Understanding how apoptosis is regulated in salivary gland cells is critical for the development of therapeutics to protect salivary glands from irradiation induced damage and for the treatment of Sjogren's syndrome, salivary tumors and other diseases to which altered apoptosis may contribute. Signal transduction by serine/threonine protein kinases plays an essential role in apoptosis induced by a variety of stimuli. We have previously shown that loss of PKC4 in the parotid gland in vivo provides protection against 3-irradiation induced apoptosis. The long-term goal of my lab is to understand how protein kinase C (PKC) regulates apoptosis and to use this information to develop therapeutic strategies to modulate apoptosis in the salivary gland. We have previously shown the nuclear retention of PKC4 is necessary and sufficient to induce apoptosis, and have identified a C-terminal nuclear localization sequence (NLS) in PKC4 required for nuclear import. We have also recently discovered a polyproline binding site (PxxP) that overlaps with the NLS and that regulates nuclear targeting of PKC4. Nuclear retention of PKC4 in apoptotic cells also requires phosphorylation on key tyrosine residues in the regulatory domain, suggesting that phosphorylation/dephosphorylation of PKC4 functions as a switch to promote cell survival or cell death. We hypothesize that phosphorylation of PKC4 on tyrosine activates its pro-apoptotic function by targeting it to the nucleus, and that nuclear retention of PKC4 is regulated both at the level of both nuclear import and export. Our current studies will focus on identifying the molecular mechanisms that regulate nuclear retention of PKC4 in apoptotic cells, with the goal of identifying rational targets for molecular therapy. In this application we will explore the use of TAT-PKC4 inhibitory peptides to transiently protect the salivary gland from irradiation induced damage in vivo.
Radiation is a key component in the treatment of head and neck cancer, and collateral damage to the salivary glands is often inevitable in these patients due to the proximity of these glands to the radiation site. Each year approximately 40,000 new patients suffer from salivary gland dysfunction as a result of radiation therapy for head and neck cancer, significantly impacting the oral health and quality of life of these individuals. Chronic diminished salivary gland function is thought to result from irreversible cell damage to radiation sensitive cells, particularly the serous acinar cells of the parotid. Recent studies from our lab and others indicate that radiation damage to the salivary glands results in cell death via activation of apoptotic pathways. Our goal is to understand how salivary gland apoptosis is regulated in response to irradiation. These studies may lead to the development of novel therapeutic strategies to protect against salivary gland damage.
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