Endocytic trafficking factor VPS45 is essential for spatial regulation of lens fiber differentiation in zebrafish

VPS45 Contributes to the Progression of Hepatocellular Carcinoma by Triggering the Wnt/β-Catenin Signaling Pathway

Vacuolar protein sorting 45 (VPS45) has recently been implicated in the development of ovarian cancer and non-small cell lung cancer. However, its role in the onset and progression of hepatocellular carcinoma (HCC) remains unclear. This study aims to elucidate the function of VPS45 in HCC. Bioassays were conducted to assess the prognostic significance of VPS45 in HCC. Techniques such as western blotting and real-time quantitative polymerase chain reaction (qRT-PCR) were used to confirm the expression levels of VPS45 in HCC tissues and cell lines, as well as to evaluate the expression of downstream effectors in its potential tumorigenic pathways. The impact of VPS45 on HCC cell invasion, proliferation, and migration was assessed using the Cell Counting Kit-8 (CCK-8), wound healing, and transwell assays. Furthermore, the effect of VPS45 on HCC tumorigenesis in vivo was evaluated through subcutaneous tumor formation assays in BALB/c nude mice. VPS45 is markedly overexpressed in both HCC tissues and cell lines. Its expression escalates with advancing tumor grade and clinical stage, and high VPS45 levels are indicative of poor prognosis. In vitro experiments revealed that VPS45 overexpression significantly boosts HCC cell proliferation, migration, and invasion. Conversely, VPS45 knockdown hindered HCC progression in vivo. Investigation into pathway protein expression suggests that VPS45 facilitates HCC progression through its involvement in the Wnt/β-catenin signaling pathway. The overexpression of VPS45 contributes to the development of malignant phenotypes in HCC cells, resulting in a poor prognosis. Targeting VPS45 may offer a viable therapeutic strategy for managing HCC.

A humanized Caenorhabditis elegans model for studying pathogenic mutations in VPS45, a protein essential for membrane trafficking, associated with severe congenital neutropenia

VPS45, one of the essential membrane trafficking factors, has been identified as a cause of severe congenital neutropenia 5 (SCN5), but its pathophysiological role remains unknown. Here, we developed a humanized C. elegans model for three pathogenic VPS45 variants. We found that wild-type human VPS45 functionally complemented the loss of C. elegans VPS-45 , and the pathogenic human VPS45 variants functioned almost normally with respect to larval development and endocytosis in C. elegans . These results suggest that SCN5-associated mutations have little effect on the core function of VPS45, and/or that the degree of VPS45 requirement varies, depending on the cell/tissue.

PRPS polymerization influences lens fiber organization in zebrafish

BACKGROUND

The self-assembly of metabolic enzymes into filaments or foci highlights an intriguing mechanism for the regulation of metabolic activity. Recently, we identified the conserved polymerization of phosphoribosyl pyrophosphate synthetase (PRPS), which catalyzes the first step in purine nucleotide synthesis, in yeast and cultured mammalian cells. While previous work has revealed that loss of PRPS activity regulates retinal development in zebrafish, the extent to which PRPS filament formation affects tissue development remains unknown.

RESULTS

By generating novel alleles in the zebrafish PRPS paralogs, prps1a and prps1b, we gained new insight into the role of PRPS filaments during eye development. We found that mutations in prps1a alone are sufficient to generate abnormally small eyes along with defects in head size, pigmentation, and swim bladder inflation. Furthermore, a loss-of-function mutation that truncates the Prps1a protein resulted in the failure of PRPS filament assembly. Lastly, in mutants that fail to assemble PRPS filaments, we observed disorganization of the actin network in the lens fibers.

CONCLUSIONS

The truncation of Prps1a blocked PRPS filament formation and resulted in a disorganized lens fiber actin network. Altogether, these findings highlight a potential role for PRPS filaments during lens fiber organization in zebrafish.

Rbm24 controls poly(A) tail length and translation efficiency of crystallin mRNAs in the lens via cytoplasmic polyadenylation

Lens transparency critically requires the abundant accumulation of crystallin proteins, and deregulation of this process causes congenital cataracts in humans. Rbm24 is an RNA-binding protein with highly conserved expression in differentiating lens fiber cells among all vertebrates. We use a zebrafish model to demonstrate that loss of Rbm24 function specifically impedes lens fiber cell differentiation, resulting in cataract formation and blindness. Molecular analyses reveal that Rbm24 interacts with cytoplasmic polyadenylation complex and binds to a large number of lens-expressed messenger RNAs to maintain their stability and protect their poly(A) tail length, thereby crucially contributing to their efficient translation into functional proteins. This work identifies an important mechanism by which Rbm24 posttranscriptionally controls lens gene expression to establish transparency and refraction power.

Lens transparency is established by abundant accumulation of crystallin proteins and loss of organelles in the fiber cells. It requires an efficient translation of lens messenger RNAs (mRNAs) to overcome the progressively reduced transcriptional activity that results from denucleation. Inappropriate regulation of this process impairs lens differentiation and causes cataract formation. However, the regulatory mechanism promoting protein synthesis from lens-expressed mRNAs remains unclear. Here we show that in zebrafish, the RNA-binding protein Rbm24 is critically required for the accumulation of crystallin proteins and terminal differentiation of lens fiber cells. In the developing lens, Rbm24 binds to a wide spectrum of lens-specific mRNAs through the RNA recognition motif and interacts with cytoplasmic polyadenylation element-binding protein (Cpeb1b) and cytoplasmic poly(A)-binding protein (Pabpc1l) through the C-terminal region. Loss of Rbm24 reduces the stability of a subset of lens mRNAs encoding heat shock proteins and shortens the poly(A) tail length of crystallin mRNAs encoding lens structural components, thereby preventing their translation into functional proteins. This severely impairs lens transparency and results in blindness. Consistent with its highly conserved expression in differentiating lens fiber cells, the findings suggest that vertebrate Rbm24 represents a key regulator of cytoplasmic polyadenylation and plays an essential role in the posttranscriptional control of lens development.