Experience alters hippocampal and cortical network communication via a KIBRA-dependent mechanism

Synaptic plasticity is hypothesized to underlie "replay" of salient experience during hippocampal sharp-wave/ripple (SWR)-based ensemble activity and to facilitate systems-level memory consolidation coordinated by SWRs and cortical sleep spindles. It remains unclear how molecular changes at synapses contribute to experience-induced modification of network function. The synaptic protein KIBRA regulates plasticity and memory. To determine the impact of KIBRA-regulated plasticity on circuit dynamics, we recorded in vivo neural activity from wild-type (WT) mice and littermates lacking KIBRA and examined circuit function before, during, and after novel experience. In WT mice, experience altered population activity and oscillatory dynamics in a manner consistent with incorporation of new information content in replay and enhanced hippocampal-cortical communication. While baseline SWR features were normal in KIBRA conditional knockout (cKO) mice, experience-dependent alterations in SWRs were absent. Furthermore, intra-hippocampal and hippocampal-cortical communication during SWRs was disrupted following KIBRA deletion. These results indicate molecular mechanisms that underlie network-level adaptations to experience.

Pathological Significance of Kidney and Brain Expressed Protein (KIBRA) in Clear Cell Renal Cell Carcinoma

BACKGROUND/AIM

Kidney and brain expressed protein (KIBRA), a member of the WW domain-containing protein family, has an important role in tumour growth and progression in various cancers. However, the pathological significance of KIBRA expression in clear cell renal cell carcinoma (ccRCC) tissues is not fully understood. The aim of this study was to clarify the pathological significance and prognostic roles of KIBRA expression in patients with ccRCC.

MATERIALS AND METHODS

KIBRA immunoreactivity, proliferation index (PI; with anti-Ki-67 antibody), apoptotic index (AI; using anti-cleaved caspase-3), and large tumour suppressor kinases (LATS-2) were evaluated in 157 ccRCC specimens by immunohistochemistry. Fifty normal kidney tissues were also evaluated as controls. The relationships between KIBRA expression and these cancer-related variables as well as clinicopathological features and survival were analysed.

RESULTS

Moderate to strong immunoreactivity of KIBRA was identified in all normal kidney tissues; however, ccRCC cells with strong KIBRA expression was rare. The immunoreactivity score (IRS) of KIBRA was negatively associated with grade, T stage, tumour diameter, and metastasis. Kaplan-Meier survival curves showed that high KIBRA expression was a favourite predictor for overall survival. KIBRA IRS was negatively associated with PI and positively associated with the IRS of LATS-2 by univariate analysis. In addition, multivariate analysis showed that KIBRA was significantly associated with PI.

CONCLUSION

KIBRA demonstrated important roles as a tumour suppressor in ccRCC. In addition, its expression was significantly associated with survival in these patients. Several such KIBRA-related functions were speculated to be modulated by cancer cell proliferation and LATS-2.

Hippo-released WWC1 facilitates AMPA receptor regulatory complexes for hippocampal learning

Learning and memory rely on changes in postsynaptic glutamergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type receptor (AMPAR) number, spatial organization, and function. The Hippo pathway component WW and C2 domain-containing protein 1 (WWC1) regulates AMPAR surface expression and impacts on memory performance. However, synaptic binding partners of WWC1 and its hierarchical position in AMPAR complexes are largely unclear. Using cell-surface proteomics in hippocampal tissue of Wwc1-deficient mice and by generating a hippocampus-specific interactome, we show that WWC1 is a major regulatory platform in AMPAR signaling networks. Under basal conditions, the Hippo pathway members WWC1 and large tumor-suppressor kinase (LATS) are associated, which might prevent WWC1 effects on synaptic proteins. Reduction of WWC1/LATS binding through a point mutation at WWC1 elevates the abundance of WWC1 in AMPAR complexes and improves hippocampal-dependent learning and memory. Thus, uncoupling of WWC1 from the Hippo pathway to AMPAR-regulatory complexes provides an innovative strategy to enhance synaptic transmission.

Expression of the Hippo Pathway Core Components in Endometrial Cancer and Its Association with Clinicopathologic Features

BACKGROUND

The Hippo signaling pathway has a key role in tumorigenesis. This study aimed to evaluate the relationship between the expression of core components of the Hippo signaling pathway and its association with clinicopathological features in endometrial cancer.

MATERIALS AND METHODS

We retrospectively collected endometrioid endometrial cancer specimens from 60 patients between January 2002 and December 2009 at Gyeongsang National University Hospital. Relevant clinicopathological data were obtained through electronic medical records of patients. The expression patterns of six core components (YAP, p-YAP, LATS1/2, MST1/2, KIBRA, and Merlin) were identified by immunohistochemistry on tissue microarray sections.

RESULTS

The positive expression ratio was 75.0% for YAP, 73.3% for p-YAP, 26.7% for MST1/2, 16.7% for KIBRA, 15.0% for Merlin, and 15.0% for LATS1/2. YAP expression was negatively correlated with MST 1/2 kinases (p = 0.045) and positively correlated with p-YAP (p = 0.012). Merlin, and MST 1/2 kinases (p = 0.043) showed a positive correlation. A subgroup of patients aged below 60 years (p = 0.004) and with myometrial invasion depth of less than 1/2 (p = 0.041) showed a positive association with YAP expression. p-YAP expression was negatively associated with a subset of patients with primary tumour size ≥4 cm (p = 0.03). Logistic regression analysis showed a significant association between age and YAP expression. The odds ratio of p-YAP expression was significantly lower in the group with tumour size ≥4 cm.

CONCLUSION

Two prognostic factors, age and tumour size, were significantly associated with the expression of YAP and p-YAP in endometrial cancer. Further research should focus on their expression as a marker for prediction of clinicopathological implications in endometrial cancer.

