DNA damage response and repair in cancer treatment toxicity:

A formidable challenge in the treatment of primary and metastatic brain cancers, especially in children, is the long-term neurocognitive deficiencies resulting from cranial irradiation (IR)-induced hippocampal neuronal apoptosis. Our laboratory has discovered a novel functional connection between the metabolic kinase GSK3β and the Non-homologous End-joining (NHEJ) pathway that repair DNA double-strand breaks (DSBs).  Furthermore, our preliminary data revealed that the NHEJ mediator 53BP1 is directly phosphorylated by GSK3β; meanwhile, increased expression of the classic GSK3β substrate β-catenin is associated with enhanced repair of IR-induced DSBs and survival in hippocampal neurons. Thus, we hypothesize that GSK3 regulates NHEJ-mediated repair of DSBs and determines neuron cytotoxicity following IR via suppression of 53BP1 and β-catenin function. In addition, tumor cells which contain abnormal GSK3β activity will not exhibit GSK3β-mediated protection from IR-induced cytotoxicity. A series of in vitro and in vivo experiments are proposed to test our hypotheses: Aim 1 will identify the GSK3β phosphorylation sites in 53BP1 and determine whether GSK3β-specific phosphorylation direct 53BP1 function in NHEJ and in survival of irradiated hippocampal neurons.  Aim 2 will determine whether GSK3β regulates 53BP1 through suppressing β-catenin that may promote NHEJ activity by increasing 53BP1 transcription, or by directly interacts with 53BP1. Aim 3 will determine if abnormal GSK3β activity determine brain tumor cell resistance to the prophylactic GSK3β-inhibition mediated protection from radiation induced cytotoxicity.


DNA damage response and repair in tumor resistance to treatment:

Glioblastoma (GBM) patients only survive an average of 15 months. Tumor resistance to radiation and other forms therapy is the leading challenge in GBM treatment. The mechanisms underlying GBM resistance to radiation therapy (RT) remain poorly understood and agents that selectively sensitize GBM to RT while sparing normal brain tissue are lacking. Pyruvate kinase M2 (PKM2) is the key cytoplasmic glycolytic enzyme, which is critical GBM tumor cell proliferation and expresses highly in cancer cells but minimally in normal brain tissue. Our laboratory has discovered a novel signaling network which connects the nuclear PKM2 function with homologous recombination (HR)-mediated repair of DNA double-strand breaks (DSBs) and GBM tumor cell resistance to radiation-induced cytotoxicity. Furthermore, our preliminary data revealed that PKM2 accumulates in the nucleus following irradiation and interacts with the critical HR rate-limiting protein, CtlP. Meanwhile, ataxia-telangiectasia mutated (ATM), the prime DNA-damage response protein kinase, phosphorylates PKM2 and regulates radiation-induced PKM2 nuclear accumulation and PKM2-depedent HR DSB repair. Therefore, we hypothesize that, in addition to controlling cytosolic glycolytic metabolism, nuclear PKM2 responds to novel upstream regulation by ATM to dictate the fate of irradiated GBM cells by promoting the repair of radiation-induced DSBs through enhanced CtIP-directed HR. A series of in vitro and in vivo experiments are proposed to test our hypotheses: Aim 1 will determine whether CtIP is a critical downstream functional target in PKM2-promotion of HR DSB repair and survival of irradiated GBM cells. Aim 2 will determine how ATM regulates PKM2 in HR DSB repair and subsequent GBM cell survival following radiation treatment. Aim 3 will determine whether targeting nuclear PKM2-dependent HR repair selectively sensitizes GBM tumor cells to DNA damage while sparing noncancerous brain cells in vitro and in vivo.

Impacts of host genetics in tumor development and cancer treatment:

Peripheral neuropathy is a set of symptoms caused by damage to the nerves that are distant from the brain and spinal cord. These distant nerves are called peripheral nerves. They carry sensations (feeling) to the brain and control the movement of our arms and legs. They also control the bladder and bowel. While chemotherapeutic drugs such as cisplatin are effective in killing cancer cells; they can also cause painful peripheral neuropathy (chemotherapy-induced peripheral neuropathy, [CIPN]). CIPN is one of the major health concerns for cancer patients. There are no effective remedies for CIPN. Therefore, new therapies that specifically target cancer cells while causing less CIPN are highly needed. Sirtuin 2 (Sirt2) is an enzyme expressed in many cells and tissues, with a high expression in the brain. Sirt2 has many effects by modifying other proteins in the cell. Our preliminary studies in cisplatin treated tumor-bearing mice have established a role for Sirt2 in both cancer development and CIPN.