The notch protein is part of the greater picture, the notch signaling pathway. The actual protein serves as a trigger straddling the inside and outside of the cell membrane. When certain proteins bind to the exterior of the notch, the interior releases other proteins which make their way to the cell nucleus to alter gene expression. Some responsibilities delegated to the notch include but are not limited to cell proliferation, cell differentiation, and apoptosis.
Notch proteins are not an universal brand of amino acids, rather they are only found in Metazoans, or animals. Within these creatures, the variety of notch proteins range from notch-1 to notch-4. These notches correspond with five ligands termed Jagged 1, Jagged 2, Delta -1, Delta -2, Delta -3. When cancer or other diseases strike, the notch complex is usually deactivated, leading to a weak T-Cell response.
Typically, Notch is triggered primarily though direct contact, meaning that the external proteins must physically bind them to the exterior. Moreover, each individual cell that makes contact with the notch alters a different gene expression, so the process is very localized and specialized. For example, a particular cell would have to bind to the notch for a signal to activate apoptosis.
What is GSI?
GSI is a man-made pharmacological agent known to block notch activation. It works by inhibiting γ-secretase, an enzyme that cuts off the ends of proteins. Some viruses, like as HIV, must cleave proteins to function properly. With GSI, the HIV retrovirus is effectively prevented from reproducing, thereby halting the progression of the disease.
How GSI Inhibits KS
GSI inhibits the γ-secretase enzyme, which in turn prevents notch signals from reaching KS. Without notch signalling, stem cell growth is stunted and KS is forced to go through apoptosis, or programmed cellular death.
GSI Effects within the in vitro portion of the Experiment
Endothelial cells, or precursors to KS cells, and SLK cells derived from the KS cell line were both treated with GSI for a period between 24-48 hours. After the treatment, the cells were examined for growth arrest and apoptosis. Results showed that the normal endothelial cells were resistant to GSI. Only about 12% ended up going through apoptosis. In comparison, 36% of the treated SLK cells underwent apotosis. More impressively, 51% of the endothelial cells experienced growth after the 48 hour treatment, and 98% went through apoptosis after being treated with a second dose of GSI. Fast-growing endothelial cells were not as resistant to the GSI-- 27% of proliferating cells went through apoptosis after their first dose of GSI. This leads us to believe that faster growing endothelial cells are generally more resistant to GSI treatments if they grow at a slower rate.
Another γ-secreates enzyme Inhibitor
Within the experimentation Lγ -411,575 was also show to block γ-secreates. Results showed that growth arrest occurred in about 44% of the...