TBC1 Domain Containing Kinase Research Articles

Suppression of TBCK enhances TRAIL-mediated apoptosis by causing the inactivation of the akt signaling pathway in human renal carcinoma Caki-1 cells.

TBC1 domain-containing kinase (TBCK) protein functions as a growth suppressor in certain cell types and as a tumor promoter in others. Although TBCK knockdown increases the responsiveness of cancer cells to anticancer drugs, the detailed mechanisms by which TBCK knockdown increases susceptibility to anticancer drugs remain unknown. This study analyzed the role of TBCK in sensitivities to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and doxorubicin in human renal cancer cells. Flow cytometry was employed to evaluate the extent of apoptosis. Western blotting, transient transfection, and lentiviral infection techniques were conducted to investigate the impact of TBCK on apoptosis-related protein expression and mitogen-activated protein kinase (MAPK). TBCK knockdown in renal cancer cells inhibits ERK and Akt signaling pathways and increases TRAIL and doxorubicin sensitivity. In TBCK-knockdown Caki-1 cells, ERK and Akt phosphorylation was suppressed compared to control cell lines, and TRAIL and doxorubicin sensitivities were increased in these cells. In addition, the phosphorylation of PDK1 was suppressed in TBCK-suppressed cells, indicating that TBCK may be involved in the PDK1 and Akt signaling pathways. The introduction of dominantly active Akt into TBCK-suppressed cells restored their sensitivity to TRAIL. In addition, TBCK downregulation enhanced TRAIL sensitivity in different renal cancer cell lines. These data suggest that TBCK could potentially have a crucial function in influencing the effects of anti-cancer drugs including TRAIL by modulating the signaling pathway involving Akt and PDK1 in human renal cancer cells.

Raising awareness of TBC1 domain‐containing kinase (TBCK) epileptic encephalopathy among Puerto Rican children

AbstractBackgroundTBC1 domain‐containing kinase (TBCK) syndrome is a rare autosomal recessive genetic disorder that presents with infantile hypotonia, intellectual disability, motor impairment, and drug‐resistant epilepsy. The abnormal TBCK protein alters the mammalian target of rapamycin complex 1 (mTORC1), leading to accumulation of autophagic vesicles within fibroblasts. Thirty‐five previously reported individuals with TBCK were identified.MethodsWe present four children with TBCK due to the p.R126X (p.ARG126*) mutation, a variant predominating among children of Puerto Rican descent. This mutation has been associated with TBCK‐encephaloneuropathy or Boricua syndrome.DiscussionThese four of our patients were diagnosed within a span of 6 months, suggesting that the prevalence of the syndrome could be higher than expected among individuals from Puerto Rico. We believe this finding was largely due to the increasing availability and affordability of modern genetic testing in Puerto Rico, illustrating the importance of equitable access to genetic testing to all pediatric patients with similar symptomatology. Prompt diagnosis facilitates appropriate medical management and prognosis counseling.

Multiple functions of TBCK protein in neurodevelopment disorders and tumors.

TBC1 domain containing kinase (TBCK) protein is composed of three conserved domains, including N-terminal Serine/Threonine kinase domain, central TBC domain and C-terminal rhodanese homology domain (RHOD). A total of 9 different transcripts (classified as long and short TBCK) generated by alternative splicing have been reported in different cell lines. Exogenous expression of long TBCK has been identified to function as a suppressor of cell growth in certain cell types. On the contrary, TBCK has also been reported to serve a tumor-promoting role in other cell lines, indicating that TBCK might function differentially, depending on the context in different cellular environments. Furthermore, deleterious homozygous or compound heterozygous mutations identified by whole-exome sequencing in the TBCK gene could ablate the function of TBCK, further impacting the mTOR signaling pathway and leading to neurogenetic disorders, such as hypotonia, global developmental delay, facial dysmorphic features and brain abnormalities. However, as a poorly explored protein, there are a lot of studies associated with the functions of TBCK that need to be performed in the future. The present review summarizes data regarding the structural features and potential roles of TBCK in developmental and neurological diseases and tumorigenesis. Future prospects of TBCK research lie in revealing numerous biological functions of TBCK.

