Faculty Bibliography

All mammalian eggs are surrounded by a relatively thick extracellular coat, the zona pellucida, that plays vital roles during oogenesis, fertilization, and preimplantation development. The mouse zona pellucida consists of three glycoproteins that are synthesized solely by growing oocytes and assemble into long fibrils that constitute a matrix. Zona pellucida glycoproteins are responsible for species-restricted binding of sperm to unfertilized eggs, inducing sperm to undergo acrosomal exocytosis, and preventing sperm from binding to fertilized eggs. Many features of mammalian and non-mammalian egg coat polypeptides have been conserved during several hundred million years of evolution.

As axons myelinate, establish a stable neurofilament network, and expand in caliber, neurofilament proteins are extensively phosphorylated along their C-terminal tails, which is recognized by the monoclonal antibody, RT-97. Here, we demonstrate in vivo that RT-97 immunoreactivity (IR) is generated by phosphorylation at KSPXK or KSPXXXK motifs and requires flanking lysines at specific positions. extracellular signal regulated kinase 1,2 (ERK1,2) and pERK1,2 levels increase in parallel with phosphorylation at the RT-97 epitope during early postnatal brain development. Purified ERK1,2 generated RT-97 on both KSP motifs on recombinant NF-H tail domain proteins, while cdk5 phosphorylated only KSPXK motifs. RT-97 epitope generation in primary hippocampal neurons was regulated by extensive cross-talk among ERK1,2, c-Jun N-terminal kinase 1,2 (JNK1,2) and cdk5. Inhibition of both ERK1,2 and JNK1,2 completely blocked RT-97 generation. Cdk5 influenced RT-97 generation indirectly by modulating JNK activation. In mice, cdk5 gene deletion did not significantly alter RT-97 IR or ERK1,2 and JNK activation. In mice lacking the cdk5 activator P35, the partial suppression of cdk5 activity increased RT-97 IR by activating ERK1,2. Thus, cdk5 influences RT-97 epitope generation partly by modulating ERKs and JNKs, which are the two principal kinases regulating neurofilament phosphorylation. The regulation of a single target by multiple protein kinases underscores the importance of monitoring other relevant kinases when the activity of a particular one is blocked.

The N-ribosyldihydronicotinamide (NRH):quinone oxidoreductase 2 (NQO2) gene encodes an enzyme that catalyzes activation of quinones. Blood DNA from 80 control individuals and 118 age-matched Parkinson's disease patients were analyzed for NQO2 gene promoter polymorphisms. The results revealed three allelic variants, designated I-29, I-16, and D. These results were confirmed in fibroblast cell lines. In patients with Parkinson's disease, there was a significant increase in the frequency of the D allele, but there was no difference in the frequency of the alleles in familial compared to sporadic Parkinson's disease. The D and I-16 promoters direct higher NQO2 gene expression that results in higher enzyme activity. Overexpression of NQO2 in the catecholaminergic neuroblastoma SH-SY5Y cells resulted in increased production of reactive oxygen species when exposed to exogenous dopamine. The results suggest that the association of the D promoter with Parkinson's disease may be due to an increase in expression of the NQO2 gene.

Metastasis comprises several subsequent steps including local invasion and intravasation at the primary site, then their adhesion/arrest within the vessels of host organs followed by their extravasation and infiltration into the target organ stroma. In contrast to previous studies which have used aspartate-glycine-arginine (RGD) peptides and antibodies against integrins, we used rare collagen- and laminin-antagonizing integrin inhibitors from snake venoms to analyze the colonization of the liver by tumor cells both by intravital microscopy and in vitro. Adhesion of liver-targeting tumor cells to the sinusoid wall components, laminin-1 and fibronectin, is essential for liver metastasis. This step is inhibited by lebein-1, but not by lebein-2 or rhodocetin. Both lebeins from the Vipera lebetina venom block integrin interactions with laminins in an RGD-independent manner. Rhodocetin is an antagonist of alpha2beta1 integrin, a collagen receptor on many tumor cells. Subsequent to tumor cell arrest, extravasation into the liver stroma and micrometastasis are efficiently delayed by rhodocetin. This underlines the importance of alpha2beta1 integrin interaction with the reticular collagen I-rich fibers in liver stroma. Antagonists of laminin- and collagen-binding integrins could be valuable tools to individually block the direct interactions of tumor cells with distinct matrix components of the Disse space, thereby reducing liver metastasis.