Multiphase coalescence mediates Hippo pathway activation

The function of biomolecular condensates is often restricted by condensate dissolution. Whether condensates can be suppressed without condensate dissolution is unclear. Here, we show that upstream regulators of the Hippo signaling pathway form functionally antagonizing condensates, and their coalescence into a common phase provides a mode of counteracting the function of biomolecular condensates without condensate dissolution. Specifically, the negative regulator SLMAP forms Hippo-inactivating condensates to facilitate pathway inhibition by the STRIPAK complex. In response to cell-cell contact or osmotic stress, the positive regulators AMOT and KIBRA form Hippo-activating condensates to facilitate pathway activation. The functionally antagonizing SLMAP and AMOT/KIBRA condensates further coalesce into a common phase to inhibit STRIPAK function. These findings provide a paradigm for restricting the activity of biomolecular condensates without condensate dissolution, shed light on the molecular principles of multiphase organization, and offer a conceptual framework for understanding upstream regulation of the Hippo signaling pathway.

Pathological Significance and Prognostic Role of WWC1 in Upper Urinary Tract Urothelial Cancer

BACKGROUND/AIM

WW and C2 domain-containing 1 (WWC1) protein is a suppressor of malignancies. However, there is no information on the pathological significance of WWC1 in upper urinary tract cancer (UTUC).

PATIENTS AND METHODS

In this study, WWC1 immunoreactivity was investigated in 152 non-metastatic UTUC samples. The relationships between WWC1 expression and grade, pT stage, proliferative index (using an antibody to Ki-67), and the immunohistochemical expression of matrix metalloproteinase (MMP)-2 and -9 were evaluated.

RESULTS

WWC1 expression was negatively associated with tumor grade and pT stage (p<0.001). Positive expression of WWC1 was a better predictor of the UTUC recurrence and subsequent metastasis, and the multivariate analysis showed that WWC1 expression was a significant predictor of subsequent metastasis (hazard ratio=0.29, p=0.020). WWC1 expression inversely correlated with the proliferative index (odds ratio=2.59, p=0.023) and expression of MMP9 (odds ratio=2.19, p=0.040) but not with MMP2 expression, by multivariate analyses.

CONCLUSION

WWC1 expression was negatively associated with malignant aggressiveness via the suppression of cancer cell proliferation and MMP9 expression in patients with UTUC. This suggests WWC1 to be a useful predictor and novel therapeutic target in patients with UTUC.

Low KIBRA Expression Is Associated with Poor Prognosis in Patients with Triple-Negative Breast Cancer

Background and Objectives: Kidney and brain protein (KIBRA) is a protein encoded by the WW and C2 domain containing 1 (WWC1) gene and is involved in the Hippo signaling pathway. Recent studies have revealed the prognostic value of KIBRA expression; however, its role in breast cancer remains unclear. The aim of this study was to examine KIBRA expression in relation to the clinical and pathological characteristics of patients with breast cancer and to disease outcomes. Materials and Methods: We analyzed the expression of KIBRA and its correlation with event-free survival (EFS) outcomes in resected samples from 486 patients with breast cancer. Results: KIBRA expression was significantly different among the molecular subgroups (low KIBRA expression: luminal A, 46.7% versus 50.0%, p = 0.641; luminal B, 32.7% versus 71.7%, p < 0.001; human epidermal growth factor receptor 2 (HER2)-enriched, 64.9% versus 45.5%. p = 0.001; triple-negative, 73.6% versus 43.8%, p < 0.001). Low KIBRA expression was also associated with high nuclear grade (60.4% versus 37.8%, p < 0.001), high histologic grade (58.7% versus 37.0%, p < 0.001), and estrogen receptor (ER) negativity (54.2% versus 23.6%, p < 0.001). Low KIBRA expression was significantly associated with poor EFS (p = 0.041; hazard ratio (HR) 1.658; 95% confidence interval (CI), 1.015–2.709). Low KIBRA expression was an independent indicator of poor prognosis (p = 0.001; HR = 3.952; 95% CI = 1.542–10.133) in triple-negative breast cancer (TNBC). Conclusion: Low KIBRA expression was associated with higher histological grade, ER negativity and poor EFS of breast cancer. In particular, our data highlight KIBRA expression status as a potential prognostic marker for TNBC.

KIBRA connects Hippo signaling and cancer

The Hippo signaling pathway is a tumor suppressor pathway that plays an important role in tissue homeostasis and organ size control. KIBRA is one of the many upstream regulators of the Hippo pathway. It functions as a tumor suppressor by positively regulating the core Hippo kinase cascade. However, there are accumulating shreds of evidence showing that KIBRA has an oncogenic function, which we speculate may arise from its functions away from the Hippo pathway. In this review, we have attempted to provide an overview of the Hippo signaling with a special emphasis on evidence showing the paradoxical role of KIBRA in cancer.

Interaction of COMT and KIBRA modulates the association between hippocampal structure and episodic memory performance in healthy young adults

Genetic variations of COMT and KIBRA, which were reported to be expressed in the hippocampus, have been linked to memory function. However, their interaction on the hippocampal structure remains unknown. This study aimed to explore the interaction effects of COMT rs4680 and KIBRA rs17070145 on the hippocampal subfield volumes and test their associations with hippocampus-memory relationship in 187 healthy young adults. Two-way analysis of covariance was applied to the alterations in hippocampal subfield volumes among COMT and KIBRA genotypes. Significant interaction effects of these two genes were found in the right CA1 and CA3 subfields. Among KIBRA C-allele carriers, COMT Val/Val homozygotes showed greater volume in these regions than COMT Met-allele carriers. Furthermore, the slope of the correlation between right CA1 volume and immediate recall on the California Verbal Learning Test-II (CVLT-II) (F = 4.36, p = 0.041) as well as CVLT-II delayed recall (F = 6.44, p = 0.014) were significantly different between COMT Val/Val homozygotes and Met-allele carriers, which were positive or tend to be positive in COMT Val/Val group (CVLT immediate recall, r = 0.319, p = 0.040; CVLT delayed recall, r = 0.304, p = 0.051), but absent in COMT Met-allele carriers (CVLT immediate recall, r = -0.263, p = 0.205; CVLT delayed recall, r = -0.351, p = 0.086). These findings may provide a novel insight into the genetic effects upon the hippocampal structure and suggest that the conjoint effects of COMT and KIBRA played a modulatory role in the hippocampus-episodic memory correlation.

