### STK4 Gene Overview

**Gene Symbol**: STK4  
**Alternative Names**: MST1  
**Location**: Chromosome 3, 3p21.1  

STK4 encodes a serine/threonine kinase that plays a crucial role in the regulation of apoptosis and the Hippo signaling pathway, which is important for tumor suppression and controlling organ size.

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### 1. Associated Genes
Besides the interactions described in the summaries, STK4 has associations with the following genes:
- **STK3 (MST2)**: Phylogenetically related kinase functioning in the same signaling cascade.
- **LATS1/2**: Kinases downstream in the Hippo pathway, which STK4 activates.
- **YAP1/TAZ (WWTR1)**: Oncoproteins whose activity is inhibited by the Hippo pathway, involving STK4.
- **FOXO family members** (FOXO1, FOXO3): Transcription factors involved in apoptosis and oxidative stress response.
- **RASSF1**: Tumor suppressor that can also be part of the Hippo signaling pathway.
- **TNNI3**: Cardiac Troponin I, involved in cardiac muscle contraction, which can be differentially phosphorylated by STK4.

### 2. Aging and Age-Related Diseases
Research suggests that STK4 may play a role in various age-related phenomena and diseases:
- **Aging**: The Hippo signaling pathway, where STK4 is central, influences organ size and metabolic homeostasis, affecting longevity.
- **Cancer**: Due to its pro-apoptotic functions and role in tumor suppression, dysregulation of STK4 has been associated with various cancers, especially as tumor development is often linked to aging.
- **Cardiovascular Diseases**: STK4's involvement in cardiac myocyte differentiation and function can have implications for age-related heart diseases.

### 3. Drug and Drug Classes Interacting with STK4
No drugs are specifically annotated to target STK4 directly. However, the following drug classes interact indirectly through pathways involved with STK4:
- **Proteasome Inhibitors**: Affecting the degradation of proteins in pathways involving STK4 could have effects on apoptosis.
- **Histone Deacetylase Inhibitors (HDACi)**: Depending on their effects on apoptosis, these may affect STK4 function or expression as it phosphorylates histones during apoptosis.
- **Caspase Inhibitors**: As STK4 is cleaved by caspases, inhibiting these could influence STK4 activity in apoptotic contexts.

### 4. Pathways and Biological Processes
STK4 is involved in several key pathways and biological processes:
- **Hippo Signaling Pathway**: Central to regulating cell growth, proliferation, and apoptosis.
- **Apoptosis**: Functions as a pro-apoptotic kinase, activating pathways that lead to programmed cell death.
- **Cell Cycle Regulation**: Influences the proliferation of various cell types, including hepatocytes.
- **DNA Damage Response**: Participates in the cellular response to DNA damage, facilitating apoptosis through p53-dependent mechanisms.
- **Transcription Regulation**: Phosphorylates transcription factors (e.g., FOXO1, FOXO3) that regulate genes important for stress responses, metabolism, and apoptosis.
- **Signal Transduction in Cardiac Function**: Involved in modifications of cardiac proteins that affect muscle contraction.

In summary, STK4 is a multifunctional kinase that plays pivotal roles in apoptotic signaling and the regulation of cell proliferation through the Hippo signaling pathway. It is associated with aging and age-related diseases, has a number of interactive proteins, and influences crucial cellular pathways.