BCCIP Human
Description
Molecular Structure and Isoforms
Human BCCIP exists in two major isoforms due to alternative RNA splicing:
-
BCCIPα (322 residues)
-
BCCIPβ (314 residues)
Both isoforms share identical N-terminal residues (1–258) but diverge in their C-terminal regions . Structural studies reveal:
Genomic Stability
Cell Cycle Regulation
-
Modulates CDK2 activity via p21 interaction, delaying G1/S transition .
-
Required for spindle integrity; knockdown causes mitotic defects (disorganized spindles, chromosome missegregation) .
Ribosome Biogenesis
Clinical Significance in Cancer
BCCIP exhibits dual roles in tumorigenesis:
Tumor Suppression
-
Downregulation observed in 56–89% of ovarian, renal, and colorectal cancers .
-
Conditional knockout mice develop medulloblastoma and hepatocellular carcinoma .
Tumor Progression Dependency
-
Paradoxically, restored BCCIP expression supports advanced tumor growth .
-
Acts as a Suppressor of Initiation but Requisite for Progression (SIRP):
Cancer-Associated BCCIP Expression
| Cancer Type | Downregulation Frequency | Clinical Correlation |
|---|---|---|
| Ovarian Cancer | 74% | Advanced stage, poor prognosis |
| Renal Cell Carcinoma | 89% | Metastasis, high grade |
| Colorectal Cancer | 75% | Lymph node invasion |
Experimental Models and Research Findings
Embryonic Development
-
BCCIP knockout causes embryonic lethality in mice (E7.5–E9.5) due to proliferation defects .
-
Rescue experiments show p53 deletion mitigates neurogenesis defects in BCCIP-deficient mice .
Recombinant Protein Applications
-
Human recombinant BCCIPβ (38.6 kDa, His-tagged) is used to study BRCA2/p21 interactions .
-
Key applications:
Therapeutic Implications
Product Specs
Q&A
What is BCCIP and what are its primary functions in human cells?
BCCIP is a nuclear protein identified based on its interactions with tumor suppressors BRCA2 and p21 . It plays critical roles in homologous recombination (HR) repair of DNA double-strand breaks (DSBs), cell cycle progression, chromosome stability, and biogenesis of ribosome 60S subunits . BCCIP helps maintain genome stability by resolving spontaneous DNA damage and is essential for embryonic development, as knockdown or knockout in mice causes embryonic lethality .
What are the known isoforms of human BCCIP and how do they differ?
In humans, there are two isoforms resulting from alternative RNA splicing:
-
BCCIPα (322 residues)
-
BCCIPβ (314 residues)
Both isoforms share identical N-terminal 258 residues but differ in their C-terminal regions . They are also known as TOK-1α and TOK-1β respectively . BCCIPβ is evolutionarily conserved across eukaryotes from yeast to mammals, while BCCIPα only exists in humans, suggesting human-specific functions .
What is the genomic structure of human BCCIP?
The human BCCIP gene contains nine exons, with alternative splicing of the 3'-terminal exons producing the two isoforms . The gene has a complex genomic organization:
-
It lies head-to-head and shares a bi-directional promoter with the uroporphyrinogen III synthase (UROS) gene
-
The last three exons of BCCIP overlap with a DEAD/H helicase-like gene (DDX32)
-
Both neighboring genes are transcribed in the opposite orientation of BCCIP
What is known about the three-dimensional structure of human BCCIP?
Crystal structures of an N-terminal truncated human BCCIPβ (residues 61-314) have been determined at resolutions of 3.06Å and 2.20Å . Key structural features include:
| Crystal Form | Resolution | Key Features |
|---|---|---|
| Native1 | 3.06 Å | Highly anisotropic diffraction, open conformation of L67 flap |
| Native2 | 2.20 Å | Closed conformation of L67 flap (aa269-287) |
Structurally, BCCIP resembles GCN5-related acetyltransferases (GNATs) with an rmsd of 2.0 Å over 80 pairs of Cα atoms, despite having different sequence motifs .
How does BCCIP's structure inform its potential molecular functions?
BCCIP's structure reveals several functional implications:
These features suggest BCCIP may have enzymatic activity and contains specific binding sites for partner proteins like BRCA2 and p21 .
What are optimal methods for detecting BCCIP expression in human tissues?
A multi-modal approach is recommended:
-
mRNA detection:
-
RT-qPCR with isoform-specific primers targeting the unique C-terminal regions
-
RNA-seq with proper splice junction analysis to distinguish isoforms
-
-
Protein detection:
-
Western blotting with antibodies against:
-
Common N-terminal region (detects both isoforms)
-
Isoform-specific C-terminal regions
-
-
Immunohistochemistry for spatial localization in tissues
-
When analyzing expression, researchers should consider examining both isoforms separately as they may have distinct functions .
What purification strategies yield high-quality BCCIP protein for structural and biochemical studies?
The disordered N-terminal region (residues 1-60) should be considered for removal to improve protein behavior while maintaining key functional domains .
How does BCCIP regulate homologous recombination at the molecular level?
BCCIP regulates HR through multiple mechanisms:
-
It facilitates BRCA2 and RAD51 nuclear focus formation at DNA damage sites, essential for HR initiation
-
Multiple domains appear important for HR regulation:
-
BCCIP specifically regulates HR but not non-homologous end joining (NHEJ):
-
BCCIP deficiency leads to increased levels of spontaneous single-stranded DNA and DSBs, indicating its importance in resolving endogenous DNA damage .