Isoform Specificity of PKMs during Long-Term Facilitation in Aplysia Is Mediated through Stabilization by KIBRA

Persistent activity of protein kinase M (PKM), the truncated form of protein kinase C (PKC), can maintain long-term changes in synaptic strength in many systems, including the hermaphrodite marine mollusk, Aplysia californica Moreover, different types of long-term facilitation (LTF) in cultured Aplysia sensorimotor synapses rely on the activities of different PKM isoforms in the presynaptic sensory neuron and postsynaptic motor neuron. When the atypical PKM isoform is required, the kidney and brain expressed adaptor protein (KIBRA) is also required. Here, we explore how this isoform specificity is established. We find that PKM overexpression in the motor neuron, but not the sensory neuron, is sufficient to increase synaptic strength and that this activity is not isoform-specific. KIBRA is not the rate-limiting step in facilitation since overexpression of KIBRA is neither sufficient to increase synaptic strength, nor to prolong a form of PKM-dependent intermediate synaptic facilitation. However, the isoform specificity of dominant-negative-PKMs to erase LTF is correlated with isoform-specific competition for stabilization by KIBRA. We identify a new conserved region of KIBRA. Different splice isoforms in this region stabilize different PKMs based on the isoform-specific sequence of an α-helix "handle" in the PKMs. Thus, specific stabilization of distinct PKMs by different isoforms of KIBRA can explain the isoform specificity of PKMs during LTF in Aplysia SIGNIFICANCE STATEMENT Long-lasting changes in synaptic plasticity associated with memory formation are maintained by persistent protein kinases. We have previously shown in the Aplysia sensorimotor model that distinct isoforms of persistently active protein kinase Cs (PKMs) maintain distinct forms of long-lasting synaptic changes, even when both forms are expressed in the same motor neuron. Here, we show that, while the effects of overexpression of PKMs are not isoform-specific, isoform specificity is defined by a "handle" helix in PKMs that confers stabilization by distinct splice forms in a previously undefined domain of the adaptor protein KIBRA. Thus, we define new regions in both KIBRA and PKMs that define the isoform specificity for maintaining synaptic strength in distinct facilitation paradigms.

KIBRA (WWC1) Is a Metastasis Suppressor Gene Affected by Chromosome 5q Loss in Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBCs) display a complex spectrum of mutations and chromosomal aberrations. Chromosome 5q (5q) loss is detected in up to 70% of TNBCs, but little is known regarding the genetic drivers associated with this event. Here, we show somatic deletion of a region syntenic with human 5q33.2–35.3 in a mouse model of TNBC. Mechanistically, we identify KIBRA as a major factor contributing to the effects of 5q loss on tumor growth and metastatic progression. Re-expression of KIBRA impairs metastasis in vivo and inhibits tumorsphere formation by TNBC cells in vitro. KIBRA functions co-operatively with the protein tyrosine phosphatase PTPN14 to trigger mechanotransduction-regulated signals that inhibit the nuclear localization of oncogenic transcriptional co-activators YAP/TAZ. Our results argue that the selective advantage produced by 5q loss involves reduced dosage of KIBRA, promoting oncogenic functioning of YAP/TAZ in TNBC.

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Reduced KIBRA expression is associated with chr 5q loss in breast cancer

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Restoring Kibra expression inhibits metastatic dissemination in mice

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KIBRA impairs the self-renewal capacity of triple-negative breast cancer cells

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KIBRA blocks mechanotransduction signals required for YAP/TAZ activation

Decoding WW domain tandem-mediated target recognitions in tissue growth and cell polarity

WW domain tandem-containing proteins such as KIBRA, YAP, and MAGI play critical roles in cell growth and polarity via binding to and positioning target proteins in specific subcellular regions. An immense disparity exists between promiscuity of WW domain-mediated target bindings and specific roles of WW domain proteins in cell growth regulation. Here, we discovered that WW domain tandems of KIBRA and MAGI, but not YAP, bind to specific target proteins with extremely high affinity and exquisite sequence specificity. Via systematic structural biology and biochemistry approaches, we decoded the target binding rules of WW domain tandems from cell growth regulatory proteins and uncovered a list of previously unknown WW tandem binding proteins including β-Dystroglycan, JCAD, and PTPN21. The WW tandem-mediated target recognition mechanisms elucidated here can guide functional studies of WW domain proteins in cell growth and polarity as well as in other cellular processes including neuronal synaptic signaling.

The Neuroprotection of KIBRA in Promoting Neuron Survival and Against Amyloid β-Induced Apoptosis

Background: Recent research has identified the nucleotide polymorphisms of KIdney and BRAin expressed protein (KIBRA) to be associated with cognitive performance, suggesting its vital role in Alzheimer’s disease (AD); however, the underlying molecular mechanism of KIBRA in AD remains obscure.

Methods: The AD animal model (APP/PS1 transgenic mice) and KIBRA knockout (KIBRA KO) mice were used to investigate pathophysiological changes of KIBRA in vivo. Mouse hippocampal cell line (HT22) was used to explore its molecular mechanism through KIBRA CRISPR/Cas9-sgRNA system and KIBRA overexpression lentivirus in vitro.

Results: Aged APP/PS1 mice displayed increased neuronal apoptosis in the hippocampus, as did KIBRA KO mice. KIBRA deficiency was closely related to neuronal loss in the brain. In addition, knockdown of KIBRA in neuronal cell lines suppressed its growth and elevated apoptosis-associated protein levels under the stress of Aβ_1–42 oligomers. On the contrary, overexpression of KIBRA significantly promoted cell proliferation and reduced its apoptosis. Moreover, through screening several survival-related signaling pathways, we found that KIBRA inhibited apoptosis by activating the Akt pathway other than ERK or PKC pathways, which was further confirmed by Akt-specific inhibitor MK2206.