NAD(P)H:quinone oxidoreductase 1 null (NQO1(-/-)) mice exposed to 3 Gy of gamma-radiation showed an increase in neutrophils, bone marrow hypercellularity, and enlarged lymph nodes and spleen. The spleen showed disrupted follicular structure, loss of red pulp, and granulocyte and megakarocyte invasion. Blood and histologic analysis did not show any sign of infection in mice. These results suggested that exposure of NQO1(-/-) mice to gamma-radiation led to myeloproliferative disease. Radiation-induced myeloproliferative disease was observed in 74% of NQO1(-/-) mice as compared with none in wild-type (WT) mice. NQO1(-/-) mice exposed to gamma-radiation also showed lymphoma tissues (32%) and lung adenocarcinoma (84%). In contrast, only 11% WT mice showed lymphoma and none showed lung adenocarcinoma. Exposure of NQO1(-/-) mice to gamma-radiation resulted in reduced apoptosis in granulocytes and lack of induction of p53, p21, and Bax. NQO1(-/-) mice also showed increased expression of myeloid differentiation factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and Pu.1. Intriguingly, exposure of NQO1(-/-) mice to gamma-radiation failed to induce C/EBPalpha and Pu.1, as was observed in WT mice. These results suggest that decreased p53/apoptosis and increased Pu.1 and C/EBPalpha led to myeloid hyperplasia in NQO1(-/-) mice. The lack of induction of apoptosis and differentiation contributed to radiation-induced myeloproliferative disease in NQO1(-/-) mice.

Promyelocytic leukemia zinc finger (PLZF) is a transcriptional repressor and tumor suppressor inhibiting melanoma cell growth in vitro and in vivo in animal models. In this study, we analyzed the impact of in vivo primary tumor gene expression of PLZF on the long-term survival of malignant melanoma patients. PLZF expression was assessed by using DNA microarray and real-time polymerase chain reaction analysis of 41 primary malignant melanomas from patients with a defined histology and a close to 20-year clinical follow-up, of 29 melanoma metastases, and of 6 different melanoma cell lines. Kaplan-Meier survival analyses, log-rank statistics and Cox regression analysis were employed to identify the impact of PLZF expression on long-term survival. We detected PLZF expression in 92% of primary melanoma tumors in vivo but not in melanoma cell lines in vitro. By univariate analysis, we identified: (1) PLZF mRNA expression < or = 10,000 mRNA copies/mug total tumor RNA, (2) Breslow tumor thickness >4 mm, and (3) American Joint Committee on Cancer stages IIC, IIIB, IIIC, and IV as statistically significant pretreatment risk factors. We defined a continuous prognostic index (i.e., risk score) for primary melanoma patients based on the regression coefficient of PLZF mRNA expression. Applying a cutpoint to the prognostic index at - 1.65, patients were assigned to one of two risk groups: low-risk patients (n = 28) with a median overall survival of 79 months (5-year survival of 61%) and high-risk patients (n = 13) with a median overall survival of 32 months (5-year survival of 23%) (p < 0.05). This is the first time that PLZF mRNA expression has been linked to a prognostic model for primary malignant melanoma patients to derive prognostic groups for clinical purposes (e.g., improved melanoma immunotherapies).