What experimental designs best reveal BCCIP's role in DNA repair?
| Experimental Approach | Purpose | Key Controls/Considerations |
|---|---|---|
| HR Reporter Assays | Measure homology-directed repair efficiency | Compare BCCIP-depleted vs. control cells |
| RAD51/BRCA2 Focus Formation | Assess HR pathway functionality | Time-course after DNA damage induction |
| Comet Assay | Quantify DNA strand breaks | Include positive controls (e.g., H₂O₂ treatment) |
| Chromosome Spread Analysis | Examine structural abnormalities | Blind scoring to prevent bias |
| Sister Chromatid Exchange | Measure recombination frequency | Cell cycle synchronization |
| γ-H2AX Foci Formation | Quantify DNA damage response | Co-staining with cell cycle markers |
When designing these experiments, researchers should consider cell cycle effects, as BCCIP functions may be phase-dependent due to its interaction with cell cycle regulators like p21 .
What is known about BCCIP expression patterns in human cancers?
BCCIP expression varies across cancer types with potential prognostic implications:
The reduced expression of BCCIP in kidney tumors suggests a tumor suppressor role . This is supported by animal models where BCCIP heterozygous and mosaic knockout mice spontaneously develop hepatocellular carcinoma and B-cell lymphoma .
How does BCCIP deficiency affect embryonic development?
BCCIP deficiency has profound developmental effects:
-
Either knockdown or complete knockout of BCCIP in mice leads to embryonic lethality
-
The lethality is attributed to:
-
BCCIP-deficient mouse embryo fibroblast cells exhibit:
These findings highlight BCCIP's essential role in maintaining genomic stability during development.
What is the significance of BCCIP in ribosome biogenesis and how does this connect to its DNA repair functions?
BCCIP plays a crucial yet distinct role in 60S ribosomal subunit biogenesis:
| Process | BCCIP Function | Potential Connection to DNA Repair |
|---|---|---|
| 60S Ribosome Biogenesis | Essential factor for production | Coordination of growth with genome stability |
| eIF6 Recruitment | Facilitator of nucleolar localization | Sensing of translational status |
| pre-rRNA Processing | Regulator of 12S pre-rRNA levels | Nucleolar stress response activation |
This dual role in ribosome biogenesis and DNA repair suggests BCCIP may function as a molecular link coordinating protein synthesis capacity with genome maintenance . This connection represents an emerging area for investigation, with potential implications for understanding how cells balance growth with genome protection.
What emerging technologies could advance our understanding of BCCIP function?
| Technology | Application to BCCIP Research | Advantage |
|---|---|---|
| Cryo-EM | Higher resolution structures of full-length BCCIP with binding partners | Captures dynamic complexes |
| Proximity Labeling (BioID/TurboID) | Identifying the complete BCCIP interactome | Detects weak/transient interactions |
| CRISPR Base Editing | Introduction of specific BCCIP mutations | Avoids embryonic lethality of complete knockout |
| Live-Cell Single-Molecule Imaging | Visualizing BCCIP dynamics during DNA repair | Real-time activity assessment |
| Crosslinking Mass Spectrometry | Mapping precise interaction interfaces | Detailed structural insights |
These approaches could help resolve outstanding questions about BCCIP's enzymatic activity, isoform-specific functions, and its exact mechanisms in coordinating DNA repair with other cellular processes .
What are the major unresolved questions about BCCIP in human biology?
Several critical aspects of BCCIP remain to be fully elucidated:
-
The enzymatic activity suggested by BCCIP's structural similarity to acetyltransferases needs verification and characterization
-
The human-specific BCCIPα isoform's unique functions compared to the evolutionarily conserved BCCIPβ require investigation
-
The precise molecular mechanisms by which BCCIP regulates both DNA repair and ribosome biogenesis need clarification
-
The regulation of BCCIP expression and activity through post-translational modifications remains poorly understood
-
The therapeutic potential of targeting BCCIP in cancer treatment strategies warrants exploration, particularly given its reduced expression in some tumor types
Product Science Overview
BCCIP is known to associate with BRCA2 and RAD51 during HR-mediated DNA repair. It is recruited to stalled replication forks and prevents the degradation of nascent DNA strands by the MRE11 nuclease . This function is essential for protecting the integrity of the genome, especially under conditions of replication stress, which can lead to genomic instability and oncogenic transformation if not properly managed .
Replication stress occurs when the progression of replication forks is hampered, leading to the formation of DNA lesions such as double-strand breaks (DSBs). BCCIP plays a pivotal role in stabilizing these stalled replication forks and preventing their collapse. In the absence of BCCIP, there is an increase in replication fork stalling and subsequent DNA double-strand break formation . This highlights the importance of BCCIP in maintaining the stability of the genome during DNA replication.
Studies using mouse models have demonstrated the essential roles of BCCIP in embryonic development and chromosome stability. Conditional knockdown of BCCIP in mice leads to impaired cellular proliferation and increased apoptosis, resulting in embryonic lethality before day E11.5 . BCCIP-deficient mouse embryonic fibroblasts (MEFs) exhibit significant chromosomal structural alterations, including increased chromatid breaks and sister chromatid union (SCU), which can impair chromosome segregation during mitosis .
Given its critical role in DNA repair and genomic stability, BCCIP is a protein of interest in cancer research. Deficiencies in BCCIP function can lead to increased genomic instability, a hallmark of cancer development. Understanding the mechanisms by which BCCIP operates can provide insights into potential therapeutic targets for cancer treatment.