Conclusion: Our data indicate that KIBRA may function as a neuroprotective gene in promoting neuron survival and inhibiting Aβ-induced neuronal apoptosis.

KIBRA T allele influences memory performance and progression of cognitive decline: a 7-year follow-up study in subjective cognitive decline and mild cognitive impairment

KIBRA is a signal transducer protein, mainly expressed in the kidney and brain. A single-nucleotide polymorphism (SNP rs17070145, T → C exchange) has been linked to different cognitive function. In 2008, we studied 70 subjects who complained of subjective cognitive decline (SCD) and found that CT/TT carriers performed worse than CC carriers on a long-term memory test. We followed up the 70 SCD subjects and also 31 subjects affected by mild cognitive impairment (MCI) for a mean follow-up time of 7 years, during which 16 SCD subjects progressed to MCI and 14 MCI subjects progressed to Alzheimer's disease (AD). Carrying the T allele was associated with MCI and with a two times-higher risk of developing MCI than CC carriers. In the SCD sample, CT/TT carriers showed a greater worsening on Rivermead Behavioral Memory Test (RBMT) compared to CC carriers. In the MCI sample, CT/TT carriers performed worse than CC carriers on RBMT. There is a lack of consensus on the effect of KIBRA gene variants on cognitive performances in episodic memory and on the risk of AD. Our results confirm a role of T allele on progression of cognitive decline.

KIBRA polymorphism modulates gray matter volume to influence cognitive ability in the elderly

Genetic variation in the kidney and brain expressed protein (KIBRA) rs17070145 gene has been linked to episodic memory and cognitive aging; yet, the neural mechanism underlying this association remains to be fully understood. Using the magnetic resonance imaging (MRI) technique, this study investigated the effect of KIBRA polymorphism on gray matter volume in 37 healthy, Chinese adults from the older population. Voxel-based morphometry (VBM) analysis revealed that KIBRA gene selectivity influences the prefrontal cortex and the parahippocampal cortex. The gray matter volume (GMV) in these structures is significantly lower in KIBRA C-allele carriers than in TT carriers. Moreover, multi-voxel pattern correlation analysis revealed that decreased prefrontal GMV could in turn affect individual cognitive function in C-allele carriers; whereas, TT individuals utilized more integrated gray matter volume in whole-brain voxels to achieve relatively better cognitive function. Overall, the findings suggest that the KIBRA rs17070145 polymorphism modulates gray matter volume, which in turn further influences cognitive function in the elderly.

Distinctive phosphoinositide- and Ca2+-binding properties of normal and cognitive performance-linked variant forms of KIBRA C2 domain

Kidney- and brain-expressed protein (KIBRA), a multifunctional scaffold protein with around 20 known binding partners, is involved in memory and cognition, organ size control via the Hippo pathway, cell polarity, and membrane trafficking. KIBRA includes tandem N-terminal WW domains, a C2 domain, and motifs for binding atypical PKC and PDZ domains. A naturally occurring human KIBRA variant involving residue changes at positions 734 (Met-to-Ile) and 735 (Ser-to-Ala) within the C2 domain affects cognitive performance. We have elucidated 3D structures and calcium- and phosphoinositide-binding properties of human KIBRA C2 domain. Both WT and variant C2 adopt a canonical type I topology C2 domain fold. Neither Ca²⁺ nor any other metal ion was bound to WT or variant KIBRA C2 in crystal structures, and Ca²⁺ titration produced no significant reproducible changes in NMR spectra. NMR and X-ray diffraction data indicate that KIBRA C2 binds phosphoinositides via an atypical site involving β-strands 5, 2, 1, and 8. Molecular dynamics simulations indicate that KIBRA C2 interacts with membranes via primary and secondary sites on the same domain face as the experimentally identified phosphoinositide-binding site. Our results indicate that KIBRA C2 domain association with membranes is calcium-independent and involves distinctive C2 domain-membrane relative orientations.

KIBRA; a novel biomarker predicting recurrence free survival of breast cancer patients receiving adjuvant therapy

BACKGROUND

This study was carried out to evaluate the prognostic value of KIBRA in breast cancer.

METHODS

This retrospective study included breast cancer patients who sought the services of the immunohistochemistry laboratory of our unit from 2006 to 2015. Tissue microarrays were constructed and immunohistochemical staining was done to assess the KIBRA expression. The Kaplan-Meier model for univariate and Cox-regression model with backward stepwise factor retention method for multivariate analyses were used. Chi square test was used to find out the associations with the established prognostic features.

RESULTS

A total of 1124 patients were included in the study and KIBRA staining of 909 breast cancers were available for analysis. Cytoplasmic KIBRA expression was seen in 39.5% and nuclear expression in 44.8%. Overall KIBRA-low breast cancers accounted for 41.5%. KIBRA nuclear expression was significantly associated with positive ER and PR expression. Luminal breast cancer patients who had endocrine therapy and KIBRA-low expression had a RFS disadvantage over those who were positive for KIBRA (p = 0.02). Similarly, patients who received chemotherapy and had overall KIBRA-low expression also demonstrated a RFS disadvantage compared to those who had overall positive KIBRA expression (p = 0.018). This effect of KIBRA was independent of the other factors considered for the model.

CONCLUSION

Overall low-KIBRA expression has an independent effect on the RFS and predicts the RFS outcome of luminal breast cancer patients who received endocrine therapy and breast cancer patients who received chemotherapy.

The role of KIBRA in reconstructive episodic memory

BACKGROUND

In order to retrieve episodic past events, the missing information needs to be reconstructed using information stored in semantic memory. Failures in these reconstructive processes are expressed as false memories. KIBRA single nucleotide polymorphism (rs17070145) has been linked to episodic memory performance as well as an increased risk of Alzheimer's disease and post-traumatic stress disorder (PTSD).

METHODS

Here, the role of KIBRA rs17070145 polymorphism (male and female CC vs. CT/TT carriers) in reconstructive episodic memory in the Deese-Roediger-McDermott (DRM) paradigm was investigated in N = 219 healthy individuals.

