SEC24C Antibody

What is SEC24C and what is its function in cellular transport?

SEC24C (SEC24 homolog C) is an essential component of the coat protein complex II (COPII) that facilitates vesicle transport from the endoplasmic reticulum (ER) to the Golgi apparatus. SEC24C has two primary functions: physical deformation of the ER membrane into vesicles and selective cargo recruitment for transport to the Golgi complex . The protein has a molecular weight of approximately 118.3 kilodaltons and plays a crucial role in intracellular trafficking pathways . SEC24C works in coordination with other key proteins such as Sar1 and Sec23 to regulate vesicle formation and cargo selection efficiently . Research indicates that SEC24C, together with SEC24D, may have different cargo specificity compared to SEC24A and SEC24B in the COPII complex .

What types of SEC24C antibodies are available for research applications?

SEC24C antibodies are available in various formats optimized for different experimental applications. Current research databases indicate over 110 SEC24C antibody products from 21 suppliers . These antibodies are predominantly available as:

Most antibodies target human SEC24C, with some cross-reacting with mouse and other mammalian orthologs. Applications include Western blotting, immunoprecipitation, immunohistochemistry, immunofluorescence, and ELISA .

How can SEC24C antibodies be applied in studying COPII vesicle formation?

SEC24C antibodies serve as valuable tools for investigating COPII vesicle biogenesis through multiple methodological approaches:

Immunofluorescence microscopy: SEC24C antibodies can be used to visualize ER exit sites (ERES) where COPII vesicles form. Researchers can employ co-localization studies with markers like SEC23-mCherry to identify active sites of vesicle budding . For optimal visualization, a working concentration of approximately 4 μg/ml has been effective in PFA/Triton X-100 fixed and permeabilized cells .

Co-immunoprecipitation assays: SEC24C antibodies can pull down protein complexes to study interactions with other COPII components or cargo receptors. This approach has been particularly useful in identifying SEC24C associations with p24-family members and misfolded proteins like ATZ .

Western blot analysis: For detecting SEC24C in cellular lysates, antibodies at dilutions of approximately 1/250 have demonstrated effectiveness in visualizing the predicted 118 kDa band across multiple human tissue samples including liver, tonsil, and plasma .

When designing experiments to study COPII vesicle formation, researchers should consider combining these approaches with treatments that arrest vesicle trafficking (e.g., brefeldin A and nocodazole) to capture transient COPII intermediates .

What are the optimal protocols for detecting SEC24C phosphorylation during cell cycle progression?

SEC24C undergoes dynamic post-translational modifications (PTMs) throughout the cell cycle, with phosphorylation increasing during mitosis while O-GlcNAcylation decreases. Based on recent research findings, the following protocol elements are crucial for effective detection:

Cell synchronization approach:

• Use thymidine double-block or nocodazole treatment to synchronize cells at specific cell cycle phases

• Confirm synchronization using pH3-Ser10 staining as a mitotic marker

Phosphorylation detection:

• Immunoprecipitate tagged SEC24C (e.g., myc-6xHis-tagged SEC24C from modified cell lines)

• Perform LC-MS/MS analysis to identify specific phosphorylation sites

• Focus on key phosphorylation sites including S888, S937, T941, and T943, with special attention to S888 as a putative CDK1 target in mitosis

Controls and validation:

• Calyculin A treatment serves as a positive control for phosphorylation by inhibiting phosphatases

• Compare phosphorylation patterns between interphase and mitotic cells

• Quantify changes in SEC24C localization as a functional readout of phosphorylation status

Recent research has established that phosphorylation alters SEC24C from discrete puncta at ERES to a diffuse cytosolic distribution, which can be quantified by measuring intensity variance across the cell .

How does SEC24C contribute to the clearance of misfolded proteins through the ERLAD pathway?

SEC24C plays a critical role in endoplasmic reticulum-to-lysosome-associated degradation (ERLAD), a recently characterized pathway for eliminating misfolded proteins. Current research provides the following mechanistic insights:

Role in ATZ clearance:
SEC24C facilitates the trafficking of alpha-1 antitrypsin Z mutant (ATZ), a misfolded protein variant, from the ER directly to lysosomes for degradation. Experimental depletion of SEC24C significantly reduces ATZ colocalization with lysosomal markers (from 51±20% in control cells to 11±11% in SEC24C-depleted cells) .

