Browsing Pathways

Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein that functions as a coregulator of several transcription factors and nuclear receptors. Notably, the PELP1 protein has a histone-binding domain, recognizes histone modifications and interacts with several chromatin-modifying complexes. PELP1 serves as a substrate of multitude of kinases, and phosphorylation regulates its functions in various complexes. Further, PELP1 plays essential roles in several pathways including hormonal signaling, cell cycle progression, ribosomal biogenesis, and the DNA damage response. PELP1 expression is upregulated in several cancers, its deregulation contributes to therapy resistance, and it is a prognostic biomarker for breast cancer survival. Recent evidence suggests that PELP1 represents a novel therapeutic target for many hormonal cancers.

Pancreatic delta cells produce somatostatin which functions to inhibit glucagon, insulin, and itself. Somatostatin is stored in granules in the delta cell and is released in response to an increase in blood sugar, calcium, and blood amino acids during absorption of a meal. In the process of somatostatin secretion, glucose must first undergo glycolysis in the mitochondrion to increase ATP in the cell. The inside of the alpha cell then becomes electrically positive due to the closure of potassium channels that were inhibited by ATP. From this closure, the potassium is no longer being shuttled out of the cell, thus depolarizing the cell due to the extra intracellular potassium. The resulting action potential from the increased membrane potential causes the voltage gate calcium channels to open, creating an influx of calcium into the cell. This triggers the exocytosis of somatostatin granules from the delta cell.

Beta cells are found in pancreatic islet cells and their main function is to release insulin. Insulin counteracts glucagon and functions to maintain glucose homeostasis when glucose levels are high. Insulin is contained in granules in the cell as a reserve ready to be released, which is dependent on extracellular glucose levels, and intracellular calcium levels and/or various proteins that activate the vesicle-associated membrane protein on the insulin granules' membranes. In the process of insulin secretion, glucose must first undergo glycolysis to increase ATP in the cell. The inside of the beta cell then becomes electrically positive due to the closure of potassium channels that were inhibited by ATP. From this closure, the potassium is no longer being shuttled out of the cell, thus depolarizing the cell due to the extra intracellular potassium. The resulting action potential from the increased membrane potential causes the voltage gate calcium channels to open, creating an influx of calcium into the cell. This triggers the vesicle-associated membrane protein on the outside of the insulin granule to tether, dock, and fuse with the beta cell membrane. Insulin is then exocytosed from the cell. However, the vesicle-associated membrane protein can be activated by other means in addition to calcium. Acetylcholine can bind to muscarinic acetylcholine receptors on the cell membrane and trigger a G protein cascade. This eventually leads to the activation of inositol trisphosphate to cause calcium release from the rough endoplasmic reticulum so that it can activate the calcium/calmodulin-dependent protein kinase to trigger the vesicle-associated membrane protein. The G protein cascade can also lead to the activation of diacylglycerol and subsequently protein kinase C to lead to the same outcome. Glucagon-like peptide can also trigger a similar G protein cascade when it binds to glucagon-like peptide receptors on the cell membrane of the beta cell. This process involves cAMP and a few other proteins in order to lead to the same eventual outcome of triggering the vesicle-associated membrane protein and the exocytosis of insulin from the beta cell.

Alpha cells are a type of islet cell found in the pancreas that release glucagon. Glucagon counteracts insulin and functions to maintain glucose homeostasis when detected glucose levels are low. Glucagon is contained in granules in the cell as a reserve ready to be released. Extracellular glucose levels and ion channels regulate the secretion of glucagon. Glucose undergoes glycolysis to increase ATP in the cell. The moderate activity of potassium ATP channels causes the membrane potential to be around -70mV. The alpha cell then becomes electrically active due to the closure of potassium channels. The cell membrane becomes depolarized due to voltage dependent sodium, potassium and calcium channels. This causes an increase in action potentials and opens voltage gate calcium channels causing an increase of calcium into the cell. This triggers the exocytosis of glucagon from the cell. Conversely, an increase in extracellular glucose leads to an increase in ATP production and inhibition of potassium ATP channels. The membrane depolarizes to a membrane potential that inactivates voltage dependent calcium channels. This results in decreased intracellular calcium and inhibits exocytosis of glucagon.

The pancreas is crucial in many organisms for properly converting food into usable fuel to be used by cells. It acts as part of the digestive system for a majority of its function as it is connected to the stomach and provides digestive enzymes to the partly digested food brought in by the stomach. The pancreas also serves as an endocrine component, by creating hormones to regulate blood sugar. Insulin, a hormone created by the pancreas (beta cells), acts to lower blood sugar, which is very important as it allows cells in the body to use sugar without inducing hyperglycaemia.