PSIP1 Human
Description
Transcriptional Regulation
PSIP1 acts as a transcriptional coactivator by bridging chromatin-modifying enzymes (e.g., MLL1) to target genes, including HOX clusters . It also regulates alternative splicing by recruiting splicing factors to H3K36me3-marked regions .
Genome Stability
PSIP1 suppresses R-loops (RNA-DNA hybrids) at transcription sites, preventing DNA damage. Depletion of PSIP1 increases R-loop accumulation, γ-H2AX (DNA damage marker), and replication stress .
Mitochondrial Respiration
In T-cell acute lymphoblastic leukemia (T-ALL), PSIP1 knockdown reduces COX20 (a mitochondrial complex assembly factor), impairing respiration and cell proliferation .
Dual Role in T-ALL
PSIP1 exhibits tumor-suppressive and dependency factor roles:
-
Tumor Suppression: Loss of Psip1 accelerates T-ALL initiation in mice by reducing H3K27me3 signaling .
-
Dependency Factor: PSIP1 depletion in established T-ALL cell lines reduces proliferation and mitochondrial respiration .
HIV Integration
PSIP1/p75 is a critical host factor for HIV-1 integration. Small-molecule inhibitors targeting the PSIP1-integrase interaction are under investigation for antiviral therapies .
Cancer Tissue Expression
High PSIP1 expression is observed in multiple cancers, including prostate, lung, and breast, though its prognostic significance remains unclear .
Environmental and Chemical Interactions
PSIP1 expression is modulated by environmental toxins and chemicals:
Knockout Models
TALEN-mediated knockout of PSIP1 in human cells confirms its necessity for HIV integration and highlights its dispensability in normal hematopoiesis .
shRNA Depletion
Short-hairpin RNA (shRNA) targeting PSIP1 in human/mouse cell lines demonstrates:
Therapeutic Implications
PSIP1’s dual role in cancer and its role in HIV integration make it a candidate for targeted therapies. Inhibitors of PSIP1-integrase interaction could block HIV replication, while PSIP1-targeted strategies may disrupt T-ALL maintenance .
Product Specs
Q&A
What are the primary functional domains of PSIP1, and how do they influence experimental design?
PSIP1 encodes two isoforms: p75 (LEDGF/p75) and p52. The p75 isoform contains an integrase-binding domain (IBD) critical for HIV-1 integration and a PWWP domain that binds H3K36me2/3-modified chromatin. The p52 isoform lacks the IBD but retains chromatin-binding capabilities .
Methodological considerations:
-
Domain-specific knockouts: Use TALENs or CRISPR-Cas9 to delete exons encoding the IBD (exons 11–15) while preserving the PWWP domain .
-
Isoform discrimination: Employ antibodies targeting unique C-terminal regions (e.g., A300-847 for p52) .
Key findings:
-
Whole-gene PSIP1 knockout in Jurkat T cells reduces HIV-1 integration efficiency by 95% .
-
p52 retains splicing regulation activity via H3K36me3 binding despite lacking the IBD .
How does PSIP1 facilitate HIV-1 integration, and what models validate this mechanism?
PSIP1/p75 tethers HIV-1 integrase to transcriptionally active genomic regions enriched in H3K36me3.
Experimental validation:
-
Integration site analysis: Perform deep sequencing of HIV-1 proviral DNA in PSIP1−/− vs. wild-type cells .
-
Chromatin immunoprecipitation (ChIP): Map PSIP1 occupancy relative to H3K36me3 using antibodies validated in knockout controls .
Data contradictions:
Early RNAi studies reported residual integration activity (15–30% of control), whereas TALEN-mediated PSIP1−/− cells show <5% activity, highlighting the importance of complete gene deletion over partial knockdown .
What baseline phenotypic data exist for PSIP1 knockout models?
PSIP1−/− mice exhibit perinatal lethality (60%), skeletal homeotic transformations, and reduced mitochondrial respiration in T-cell leukemias .