Vitamin K1, K2, and K3 are essential nutrients associated with blood clotting and bone metabolism. Quinone oxidoreductases [NAD(P)H:quinone oxidoreductase 1 (NQO1) and NRH:quinone oxidoreductase 2 (NQO2)] are among the selected enzymes that catalyze reduction of vitamin K to vitamin K hydroquinone. NQO1 catalyzes high affinity reduction of vitamin K3 but has only weak affinity for reduction of vitamin K1 and K2. Vitamin K hydroquinone serves as a cofactor for vitamin K gamma-carboxylase that catalyzes gamma-carboxylation of specific glutamic acid residues in Gla-factors/proteins leading to their activation and participation in blood clotting and bone metabolism. Concomitant with Gla modification, a reduced vitamin K molecule is converted to vitamin K epoxide, which is converted back to vitamin K by the enzyme vitamin K epoxide reductase to complete vitamin K cycle. Vitamin K is also redox cycled. One-electron reduction of vitamin K3 leads to the formation of semiquinone that in the presence of oxygen is oxidized back to vitamin K3. Oxygen is reduced to generate reactive oxygen species (ROS) that causes oxidative stress and cytotoxicity. Vitamin K is used as radiation sensitizer or in mixtures with other chemotherapeutic drugs to treat several types of cancer. ROS generated in redox cycling contributes to anticancer activity of vitamin K. NQO1 competes with enzymes that redox cycle vitamin K and catalyzes two-electron reduction of vitamin K3 to hydroquinone. This skips formation of semiquinone and ROS. Therefore, NQO1 metabolically detoxifies vitamin K3 and protects cells against oxidative stress and other adverse effects. On the contrary, NQO2 catalyzes metabolic activation of vitamin K3 leading to cytotoxicity. The role of NQO1 and NQO2 in metabolic detoxification and/or activation of vitamin K1 and K2 remains to be determined. Future studies are also required to identify the enzymes that catalyze high affinity reduction of vitamin K1 and K2 to hydroquinone for use in gamma-carboxylation reactions.

Glucose-regulated GRP58 has shown clinical applications to endoplasmic reticulum (ER) stress and cancer. GRP58 is localized in the cytosol, endoplasmic reticulum (ER) and nucleus. Twenty-four amino acids at the N-terminal hydrophobic region are known to target GRP58 to ER for synthesis at the ER membrane and translocation into the ER lumen. In addition, GRP58 contains putative nuclear localization (494KPKKKKK500) and ER retention (502QEDL505) signals. However, the role of these signals in nuclear import and ER retention of GRP58 remains unknown. Present studies investigated the signals that control nuclear localization and ER retention of GRP58. Deletion/mutation of nuclear localization signal (NLS) abrogated nuclear import of GRP58. NLS attached to EGFP localized EGFP in the nucleus. However, deletion/mutation of putative ER retention signal alone did not alter ER retention of GRP58. Interestingly, a combined deletion/mutation of NLS and ER retention signals blocked the GRP58 retention in the ER. These results concluded that overlapping NLS and ER retention signal sequences regulate nuclear localization and ER retention of GRP58.

INrf2-Nrf2 proteins are sensors of chemical/radiation stress. Nrf2, in response to stresses, is released from INrf2. Nrf2 is translocated into the nucleus where it binds to the antioxidant response element and coordinately activates the expression of a battery of genes that protect cells against oxidative and electrophilic stress. An autoregulatory loop between INrf2 and Nrf2 regulates their cellular abundance. Nrf2 activates INrf2 gene expression, and INrf2 serves as an adapter for degradation of Nrf2. In this report, we demonstrate that mutation of tyrosine 141 in bric-a-bric, tramtrack, broad complex domain to alanine rendered INrf2 unstable and nonfunctional. INrf2Y141A mutant degraded rapidly as compared with wild type INrf2, although it could dimerize and bind Nrf2. De novo synthesized INrf2 protein was phosphorylated at tyrosine 141. Tyrosine 141-phosphorylated INrf2 was highly stable. Treatment with hydrogen peroxide, which is an oxidizing agent, led to dephosphorylation of INrf2Y141, resulting in rapid degradation of INrf2. This resulted in stabilization of Nrf2 and activation of ARE-mediated gene expression. These results demonstrate that stress-induced dephosphorylation of tyrosine 141 is a novel mechanism in Nrf2 activation and cellular protection.