### HDAC1 Gene Overview

**Gene Symbol**: HDAC1  
**Location**: Human Chromosome 1p36.11  
**Function**: Histone deacetylase; involved in chromatin remodeling, gene expression regulation, and various cellular processes.

### Additional Gene Associations
In addition to the genes mentioned in the summaries (e.g., p53, NR1D2, RELA, SP1, SP3, TSHZ3), HDAC1 has been associated with the following genes:
- **RB1**: Retinoblastoma tumor-suppressor gene; forms complexes with HDAC1.
- **CREBBP**: A transcriptional coactivator that is released upon HDAC1 stimulation.
- **BRAF**: Mutations in BRAF and HDAC1 interactions can influence cancer progression.
- **KAT5 (TIP60)**: Kinase involved in DNA repair that interacts with HDAC1 for transcriptional regulation.

### Aging and Age-Related Diseases
- **Aging**: HDAC1 expression and activity have been linked to age-related changes in gene expression and chromatin structure, which can contribute to cellular senescence. Increased HDAC1 levels may lead to the repression of genes involved in cell cycle regulation.
- **Neurodegeneration**: Research indicates that alterations in HDAC1 function could be implicated in neurodegenerative diseases, such as Alzheimer's disease, where histone modifications play a key role in the pathophysiology.
- **Cancer**: HDAC1 has a well-established role in oncogenesis, particularly in relation to tumor suppressor gene silencing (e.g., p53) and cell cycle regulation, both of which are critical in aging and age-related cancer progression.

### Drug Interactions
**Known Drug Classes**:
- **HDAC Inhibitors**: These include drugs such as:
  - **Vorinostat (SAHA)**: Used in the treatment of cutaneous T-cell lymphoma.
  - **Romidepsin**: Approved for the treatment of peripheral T-cell lymphoma.
  - **Panobinostat**: Used for myeloma therapy.
  - **Entinostat**: Investigated in various solid tumors.

**Other Drugs**:
- **Valproic Acid**: An anticonvulsant that also acts as an HDAC inhibitor, playing a role in epilepsy and bipolar disorder treatment.
- **Scriptaid**: A small-molecule inhibitor that selectively affects HDAC activity.

### Pathways and Biological Processes
HDAC1 is involved in numerous biological pathways, including:
- **Gene Expression Regulation**: Directly affects the transcriptional state by modifying chromatin structure.
- **Cell Cycle Regulation**: Participates in processes that control cell proliferation and apoptosis.
- **Development**: Involved in embryonic development and differentiation through regulation of developmental genes.
- **Neuronal Function**: Modulates neuronal gene expression and synaptic function, impacting learning and memory.
- **Immune Response**: Plays a role in inflammatory response and cell differentiation in immune cells.
- **Circadian Rhythms**: Regulates transcriptional repression of circadian genes, maintaining circadian homeostasis.

In summary, HDAC1 is a multifaceted protein critically involved in gene regulation, chromatin dynamics, and various biological processes that relate to aging and disease. Its modulation by small molecules indicates potential therapeutic avenues for age-related conditions and various cancers.