Standard phenotyping workflow:
How can PSIP1 function as both a tumor suppressor and oncogenic dependency factor in T-ALL?
Paradox resolution strategies:
-
Temporal genetic ablation: Use inducible Cre systems to delete PSIP1 during leukemia initiation vs. maintenance phases.
-
Epigenetic profiling: Compare H3K27me3 occupancy in PSIP1−/− premalignant thymocytes vs. established leukemias .
Key mechanistic insights:
-
Tumor suppression: PSIP1 loss during initiation reduces H3K27me3 at polycomb-repressed loci, accelerating leukemogenesis.
-
Oncogenic dependency: Established T-ALL requires PSIP1/p75 to maintain COX20 expression and oxidative phosphorylation .
What advanced techniques resolve PSIP1’s dual roles in chromatin binding and splicing?
Integrated multi-omics approach:
-
ChIP-exo: Map PSIP1-p52 binding at near-base-pair resolution across splice sites .
-
Single-molecule RNA FISH: Quantify alternative splicing efficiency (e.g., Vcan exon 8 skipping) in live PSIP1−/− cells .
Critical controls:
-
H3K36me3 mutagenesis: Replace endogenous histone H3 with H3K36A mutants via CRISPR-HDR.
-
Splicing factor co-IP: Validate PSIP1-SRSF1 interactions using crosslinking IP in splicing-active nuclear fractions .
How do ALLINI-class inhibitors affect HIV-1 latency in PSIP1-edited cells?
Contradictory evidence:
While ALLINIs block HIV-1 particle maturation independently of PSIP1, PSIP1−/− cells show altered proviral transcriptional activity .
Resolution methodology:
-
Dual-reporter HIV constructs: Incorporate LTR-driven GFP and viral particle-associated mCherry to decouple integration from late-stage effects.
-
PRO-Seq: Measure RNA polymerase II engagement at integration sites in ALLINI-treated PSIP1−/− cells.
Key data:
| Condition | Integration Efficiency | Transcriptional Burst Frequency |
|---|---|---|
| PSIP1+/+ + ALLINI | 18% of control | 2.3 bursts/hour |
| PSIP1−/− + ALLINI | 4% of control | 0.7 bursts/hour |
Product Science Overview
The PSIP1 gene is located on chromosome 9 and encodes multiple isoforms through alternative splicing. The two main isoforms are p75 and p52, which have distinct functions but share a common N-terminal region. The p75 isoform is a transcriptional coactivator involved in neuroepithelial stem cell differentiation and neurogenesis, while the p52 isoform acts as an adapter to coordinate pre-mRNA splicing .
PSIP1/LEDGF plays a crucial role in various biological processes:
- Transcriptional Regulation: PSIP1 acts as a transcriptional coactivator, enhancing the transcription of specific genes by RNA polymerase II. It binds to DNA and interacts with other transcription factors to regulate gene expression .
- Stress Response: PSIP1 is involved in cellular stress responses, particularly in protecting cells from stress-induced apoptosis. It helps maintain cell viability under stressful conditions .
- Cell Differentiation: PSIP1 is essential for the differentiation of lens epithelial cells into fiber cells, a critical process in lens development. It also plays a role in neurogenesis and the differentiation of neuroepithelial stem cells .
PSIP1 has been implicated in several diseases and conditions:
- Cancer: Overexpression of PSIP1 is associated with various cancers, including lacrimal duct cancer and lymphangiosarcoma. It may promote tumor cell growth and survival .
- HIV Integration: PSIP1 serves as a cellular cofactor for lentiviral integration, including HIV. It facilitates the integration of viral DNA into the host genome, making it a potential target for antiviral therapies .
Recombinant human PSIP1 is produced using E. coli expression systems. The recombinant protein is purified and used in various research applications, including studies on transcriptional regulation, stress response, and cell differentiation. It is available in different forms, such as liquid or lyophilized powder, and is often tagged with His-SUMO for easy purification .
