed only few minor effects.