RESULTS

Female participants outperformed males in the free recall condition. Furthermore, a trend towards a gender x genotype interaction was found for false recognition rates. Female CT/TT carriers exhibited a lower proportion of false recognition rates for associated critical lures as compared to male CT/TT. Additionally, an association between KIBRA rs17070145 genotype, familiarity and recollection based recognition performance was found. In trials with correct recognition of listed items CT/TT carriers showed more "remember", but fewer "know" responses as compared to CC carriers.

DISCUSSION AND CONCLUSION

Our findings suggest that the T-allele of KIBRA rs17070145 supports recollection based episodic memory retrieval and contributes to memory accuracy in a gender dependent manner. Findings are discussed in the context of the specific contribution of KIBRA related SNPs to reconstructive episodic memory and its implications for cognitive and emotional symptoms in dementia and PTSD.

Age-Modulated Associations between KIBRA, Brain Volume, and Verbal Memory among Healthy Older Adults

The resource modulation hypothesis suggests that the influence of genes on cognitive functioning increases with age. The KIBRA single nucleotide polymorphism rs17070145, associated with episodic memory and working memory, has been suggested to follow such a pattern, but few studies have tested this assertion directly. The present study investigated the relationship between KIBRA alleles (T carriers vs. CC homozygotes), cognitive performance, and brain volumes in three groups of cognitively healthy adults-middle aged (ages 52-64, n = 38), young old (ages 65-72, n = 45), and older old (ages 73-92, n = 62)-who were carefully matched on potentially confounding variables including apolipoprotein ε4 status and hypertension. Consistent with our prediction, T carriers maintained verbal memory performance with increasing age while CC homozygotes declined. Voxel-based morphometric analysis of magnetic resonance images showed an advantage for T carriers in frontal white matter volume that increased with age. Focusing on the older old group, this advantage for T carriers was also evident in left lingual gyrus gray matter and several additional frontal white matter regions. Contrary to expectations, neither KIBRA nor the interaction between KIBRA and age predicted hippocampal volumes. None of the brain regions investigated showed a CC homozygote advantage. Taken together, these data suggest that KIBRA results in decreased verbal memory performance and lower brain volumes in CC homozygotes compared to T carriers, particularly among the oldest old, consistent with the resource modulation hypothesis.

No differences in brain microstructure between young KIBRA-C carriers and non-carriers

KIBRA rs17070145 polymorphism is associated with variations in memory function and the microstructure of related brain areas. Diffusion kurtosis imaging (DKI) as an extension of diffusion tensor imaging that can provide more information about changes in microstructure, based on the idea that water diffusion in biological tissues is heterogeneous due to structural hindrance and restriction. We used DKI to explore the relationship between KIBRA gene polymorphism and brain microstructure in young adults. We recruited 100 healthy young volunteers, including 53 TT carriers and 47 C allele carriers. No differences were detected between the TT homozygotes and C-allele carriers for any diffusion and kurtosis parameter. These results indicate KIBRA rs17070145 polymorphism likely has little or no effect on brain microstructure in young adults.

Hippo Signaling: Emerging Pathway in Stress-Related Psychiatric Disorders?

Discovery of the Hippo pathway and its core components has made a significant impact on our progress in the understanding of organ development, tissue homeostasis, and regeneration. Upon diverse extracellular and intracellular stimuli, Hippo signaling regulates stemness, cell proliferation and apoptosis by a well-conserved signaling cascade, and disruption of these systems has been implicated in cancer as well as metabolic and neurodegenerative diseases. The central role of Hippo signaling in cell biology also results in prominent links to stress-regulated pathways. Genetic variations, epigenetically provoked upregulation of Hippo pathway members and dysregulation of cellular processes implicated in learning and memory, are linked to an increased risk of stress-related psychiatric disorders (SRPDs). In this review, we summarize recent findings, supporting the role of Hippo signaling in SRPDs by canonical and non-canonical Hippo pathway interactions.

Bad Ac-etylated Tau

By using a tau construct with two mimicked acetylation sites as identified in AD brains, Tracy et al. (2016) found that acetylated tau promotes synaptic dysfunction through disruption of postsynaptic KIBRA signaling pathways, actin dynamics, and AMPA receptor trafficking.

Elevated expression of Par3 promotes prostate cancer metastasis by forming a Par3/aPKC/KIBRA complex and inactivating the hippo pathway

Background

Prostate cancer (PCa) is one of the most frequent tumors and leading cause of cancer deaths among males worldwide. The majority of deaths are due to recurrence and subsequent development of the metastatic cancer. Although loss or dislocalization of polarity proteins has been implicated in embryogenesis deficiency and tumorigenesis, association of polarity protein expression levels with tumor metastasis remains unclear.

Methods

Bioinformatics, qRT-PCR, western blot and immunohistochemical (IHC) analyses were used to examine expression of Par3, a key component of polarity-associated partitioning defective (PAR) complex, in primary and metastatic clinical PCa samples. Loss-of-function and gain-of-function studies in vitro and in vivo were performed to determine the functions of Par3 during metastasis of PCa. Co-immunoprecipitation (co-IP), western blot, immunofluorescence (IF), chromatin immunoprecipitation (ChIP) and qRT-PCR analyses were conducted to investigate the underlying mechanism for the function of Par3 on PCa metastasis.

Results

In this study, we found that elevated expression of Par3 is positively associated with PCa metastasis. Knockdown of Par3 inhibits PCa cell migration and invasion in vitro and tumor metastasis in vivo, whereas overexpression of Par3 yields the opposite results. Mechanistically, Par3 suppresses phosphorylation of LATS to inactivate the Hippo pathway and enhances nuclear translocation of YAP by sequestrating KIBRA from the KIBRA/Merlin/FRMD6 complex and forming a Par3/aPKC/KIBRA complex. Stable knockdown of Par3 leads to restoration of the KIBRA/Merlin/FRMD6 complex and activation of the Hippo pathway, and then results in an inhibition on YAP nuclear translocation. In addition, in conjunction with the TEA domain (TEAD) transcription factor family, intranuclear YAP promotes the transcription of several pro-metastatic genes such as the matrix metalloproteinase (MMP) family, Zeb1, Snail1 and Twist1. Moreover, knockdown of Par3 downregulates expression of these pro-metastatic genes.