Interaction with adaptor proteins:
SEC24C forms a complex with p24-family members (particularly TMP21 and TMED9) that function as adaptors linking SEC24C to misfolded cargo. Co-immunoprecipitation experiments have demonstrated that these p24-family proteins interact with both SEC24C and ATZ .

Proposed mechanism:
Current models suggest a multi-step process wherein:

• p24-family proteins recognize misfolded ATZ in the ER

• These adaptors recruit SEC24C to specialized ER exit sites

• The complex facilitates packaging of ATZ into COPII vesicles

• These vesicles bypass the Golgi and are directed to lysosomes via the ERLAD machinery

This pathway represents an important quality control mechanism distinct from both ERAD (ER-associated degradation) and conventional secretory trafficking, highlighting SEC24C's diverse functions in protein homeostasis.

What is the interplay between O-GlcNAcylation and phosphorylation in regulating SEC24C function during cell division?

SEC24C undergoes reciprocal post-translational modifications throughout the cell cycle, with a complex interplay between O-GlcNAcylation and phosphorylation that regulates its localization and function:

Cell cycle-dependent modifications:
Upon mitotic entry, SEC24C transitions from being predominantly O-GlcNAcylated in interphase to heavily phosphorylated in mitosis. This switch correlates with dramatic changes in SEC24C localization and COPII vesicle formation .

Specific modification sites:
Recent mass spectrometry analysis has identified:

• O-GlcNAcylation sites prevalent in interphase

• Phosphorylation sites S888, S937, T941, and T943 increasing during mitosis

• S888 as a putative target for CDK1, the master regulator of mitotic entry

Functional consequences:
The modification state of SEC24C directly impacts its localization:

• O-GlcNAcylated SEC24C in interphase: Concentrated at discrete ER exit sites

• Phosphorylated SEC24C in mitosis: Diffusely distributed throughout the cytoplasm

This redistribution can be quantified by measuring:

• Intensity variance of SEC24C signal (high in interphase, low in mitosis)

• Percentage of cell area occupied by SEC24C puncta

Experimental manipulation using Thiamet G (to increase O-GlcNAcylation) or calyculin A (to increase phosphorylation) demonstrates that these modifications are sufficient to alter SEC24C localization independent of cell cycle phase .

This regulatory mechanism likely represents a fundamental control system for temporarily suspending conventional ER-to-Golgi trafficking during cell division while maintaining cellular integrity.

What are the best practices for optimizing SEC24C antibody use in immunofluorescence studies?

Successful immunofluorescence detection of SEC24C requires careful consideration of several technical parameters:

Fixation and permeabilization:
PFA/Triton X-100 fixation has been validated for SEC24C detection in cellular studies. This method preserves the punctate pattern of SEC24C at ER exit sites while allowing antibody accessibility .

Antibody concentration optimization:
Starting with approximately 4 μg/ml concentration has proven effective for commercially available antibodies, though titration may be necessary depending on the specific antibody and cell type .

Controls and validation strategies:

• Knockdown/knockout validation: Compare staining between control and SEC24C-depleted cells using validated shRNA or CRISPR methods

• Co-localization with known markers: Use SEC23-mCherry as a positive control for ER exit sites

• Functionality tests: Chemical inhibitors like brefeldin A plus nocodazole can trap secretory proteins at ER exit sites, enhancing signal and confirming specificity

Advanced visualization approach:
For studying dynamic changes in SEC24C localization:

• Quantify the variance in SEC24C signal intensity across the cell area

• Measure the percentage of total cell area occupied by SEC24C-positive puncta

• Compare these metrics across different experimental conditions or cell cycle stages

This quantitative approach is particularly valuable when examining how post-translational modifications affect SEC24C distribution between punctate ER exit sites and diffuse cytoplasmic localization.

How can researchers effectively evaluate SEC24C knockdown efficiency in functional studies?

