Dynein and muskelin control myosin VI delivery towards the neuronal nucleus

A comprehensive analysis of MYO6 as a promising biomarker for diagnosis, prognosis, and immunity in clear cell renal cell carcinoma

Background

Clear cell renal cell carcinoma (ccRCC) is the most common type of renal cell carcinoma. The myosin 6 (MYO6) plays an important role in tumorigenesis and progression. However, its prognostic and immunological effects in ccRCC have not been comprehensively and systematically studied. Therefore, this study aimed to investigate the prognostic value and immune-related role of MYO6 in ccRCC.

Methods

The expression of MYO6 mRNA and protein in normal and tumor tissues using The Cancer Genome Atlas (TCGA) and other public databases were analyzed. In order to further improve the accuracy of the results, immunohistochemistry (IHC) was performed to verify the results. R software, an integrated repository portal for tumor-immune system interactions (TISIDB) and other online analysis tools were used to investigate the relationship between MYO6 expression and clinicopathological features, diagnostic and prognostic value, and the level of immune infiltration in patients with ccRCC. MYO6 genomic alterations were then investigated using the cBio Cancer Genomics Portal (cBioPortal) database. Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and Gene Set Enrichment Analysis (GSEA) enrichment analysis were used to elucidate the biological processes and signaling pathways. Finally, a protein interaction network was constructed using Biological Universal Repository for Interactive Datasets (BioGRID) and some online analysis tools to investigate the correlation between MYO6 and its co-expressed genes in ccRCC patients.

Results

In the present study, MYO6 expression was significantly reduced in ccRCC tumors compared with normal tissues.This was consistent with the results of immunohistochemistry. Lower MYO6 expression levels were significantly associated with higher cancer grade and later TNM stage in ccRCC. Compared with the MYO6 high expression group, ccRCC patients with low MYO6 expression had a poor prognosis of overall survival (OS). MYO6 expression has diagnostic and prognostic potential in ccRCC. MYO6 expression is associated with different tumor-infiltrating immune cells, especially macrophages.

Conclusions

The findings suggest that reduced MYO6 expression levels are associated with disease progression, poor prognosis, and immune cell infiltration, and can be considered as a promising prognostic biomarker for ccRCC.

Myosin in chromosome organisation and gene expression

The importance of myosin motor protein is well-characterised within the cytoplasm and cytoskeleton. However, mounting evidence on four nuclear myosins highlights the central role these proteins have in maintaining genomic stability and gene expression. This review focuses on each of their critical roles in chromatin structure, chromosome translocation, transcription regulation, and DNA damage repair in terms of maintaining chromosome and chromatin integrity.

Tubb3 expression levels are sensitive to neuronal activity changes and determine microtubule growth and kinesin-mediated transport

Microtubules are dynamic polymers of α/β-tubulin. They regulate cell structure, cell division, cell migration, and intracellular transport. However, functional contributions of individual tubulin isotypes are incompletely understood. The neuron-specific β-tubulin Tubb3 displays highest expression around early postnatal periods characterized by exuberant synaptogenesis. Although Tubb3 mutations are associated with neuronal disease, including abnormal inhibitory transmission and seizure activity in patients, molecular consequences of altered Tubb3 levels are largely unknown. Likewise, it is unclear whether neuronal activity triggers Tubb3 expression changes in neurons. In this study, we initially asked whether chemical protocols to induce long-term potentiation (cLTP) affect microtubule growth and the expression of individual tubulin isotypes. We found that growing microtubules and Tubb3 expression are sensitive to changes in neuronal activity and asked for consequences of Tubb3 downregulation in neurons. Our data revealed that reduced Tubb3 levels accelerated microtubule growth in axons and dendrites. Remarkably, Tubb3 knockdown induced a specific upregulation of Tubb4 gene expression, without changing other tubulin isotypes. We further found that Tubb3 downregulation reduces tubulin polyglutamylation, increases KIF5C motility and boosts the transport of its synaptic cargo N-Cadherin, which is known to regulate synaptogenesis and long-term potentiation. Due to the large number of tubulin isotypes, we developed and applied a computational model based on a Monte Carlo simulation to understand consequences of tubulin expression changes in silico. Together, our data suggest a feedback mechanism with neuronal activity regulating tubulin expression and consequently microtubule dynamics underlying the delivery of synaptic cargoes.

Muskelin regulates actin-dependent synaptic changes and intrinsic brain activity relevant to behavioral and cognitive processes

Muskelin (Mkln1) is implicated in neuronal function, regulating plasma membrane receptor trafficking. However, its influence on intrinsic brain activity and corresponding behavioral processes remains unclear. Here we show that murine Mkln1 knockout causes non-habituating locomotor activity, increased exploratory drive, and decreased locomotor response to amphetamine. Muskelin deficiency impairs social novelty detection while promoting the retention of spatial reference memory and fear extinction recall. This is strongly mirrored in either weaker or stronger resting-state functional connectivity between critical circuits mediating locomotor exploration and cognition. We show that Mkln1 deletion alters dendrite branching and spine structure, coinciding with enhanced AMPAR-mediated synaptic transmission but selective impairment in synaptic potentiation maintenance. We identify muskelin at excitatory synapses and highlight its role in regulating dendritic spine actin stability. Our findings point to aberrant spine actin modulation and changes in glutamatergic synaptic function as critical mechanisms that contribute to the neurobehavioral phenotype arising from Mkln1 ablation.

A murine muskelin knockout induces increased exploratory drive and alters cognition and functional connectivity. These effects correlate with actin-dependent changes in dendritic branching, spine structure, and AMPAR-mediated synaptic transmission.