Recombinant Macaca fascicularis 60S ribosomal protein L24 (RPL24)

What is Recombinant Macaca fascicularis 60S Ribosomal Protein L24 (RPL24)?

RPL24 is a component of the 60S ribosomal subunit derived from Macaca fascicularis (Crab-eating macaque or Cynomolgus monkey). The recombinant form is typically produced in expression systems to generate a full-length protein for research applications. While traditionally associated with the ribosome's large subunit in protein synthesis, recent research has uncovered additional roles in microRNA processing and cellular stress responses. The protein is identified by UniProt accession number P61122 and consists of 157 amino acids with specific structural domains that contribute to its various functions .

What are the recommended storage and handling conditions for Recombinant RPL24?

For optimal stability and activity maintenance, Recombinant Macaca fascicularis RPL24 requires specific storage and handling protocols:

Importantly, repeated freeze-thaw cycles should be avoided as they lead to protein degradation. Prior to reconstitution, it is recommended to briefly centrifuge the vial to bring contents to the bottom. These handling conditions are critical for maintaining protein integrity and experimental reproducibility .

How is Recombinant Macaca fascicularis RPL24 typically expressed and purified?

Recombinant Macaca fascicularis RPL24 is commonly expressed in yeast expression systems, which provide appropriate post-translational modifications and protein folding. The expression typically covers the full protein length (amino acids 1-157). Commercial preparations generally achieve >85% purity as determined by SDS-PAGE analysis. The tag type for purification may vary depending on the manufacturing process but is typically determined during production and specified for each preparation. For experimental use, researchers should reconstitute the protein according to the manufacturer's recommendations, typically in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

What is the subcellular localization of RPL24 and why is it significant?

While RPL24 was traditionally considered a primarily cytoplasmic protein associated with ribosomes, fractionation studies in HEK293T cells have demonstrated that it is present in both nuclear and cytoplasmic compartments. This dual localization is functionally significant because it supports roles beyond protein synthesis. In the nucleus, RPL24 interacts with microRNA processing machinery and directly binds to primary microRNA transcripts (pri-miRs), influencing their maturation. The presence of RPL24 in different cellular compartments suggests it may function as a regulatory link between translation and gene expression regulation pathways .

How does RPL24 influence microRNA processing in mammalian cells?

RPL24 functions as a regulator of microRNA (miRNA) processing in mammalian cells, primarily acting as an inhibitor of pri-miRNA maturation. Research using siRNA-mediated knockdown of RPL24 in HEK293T cells has demonstrated that reducing RPL24 levels leads to increased expression of specific mature miRNAs, with miR-608 showing over 3-fold increase compared to control conditions. This regulatory mechanism appears to involve:

• Direct binding of RPL24 to specific pri-miRNAs in the nucleus

• Interaction with DDX5, a component of the microprocessor complex involved in miRNA processing

• Inhibition of pri-miRNA processing through both direct binding and interaction with processing machinery

Immunoprecipitation experiments with FLAG-tagged RPL24 followed by RNA extraction have shown enrichment of pri-miR-608 and pri-miR-196b in the precipitated fractions, indicating direct interaction. This regulatory function represents a novel role for a ribosomal protein in post-transcriptional gene regulation .

What is the relationship between RPL24 and tRF (tRNA fragment) production?

Knockdown of RPL24 in HEK293T cells induces the production of specific transfer RNA fragments (tRFs), particularly 5'-half tRFs. RNA-seq analysis revealed altered levels of 20 nuclear genome-originated, 31-35 base long tRFs following RPL24 knockdown, with 19 showing increased expression. Of these upregulated tRFs, 17 were 5'-half tRFs, predominantly originating from histidine (7) and glutamine (8) tRNAs.

These 5'-half tRFs are typically produced in the cytoplasm by angiogenin (ANG) in response to cellular stress and contribute to cell survival by promoting stress granule formation and inhibiting apoptosis. Comparative analysis with ANG overexpression datasets revealed that tRFs upregulated after RPL24 knockdown are identical to those induced by ANG overexpression, suggesting that RPL24 depletion triggers ANG-mediated tRF production through cellular stress induction .

Table 1: Characteristics of tRFs induced by RPL24 knockdown

What protein interactions does RPL24 form in nuclear and cytoplasmic compartments?

To understand RPL24's functional mechanisms, researchers have performed immunoprecipitation (IP) of FLAG-tagged RPL24 followed by mass spectrometry (MS) analysis in both nuclear and cytoplasmic fractions. These experiments identified over 100 interacting proteins in each compartment, with approximately half shared between nuclear and cytoplasmic fractions.

Notably, the RNA helicase DDX5, a component of the microprocessor complex involved in miRNA processing, showed 4-fold enrichment in the nuclear fraction (p=0.003). This interaction was independently confirmed by immunoblot analysis. No interaction between RPL24 and angiogenin (ANG) was detected in the cytoplasmic fraction, suggesting that RPL24's effect on ANG-produced tRF halves is indirect, likely through induced cellular stress rather than direct protein-protein interaction .

These findings highlight RPL24's dual functionality and provide mechanistic insight into how a ribosomal protein can influence non-ribosomal processes like miRNA biogenesis.

What experimental approaches are effective for studying RPL24 function?

Multiple complementary experimental approaches have proven effective for investigating RPL24 function:

Table 2: Experimental approaches for studying RPL24 function

These approaches can be combined to develop a comprehensive understanding of RPL24's various functions in different cellular compartments .

How does RPL24 knockdown affect cellular processes beyond translation?

RPL24 knockdown elicits diverse effects on cellular processes beyond its canonical role in translation:

• miRNA Processing: Reduction of RPL24 increases levels of specific miRNAs (notably miR-608 and miR-196b) through relief of inhibition on pri-miRNA processing. Conversely, other miRNAs (e.g., miR-185, miR-126) show decreased expression through indirect mechanisms.