Conclusions

Our findings indicate that elevated expression of Par3 promotes PCa metastasis via KIBRA sequestration-mediated inactivation of the Hippo pathway to upregulate expression of pro-metastatic genes. Downregulation of Par3 expression may serve as a potential treatment approach for PCa metastasis by activating the Hippo pathway.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0609-y) contains supplementary material, which is available to authorized users.

Aging and a genetic KIBRA polymorphism interactively affect feedback- and observation-based probabilistic classification learning

Probabilistic category learning involves complex interactions between the hippocampus and striatum that may depend on whether acquisition occurs via feedback or observation. Little is known about how healthy aging affects these processes. We tested whether age-related behavioral differences in probabilistic category learning from feedback or observation depend on a genetic factor known to influence individual differences in hippocampal function, the KIBRA gene (single nucleotide polymorphism rs17070145). Results showed comparable age-related performance impairments in observational as well as feedback-based learning. Moreover, genetic analyses indicated an age-related interactive effect of KIBRA on learning: among older adults, the beneficial T-allele was positively associated with learning from feedback, but negatively with learning from observation. In younger adults, no effects of KIBRA were found. Our results add behavioral genetic evidence to emerging data showing age-related differences in how neural resources relate to memory functions, namely that hippocampal and striatal contributions to probabilistic category learning may vary with age. Our findings highlight the effects genetic factors can have on differential age-related decline of different memory functions.

Selective Erasure of Distinct Forms of Long-Term Synaptic Plasticity Underlying Different Forms of Memory in the Same Postsynaptic Neuron

Generalization of fear responses to non-threatening stimuli is a feature of anxiety disorders. It has been challenging to target maladaptive generalized memories without affecting adaptive memories. Synapse-specific long-term plasticity underlying memory involves the targeting of plasticity-related proteins (PRPs) to activated synapses. If distinct tags and PRPs are used for different forms of plasticity, one could selectively remove distinct forms of memory. Using a stimulation paradigm in which associative long-term facilitation (LTF) occurs at one input and non-associative LTF at another input to the same postsynaptic neuron in an Aplysia sensorimotor preparation, we found that each form of LTF is reversed by inhibiting distinct isoforms of protein kinase M (PKM), putative PRPs, in the postsynaptic neuron. A dominant-negative (dn) atypical PKM selectively reversed associative LTF, while a dn classical PKM selectively reversed non-associative LTF. Although both PKMs are formed from calpain-mediated cleavage of protein kinase C (PKC) isoforms, each form of LTF is sensitive to a distinct dn calpain expressed in the postsynaptic neuron. Associative LTF is blocked by dn classical calpain, whereas non-associative LTF is blocked by dn small optic lobe (SOL) calpain. Interfering with a putative synaptic tag, the adaptor protein KIBRA, which protects the atypical PKM from degradation, selectively erases associative LTF. Thus, the activity of distinct PRPs and tags in a postsynaptic neuron contribute to the maintenance of different forms of synaptic plasticity at separate inputs, allowing for selective reversal of synaptic plasticity and providing a cellular basis for developing therapeutic strategies for selectively reversing maladaptive memories.

Acetylated tau in Alzheimer's disease: An instigator of synaptic dysfunction underlying memory loss: Increased levels of acetylated tau blocks the postsynaptic signaling required for plasticity and promotes memory deficits associated with tauopathy

Pathogenesis in tauopathies involves the accumulation of tau in the brain and progressive synapse loss accompanied by cognitive decline. Pathological tau is found at synapses, and it promotes synaptic dysfunction and memory deficits. The specific role of toxic tau in disrupting the molecular networks that regulate synaptic strength has been elusive. A novel mechanistic link between tau toxicity and synaptic plasticity involves the acetylation of two lysines on tau, K274, and K281, which are associated with dementia in Alzheimer's disease (AD). We propose that an increase in tau acetylated on these lysines blocks the expression of long-term potentiation at hippocampal synapses leading to impaired memory in AD. Acetylated tau could inhibit the activity-dependent recruitment of postsynaptic AMPA-type glutamate receptors required for plasticity by interfering with the postsynaptic localization of KIBRA, a memory-associated protein. Strategies that reduce the acetylation of tau may lead to effective treatments for cognitive decline in AD.

The Regulatory Role of KIBRA and PTPN14 in Hippo Signaling and Beyond

The Hippo signaling pathway regulates cellular proliferation and survival, thus exerting profound effects on normal cell fate and tumorigenesis. Pivotal effectors of this pathway are YAP/TAZ, transcriptional co-activators whose dysfunction contributes to the development of cancer. Complex networks of intracellular and extracellular signaling pathways that modulate YAP and TAZ activities have recently been identified. Among them, KIBRA and PTPN14 are two evolutionarily-conserved and important YAP/TAZ upstream regulators. They can negatively regulate YAP/TAZ functions separately or in concert. In this review, we summarize the current and emerging regulatory roles of KIBRA and PTPN14 in the Hippo pathway and their functions in cancer.

KIBRA promotes prostate cancer cell proliferation and motility

KIBRA is a regulator of the Hippo-yes-associated protein (YAP) pathway, which plays a critical role in tumorigenesis. In the present study, we show that KIBRA is a positive regulator in prostate cancer cell proliferation and motility. We found that KIBRA is transcriptionally upregulated in androgen-insensitive LNCaPC4-2 and LNCaP-C81 cells compared to parental androgen-sensitive LNCaP cells. Ectopic expression of KIBRA enhances cell proliferation, migration and invasion in both immortalized and cancerous prostate epithelial cells. Accordingly, knockdown of KIBRA reduces migration, invasion and anchorage-independent growth in LNCaP-C4-2/C81 cells. Moreover, KIBRA expression is induced by androgen signaling and KIBRA is partially required for androgen receptor signaling activation in prostate cancer cells. In line with these findings, we further show that KIBRA is overexpressed in human prostate tumors. Our studies uncover unexpected results and identify KIBRA as a tumor promoter in prostate cancer.