When conducting SEC24C knockdown experiments to assess its functional roles, comprehensive validation is essential:

Western blot validation:

• Use antibodies at approximately 1/250 dilution for detecting the 118 kDa SEC24C band

• Include appropriate loading controls (β-actin or GAPDH)

• Quantify depletion efficiency through densitometry analysis, normalizing to loading controls

Complementary validation approaches:

• qRT-PCR to measure SEC24C mRNA levels

• Immunofluorescence to confirm protein depletion at the single-cell level

• Functional readouts to assess biological consequences of knockdown

Expected functional consequences of efficient knockdown:

• Decreased colocalization of cargo proteins (like ATZ) with lysosomal markers (from ~51% to ~11%)

• Altered distribution of other COPII components

• Accumulation of specific cargo proteins that depend on SEC24C for export

Rescue experiments:
To confirm specificity of knockdown phenotypes, researchers should design rescue experiments using:

• RNAi-resistant SEC24C constructs (containing silent mutations in the target sequence)

• Careful titration of expression levels to match endogenous protein amounts

• Functional assays to demonstrate restoration of SEC24C-dependent processes

When interpreting knockdown results, researchers should consider potential compensatory upregulation of other SEC24 isoforms (particularly SEC24D) that may partially mask phenotypes.

How is SEC24C involved in disease mechanisms and potential therapeutic targets?

Emerging research is uncovering SEC24C's role in various pathological conditions:

Protein misfolding diseases:
SEC24C's function in the ERLAD pathway makes it particularly relevant to conditions characterized by toxic protein aggregation. For alpha-1 antitrypsin deficiency, SEC24C facilitates clearance of the misfolded ATZ variant through direct ER-to-lysosome trafficking. Enhancing this SEC24C-dependent pathway represents a potential therapeutic strategy for reducing proteotoxicity .

Cell cycle dysregulation:
The dynamic post-translational modification of SEC24C during cell division suggests potential roles in pathologies involving aberrant cell cycle control. The identification of SEC24C as a target of CDK1, a master regulator of mitosis, positions it at the intersection of secretory trafficking and cell division control systems .

Future therapeutic directions:

• Small molecule modulators of SEC24C activity or its post-translational modifications

• Gene therapy approaches to enhance SEC24C-dependent clearance pathways

• Targeted manipulation of SEC24C interactions with cargo adaptors like p24-family proteins

As research progresses, a deeper understanding of how SEC24C contributes to cellular proteostasis will likely reveal additional connections to human disease and therapeutic opportunities.

What are the latest techniques for studying SEC24C dynamics in living cells?

Cutting-edge approaches for investigating SEC24C dynamics in live cells include:

CRISPR-based endogenous tagging:
Rather than overexpression systems, researchers have developed CRISPR methods to introduce epitope tags (e.g., myc-6xHis) into the endogenous sec24c locus. This approach maintains native expression levels and promoter control while enabling visualization and biochemical analysis .

Live-cell imaging technologies:

• Fluorescent protein fusions with SEC24C to monitor real-time changes in localization

• Photo-activatable or photo-switchable tags to track specific SEC24C populations

• FRAP (Fluorescence Recovery After Photobleaching) to measure dynamics at ER exit sites

Biosensors for post-translational modifications:
Advanced detection methods for visualizing SEC24C modifications in real-time are being developed, potentially allowing researchers to correlate changes in phosphorylation or O-GlcNAcylation with functional outcomes in living cells.

Correlative light and electron microscopy (CLEM):
This approach combines the molecular specificity of fluorescence imaging with the ultrastructural resolution of electron microscopy, providing unprecedented insights into SEC24C localization relative to COPII vesicle formation.

These technologies promise to reveal the dynamic regulation of SEC24C with temporal and spatial resolution previously unattainable, advancing our understanding of both fundamental cell biology and disease mechanisms.

What are the most significant unanswered questions in SEC24C research?

Despite significant advances in understanding SEC24C function, several critical questions remain unanswered and represent important areas for future investigation:

• Cargo specificity mechanisms: How does SEC24C recognize its specific cargo proteins, and what structural features distinguish its selectivity from other SEC24 isoforms?

• Regulatory networks: What is the complete set of kinases and O-GlcNAc transferases/hydrolases that control SEC24C post-translational modifications throughout the cell cycle?

• Isoform redundancy and specialization: To what extent can other SEC24 family members compensate for SEC24C loss, and which functions are uniquely dependent on SEC24C?

• Tissue-specific roles: Does SEC24C have specialized functions in different tissues or developmental contexts?

• Pathological relevance: How do alterations in SEC24C function contribute to human diseases beyond the currently established connections to protein misfolding disorders?