• tRF Production: RPL24 knockdown induces production of 5'-half tRFs derived primarily from histidine and glutamine tRNAs, mediated by ANG activation in response to cellular stress.

• Stress Response: The induction of tRFs suggests activation of cellular stress response pathways, potentially including stress granule formation.

• Indirect Effects on Gene Expression: Changes in miRNA levels would be expected to have downstream effects on numerous target mRNAs, potentially affecting diverse cellular pathways.

These findings highlight RPL24 as a multifunctional protein that interfaces between translation, RNA processing, and stress response pathways, suggesting coordination between these cellular processes .

What is the mechanism by which RPL24 inhibits pri-miR processing?

The mechanism of RPL24-mediated inhibition of pri-miRNA processing involves two primary components:

• Direct Binding to pri-miRNAs: Immunoprecipitation experiments have demonstrated that RPL24 binds directly to specific pri-miRNAs, including pri-miR-608 and pri-miR-196b. This binding may interfere with recognition or processing by the microprocessor complex.

• Interaction with Microprocessor Components: RPL24 interacts with DDX5, a component of the microprocessor complex. This interaction may inhibit the activity of the microprocessor on bound pri-miRNAs.

Importantly, pri-miRNAs corresponding to miRNAs that are downregulated by RPL24 knockdown (miR-185, miR-126) were not enriched in RPL24 immunoprecipitation, suggesting that these effects are indirect and may involve different mechanisms, such as translational repression or interactions with other ribosomal proteins like RPS15 .

How does RPL24 function differ between mammals and plants?

The role of RPL24 in RNA processing appears to be evolutionarily conserved between mammals and plants, though with notable mechanistic differences:

In Arabidopsis, STV1 indirectly influences the transcription of many pri-miRs by altering Pol II occupancy at miRNA promoters, potentially by affecting levels of transcription factors that regulate miRNA transcription. This transcriptional role has not been thoroughly investigated in mammalian systems and represents an area for future research .

What technical considerations are important for RPL24 immunoprecipitation experiments?

When performing RPL24 immunoprecipitation experiments, several technical considerations are critical:

• Protein Tagging: FLAG-tag on the C-terminus of RPL24 has proven effective for immunoprecipitation studies.

• Cellular Fractionation: Separating nuclear and cytoplasmic fractions before immunoprecipitation helps distinguish compartment-specific interactions and prevents masking of nuclear interactors by abundant cytoplasmic partners.

• Buffer Composition: For IP followed by mass spectrometry, washing samples in detergent- and glycerol-free buffer for the final washes improves MS results.

• Controls: Empty vector transfections serve as essential controls for identifying specific interactions.

• Sample Division: After initial washing, dividing samples for different analyses (MS, immunoblotting, RNA extraction) allows comprehensive characterization from a single experiment.

• Antibody Selection: For immunoblotting verification, specific antibodies against RPL24 (Proteintech, 17082-1-AP, 1:1000) and potential interacting partners like DDX5 (Proteintech, 10804-1-AP, 1:700) have been successfully employed.

• Protein Quantification: Bradford or Lowry assays should be used to determine protein concentrations before immunoblotting, with standard loading of approximately 5 μg/sample .

How can researchers validate RPL24's effect on specific miRNAs?

To validate RPL24's effect on specific miRNAs, researchers can employ several complementary approaches:

• siRNA-mediated Knockdown: Transfect cells with 50 nM siPOOLs targeting RPL24 (or non-targeting controls) using appropriate transfection reagents like HiPerFect, then measure changes in miRNA levels by RT-qPCR or small RNA sequencing 48-72 hours post-transfection.

• Direct Binding Assessment: Perform immunoprecipitation of FLAG-tagged RPL24 followed by RNA extraction and qPCR for specific pri-miRNAs to determine direct interactions. Compare enrichment of pri-miRNAs corresponding to miRNAs affected by RPL24 knockdown.

• Subcellular Localization Confirmation: Use cellular fractionation followed by immunoblotting with antibodies against RPL24 and appropriate compartment markers (e.g., Histone H3 for nucleus, α-Tubulin for cytoplasm) to confirm RPL24's presence in both compartments.

• Protein Interaction Verification: Immunoprecipitate FLAG-tagged RPL24 and perform immunoblotting for microprocessor components like DDX5 to confirm interactions with the miRNA processing machinery.

• Size-specific Analysis: For validating effects on small RNAs like miRNAs and tRFs, separate RNAs by PAGE and excise size-specific bands (e.g., ≤50-nt for tRFs) before proceeding with RT-qPCR to prevent interference from full-length precursors .

What role might RPL24 play in cellular stress responses?

RPL24 appears to be connected to cellular stress responses through several mechanisms:

• tRF Production Regulation: RPL24 knockdown leads to increased production of 5'-half tRFs, which are typically generated by angiogenin (ANG) in response to cellular stress. These tRFs promote stress granule formation and inhibit apoptosis, suggesting a role in stress adaptation.

• Translation-Stress Interface: As a ribosomal protein, changes in RPL24 levels or activity would affect translation, potentially serving as a mechanism to coordinate protein synthesis with stress responses.

• miRNA-mediated Regulation: The changes in miRNA expression following RPL24 depletion may contribute to stress response pathways by altering the expression of stress-related genes.

• Indirect ANG Activation: While RPL24 does not directly interact with ANG, its depletion appears to induce ANG activity, suggesting that RPL24 status may serve as a sensor or signal for certain types of cellular stress.

• Connection to Other Ribosomal Proteins: RPL24 interacts with other ribosomal proteins like RPS15, which has also been implicated in miRNA regulation, suggesting potential coordinated roles in integrating translation and stress responses .