Investigating the influence of KIBRA and CLSTN2 genetic polymorphisms on cross-sectional and longitudinal measures of memory performance and hippocampal volume in older individuals

The variability of episodic memory decline and hippocampal atrophy observed with increasing age may partly be explained by genetic factors. KIBRA (kidney and brain expressed protein) and CLSTN2 (calsyntenin 2) are two candidate genes previously linked to episodic memory performance and volume of the hippocampus, a key memory structure. However, whether polymorphisms in these two genes also influence age-related longitudinal memory decline and hippocampal atrophy is still unknown. Using data from two independent cohorts, the Sydney Memory and Ageing Study and the Older Australian Twins Study, we investigated whether the KIBRA and CLSTN2 genetic polymorphisms (rs17070145 and rs6439886) are associated with episodic memory performance and hippocampal volume in older adults (65-90 years at baseline). We were able to examine these polymorphisms in relation to memory and hippocampal volume using cross-sectional data and, more importantly, also using longitudinal data (2 years between testing occasions). Overall we did not find support for an association of KIBRA either alone or in combination with CLSTN2 with memory performance or hippocampal volume, nor did variation in these genes influence longitudinal memory decline or hippocampal atrophy in two cohorts of older adults.

Association of KIBRA rs17070145 polymorphism with episodic memory in the early stages of a human neurodevelopmental disorder

A common T/C polymorphism within the ninth intron of the KIBRA gene (rs17070145) is thought to influence memory in humans. Since cognitive impairment, including memory, is a core feature of schizophrenia, we attempted to investigate this association in an independent sample of adolescent patients with early-onset schizophrenia (EOS; onset before age 18) probands and their healthy siblings. In a sample of 25 pairs of EOS proband-healthy full sibling, we sought to investigate the association of KIBRA with memory performance. Episodic memory was measured using immediate and delayed recall measures of the California Verbal Learning Test. EOS underperformed at immediate and delayed recall compared with siblings. In a combined analysis (TT vs. TC/CC) assuming a C dominant model of inheritance, we found a main effect of genotype where individuals with TT genotype outperformed non-TT-carriers at immediate and delayed recall. A genotype by group interaction showed that EOS with TT genotype did not show a memory advantage over siblings with TT or non-TT-carriers at immediate or delayed recall. Siblings with TT genotype showed enhanced immediate recall (not delayed recall) compared with non-TT-carriers. This study demonstrates an association between the KIBRA gene and episodic memory (immediate free recall) and suggests a differential effect of this genetic variant in EOS and healthy siblings.

KIBRA gene polymorphism has no association with verbal or visual episodic memory performance

Inter-individual variability in memory performance has been suggested to result, in part, from genetic differences in the coding of proteins involved in long-term potentiation (LTP). The present study examined the effect of a single-nucleotide polymorphism (SNP) in the KIBRA gene (rs17070145) on episodic memory performance, using multiple measures of verbal and visual episodic memory. A total of 256 female and 130 male healthy, older adults (mean age = 60.86 years) were recruited from the Tasmanian Healthy Brain Project (THBP), undergoing both neuropsychological and genetic testing. The current study showed no significant effect of the KIBRA polymorphism on performance on the Rey Auditory Verbal Learning Task, Logical Memory test, Paired Associates Learning test or Rey Complex Figure Task. The results suggest there is little to no functional significance of KIBRA genotype on episodic memory performance, regardless of modality.

Interactive effects of KIBRA and CLSTN2 polymorphisms on episodic memory in old-age unipolar depression

The KIBRA (rs17070145) C-allele and the CLSTN2 (rs6439886) T-allele have both been associated with poorer episodic memory performance. Given that episodic memory is affected in depression, we hypothesized that the combination of these risk alleles would be particularly detrimental to episodic memory performance in depressed persons. In the population-based SNAC-K study, 2170 participants (≥ 60 years) without dementia (DSM-IV criteria) and antidepressant pharmacotherapy were clinically examined and diagnosed following ICD-10 criteria for unipolar depression, and genotyped for KIBRA and CLSTN2. Participants were categorized according to unipolar depression status (yes, no) and genotype combinations (KIBRA: CC, any T; CLSTN2: TT, any C). Critically, a three-way interaction effect showed that the CC/TT genotype combination was associated with poorer episodic recall and recognition performance only in depressed elderly persons, with depressed CC/TT carriers consistently performing at the lowest level. This finding supports the view that effects of genetic polymorphisms on cognitive functioning may be most easily disclosed at suboptimal levels of cognitive ability, such as in old-age depression.

Effects of the KIBRA Single Nucleotide Polymorphism on Synaptic Plasticity and Memory: A Review of the Literature

There has been a great deal of interest recently in genetic effects on neurocognitive performance in the healthy population. KIBRA –a postsynaptic protein from the WWC family of proteins– was identified in 2003 in the human brain and kidney and has recently been associated with memory performance and synaptic plasticity. Through genome-wide screening, a single nucleotide polymorphism (SNP) was detected in the ninth intron of KIBRA gene (T→ C substitution) and was implicated in human memory and the underlying neuronal circuitry. This review presents a synopsis of the current findings on the effects of the KIBRA SNP on human memory and synaptic plasticity. Overall the findings suggest impaired memory performance and less efficient or impaired hippocampal/medial temporal lobe (MTL) activation in CC homozygotes (in comparison to T carriers) with some differences between young and older subjects. This review also highlights limitations and potential sources for variability of studies’ imaging findings along with future perspectives and implications for the role of KIBRA in memory-related brain systems.

WWC1 genotype modulates age-related decline in episodic memory function across the adult life span

BACKGROUND

Episodic memory (EM) declines with age and the rate of decline is variable across individuals. A single nucleotide polymorphism (rs17070145) in the WWC1 gene that encodes the KIBRA protein critical for long-term potentiation and memory consolidation has previously been associated with EM performance, as well as differences in hippocampal engagement during EM tasks using functional magnetic resonance imaging (fMRI). In the current study, we explore the effect of this polymorphism on EM-related activity and cognitive performance across the adult life span using fMRI.