Myopathic changes associated with psychomotor delay and seizures caused by a novel homozygous mutation in TBCK

Biallelic mutations in TBC1-domain containing kinase (TBCK) lead to hypotonia, global developmental delay with severe cognitive and motor deficits, and variable presentation of dysmorphic facial features and brain malformations. It remains unclear whether hypotonia in these individuals is purely neurogenic, or also caused by progressive muscle disease. Whole exome sequencing was performed on a family diagnosed with nonspecific myopathic changes by means of histological analysis and immunohistochemistry of muscle biopsy samples. A novel homozygous truncation in TBCK was found in two sisters diagnosed with muscle disease and severe psychomotor delay. TBCK was completely absent in these patients. Our findings identify a novel early truncating variant in TBCK associated with a severe presentation and add muscle disease to the variability of phenotypes associated with TBCK mutations. Inconsistent genotype/phenotype correlation could be ascribed to the multiple roles of TBCK in intracellular signaling and endolysosomal function in different tissues.

MiR-1208 Increases the Sensitivity to Cisplatin by Targeting TBCK in Renal Cancer Cells.

MicroRNAs (miRNAs) can be used to target a variety of human malignancies by targeting their oncogenes or tumor suppressor genes. Recent evidence has shown that miRNA-1208 (miR-1208) was rarely expressed in a variety of cancer cells, suggesting the possibility that miR-1208 functions as a tumor suppressor gene. Herein, ectopic expression of miR-1208 induced the accumulation of sub-G1 populations and the cleavage of procaspase-3 and PARP, which could be prevented by pre-treatment with the pan-caspase inhibitor, Z-VAD. In addition, miR-1208 increased the susceptibility to cisplatin and TRAIL in Caki-1 cells. Luciferase reporter assay results showed that miR-1208 negatively regulates TBC1 domain containing kinase (TBCK) expression by binding to the miR-1208 binding sites in the 3′-untranslated region of TBCK. In addition, miR-1208 specifically repressed TBCK expression at the transcriptional level. In contrast, inhibition of endogenous miR-1208 by anti-miRs resulted in an increase in TBCK expression. Downregulation of TBCK induced by TBCK-specific siRNAs increased susceptibility to cisplatin and TRAIL. These findings suggest that miR-1208 acts as a tumor suppressor and targets TBCK directly, thus possessing great potential for use in renal cancer therapy.

Neuropathologic Findings in a Child with a Novel Variant of TBCK-Related Encephaloneuronopathy

AbstractA 3-year-old girl with developmental delays, hypotonia, and generalized seizures was diagnosed with a novel variant of a heterozygous mutation in the TBC1 domain containing kinase (TBCK) gene. Postmortem findings revealed severe hypotrophy of cerebral white matter, hypogenesis of the corpus callosum with reduced myelination and oligodendrocyte populations, and reactive gliosis, and venous angiomas of the cerebrum, brainstem, and cerebellum white matter. This report is the first to link a TBCK gene mutation to impaired white matter development with the targeting of central nervous system myelin and oligodendrocytes. The mechanism may involve inhibition of signaling through (mTORC1).

Homozygous TBC1 domain-containing kinase (TBCK) mutation causes a novel lysosomal storage disease \u2013 a new type of neuronal ceroid lipofuscinosis (CLN15)?

Homozygous mutation of TBC1 domain-containing kinase (TBCK) is the cause of a very recently defined severe childhood disorder, which is characterized by severe hypotonia, global developmental delay, intellectual disability, epilepsy, characteristic facies and premature death. The link between TBCK loss of function and symptoms in patients with TBCK deficiency disorder (TBCK-DD) remains elusive. Here we demonstrate for the first time the histopathological characteristics of TBCK deficiency consisting of 1) a widespread and massive accumulation of lipofuscin storage material in neurons of the central nervous system without notable neuronal degeneration, 2) storage deposits in few astrocytes, 3) carbohydrate-rich deposits in brain, spleen and liver and 4) vacuolated lymphocytes. Biochemical examinations ruled out more than 20 known lysosomal storage diseases. These investigations strikingly uncover TBCK-DD as a novel type of lysosomal storage disease which is characterized by different storage products rather than one specific type of accumulated material. Due to the clear predominance of intraneuronal lipofuscin storage material and the characteristic clinical presentation we propose to classify this disease as a new subtype of neuronal ceroid lipofuscinosis (CLN15). Our results and previous reports suggest an autophagosomal-lysosomal dysfunction caused by enhanced mTORC1-mediated autophagosome formation and reduced Rab-mediated autophagosome-lysosome fusion, thus disclosing potential novel targets for therapeutic approaches in TBCK-DD.