METHODS

Two hundred thirty-two healthy, Caucasian subjects (18-89 years) completed a battery of cognitive tests, as well as an EM task during an fMRI scan.

RESULTS

WWC1 T carriers had significantly better delayed recall performance than CC individuals (p = .006). The relationship between increasing age and recall scores (immediate and delayed) was also significantly different between WWC1 genotype groups (p = .01). In addition to the age-related decline in hippocampal formation (HF) activation (p < .05; false discovery ratesmall volume correction-HF-region of interest), we observed an age by WWC1 genotype interaction on HF activation during encoding and retrieval. The CC group showed a significant negative association between HF activity and increasing age, while no such association was observed in the T carrier group (left HF p = .04; r-z correlation difference during encoding and retrieval; right HF p = .0008; r-z correlation difference during retrieval).

CONCLUSIONS

Our results show a dynamic relationship between rs17070145 polymorphism and increasing age on neuronal activity in the hippocampal region.

KIBRA: In the brain and beyond

In mammals, the KIBRA locus has been associated with memory performance and cognition by genome-wide single nucleotide polymorphism screening. Genetic studies in Drosophila and human cells have identified KIBRA as a novel regulator of the Hippo signaling pathway, which plays a critical role in human tumorigenesis. Recent studies also indicated that KIBRA is involved in other physiological processes including cell polarity, membrane/vesicular trafficking, mitosis and cell migration. At the biochemical level, KIBRA protein is highly phosphorylated by various kinases in epithelial cells. Here, we discuss the updates concerning the function and regulation of KIBRA in the brain and beyond.

Phosphorylation of KIBRA by the extracellular signal-regulated kinase (ERK)-ribosomal S6 kinase (RSK) cascade modulates cell proliferation and migration

In mammals, KIBRA is defined as a memory performance-associated protein. The physiological function and regulation of KIBRA in non-neuronal cells are much less understood. Recent studies have identified KIBRA as a novel regulator of the Hippo signaling pathway, which plays a critical role in tumorigenesis by inhibiting cell proliferation and promoting apoptosis. We recently reported that KIBRA is phosphorylated by the mitotic kinases Aurora and cyclin-dependent kinase 1 during mitosis. In this current study, we show that KIBRA is also phosphorylated by the ERK (extracellular signal-regulated kinases)-RSK (p90 ribosomal S6 kinases) cascade. We demonstrated that ERK1/2 phosphorylate KIBRA at Ser(548) in cells as well as in vitro. Moreover, we found that RSK1/2 specifically phosphorylates KIBRA at two highly conserved sites (Thr(929) and Ser(947)) in vitro and in cells. RSK-mediated phosphorylation is required for KIBRA binding to RSK1, but not RSK2. Surprisingly, KIBRA knockdown impaired cell migration and proliferation in breast cancer cells. By using inducible-expression cell lines, we further show that phospho-regulation of KIBRA by ERK1/2 and RSK1/2 is required for proper cell proliferation and RSK-mediated phosphorylation also modulates KIBRA's migratory activity in MDA-MB-231 breast cancer cells. Our findings uncover unexpected results and a new mechanism through which KIBRA regulates cell migration and proliferation.

The role of memory-related gene WWC1 (KIBRA) in lifetime posttraumatic stress disorder: evidence from two independent samples from African conflict regions

BACKGROUND

Posttraumatic stress disorder (PTSD) results from the formation of a strong memory for the sensory-perceptual and affective representations of traumatic experiences, which is detached from the corresponding autobiographical context information. Because WWC1, the gene encoding protein KIBRA, is associated with long-term memory performance, we hypothesized that common WWC1 alleles influence the risk for a lifetime diagnosis of PTSD.

METHODS

Traumatic load and diagnosis of current and lifetime PTSD were assessed in two independent African samples of survivors from conflict zones who had faced severe trauma (n = 392, Rwanda, and n = 399, Northern Uganda, respectively). Array-based single nucleotide polymorphism (SNP) genotyping was performed. The influence of WWC1 tagging SNPs and traumatic load on lifetime PTSD was estimated by means of logistic regression models with correction for multiple comparisons in the Rwandan sample. Replication analysis was performed in the independent Ugandan sample.

RESULTS

An association of two neighboring SNPs in almost complete linkage disequilibrium, rs10038727 and rs4576167, with lifetime PTSD was discovered in the Rwandan sample. Although each traumatic event added to the probability of lifetime PTSD in a dose-dependent manner in both genotype groups, carriers of the minor allele of both SNPs displayed a diminished risk (p = .007, odds ratio = .29 [95% confidence interval = .15-.54]). This effect was confirmed in the independent Ugandan sample.

CONCLUSIONS

This study reveals an association between two WWC1 SNPs and the likelihood of PTSD development, indicating that this memory-related gene might be involved in processes that occur in response to traumatic stress and influence the strengthening of fear memories.

The KIBRA-aPKC connection: A potential regulator of membrane trafficking and cell polarity

The kidney and brain protein (KIBRA) is a scaffold or an adaptor-like protein with WW, C2-like and atypical protein kinase C (aPKC)-binding domains. Genetic studies in Drosophila revealed that KIBRA is an upstream regulator of the conserved Hippo pathway, which is implicated in organ size determination. In addition, genome-wide studies revealed an association between the single nucleotide polymorphism in the KIBRA gene locus and human episodic memory performance. However, the mechanism of action through which KIBRA is linked to these functions remains poorly understood. Recent studies on the biochemical and cellular properties of KIBRA reveal the role of KIBRA as a regulator of membrane trafficking. Further, KIBRA directly inhibits the activity of the cell polarity regulator, aPKC, which is required for apical protein exocytosis. Here, we discuss how this KIBRA-aPKC connection, a potential regulator of membrane trafficking and cell polarity, can contribute to the recently discovered functions of KIBRA.