Further delineation of TBCK - Infantile hypotonia with psychomotor retardation and characteristic facies type 3

Deleterious homozygous or compound heterozygous mutations in the TBCK (TBC1-domain-containing kinase) gene (implicated in the MTOR pathway) produce profound hypotonia, global developmental delay, facial dysmorphic features, and brain abnormalities. The disorder has been named “infantile hypotonia with psychomotor retardation and characteristic facies-3” (IHPRF3). Here we present two sisters with a novel mutation in TBCK (NM_001163435.2: c.753dup; p.(Lys252*)) who have this ultrarare disorder. We have reviewed the literature on the 33 previously reported cases to provide a characterization of this emerging phenotype. Pathogenic mutations in TBCK have a predominant involvement of the Central Nervous System with a progressive pattern, leading to the conclusion where pathogenic mutations of the said gene lead to a progressive neurodegenerative disease. This report adds novel mutation and features to this complex phenotype. Further investigation is required to understand the pathogenesis of TBCK.

Mutations in TBCK, Encoding TBC1-Domain-Containing Kinase, Lead to a Recognizable Syndrome of Intellectual Disability and Hypotonia

Through an international multi-center collaboration, 13 individuals from nine unrelated families and affected by likely pathogenic biallelic variants in TBC1-domain-containing kinase (TBCK) were identified through whole-exome sequencing. All affected individuals were found to share a core phenotype of intellectual disability and hypotonia, and many had seizures and showed brain atrophy and white-matter changes on neuroimaging. Minor non-specific facial dysmorphism was also noted in some individuals, including multiple older children who developed coarse features similar to those of storage disorders. TBCK has been shown to regulate the mammalian target of rapamycin (mTOR) signaling pathway, which is also stimulated by exogenous leucine supplementation. TBCK was absent in cells from affected individuals, and decreased phosphorylation of phospho-ribosomal protein S6 was also observed, a finding suggestive of downregulation of mTOR signaling. Lastly, we demonstrated that activation of the mTOR pathway in response to L-leucine supplementation was retained, suggesting a possible avenue for directed therapies for this condition.

Recessive Inactivating Mutations in TBCK, Encoding a Rab GTPase-Activating Protein, Cause Severe Infantile Syndromic Encephalopathy

Infantile encephalopathies are a group of clinically and biologically heterogeneous disorders for which the genetic basis remains largely unknown. Here, we report a syndromic neonatal encephalopathy characterized by profound developmental disability, severe hypotonia, seizures, diminished respiratory drive requiring mechanical ventilation, brain atrophy, dysgenesis of the corpus callosum, cerebellar vermis hypoplasia, and facial dysmorphism. Biallelic inactivating mutations in TBCK (TBC1-domain-containing kinase) were independently identified by whole-exome sequencing as the cause of this condition in four unrelated families. Matching these families was facilitated by the sharing of phenotypic profiles and WES data in a recently released web-based tool (Geno2MP) that links phenotypic information to rare variants in families with Mendelian traits. TBCK is a putative GTPase-activating protein (GAP) for small GTPases of the Rab family and has been shown to control cell growth and proliferation, actin-cytoskeleton dynamics, and mTOR signaling. Two of the three mutations (c.376C>T [p.Arg126(∗)] and c.1363A>T [p.Lys455(∗)]) are predicted to truncate the protein, and loss of the major TBCK isoform was confirmed in primary fibroblasts from one affected individual. The third mutation, c.1532G>A (p.Arg511His), alters a conserved residue within the TBC1 domain. Structural analysis implicated Arg511 as a required residue for Rab-GAP function, and insilico homology modeling predicted impaired GAP function in the corresponding mutant. These results suggest that loss of Rab-GAP activity is the underlying mechanism of disease. In contrast to other disorders caused by dysregulated mTOR signaling associated with focal or global brain overgrowth, impaired TBCK function results in progressive loss of brain volume.

TBCK Influences Cell Proliferation, Cell Size and mTOR Signaling Pathway

Mammalian target of rapamycin (mTOR) is a central regulator for both cell proliferation and cell growth; however, little is known about the regulation of mTOR expression at the transcriptional level. Here, we provide evidences that a conserved human protein TBCK (TBC1 domain containing kinase) is involved in the regulation of mTOR signaling pathway. Depletion of TBCK significantly inhibits cell proliferation, reduces cell size, and disrupts the organization of actin, but not microtubule. Knockdown of TBCK induces a significant decrease in the protein levels of components of mTOR complex (mTORC), and suppresses the activity of mTOR signaling, but not MAPK or PDK1/Akt pathway. Further results show that TBCK influences the expression of mTORC components at the transcriptional level. Thus, these data suggest that TBCK may play an important role in cell proliferation, cell growth and actin organization possibly by modulating mTOR pathway.