In JoVE (1)

Other Publications (6)

Articles by Jin I. Lee in JoVE

Other articles by Jin I. Lee on PubMed

Association Between Lifestyle Factors and CpG Island Methylation in a Cancer-free Population

Cancer Epidemiology, Biomarkers & Prevention : a Publication of the American Association for Cancer Research, Cosponsored by the American Society of Preventive Oncology. Nov, 2009  |  Pubmed ID: 19861513

Many risk factors have been associated with cancer, such as age, family history, race, smoking, high-fat diet, and poor nutrition. It is important to reveal the molecular changes related to risk factors that could facilitate early detection, prevention, and overall control of cancer.

Regulators of AWC-mediated Olfactory Plasticity in Caenorhabditis Elegans

PLoS Genetics. Dec, 2009  |  Pubmed ID: 20011101

While most sensory neurons will adapt to prolonged stimulation by down-regulating their responsiveness to the signal, it is not clear which events initiate long-lasting sensory adaptation. Likewise, we are just beginning to understand how the physiology of the adapted cell is altered. Caenorhabditis elegans is inherently attracted to specific odors that are sensed by the paired AWC olfactory sensory neurons. The attraction diminishes if the animal experiences these odors for a prolonged period of time in the absence of food. The AWC neuron responds acutely to odor-exposure by closing calcium channels. While odortaxis requires a Galpha subunit protein, cGMP-gated channels, and guanylyl cyclases, adaptation to prolonged odor exposure requires nuclear entry of the cGMP-dependent protein kinase, EGL-4. We asked which candidate members of the olfactory signal transduction pathway promote nuclear entry of EGL-4 and which molecules might induce long-term adaptation downstream of EGL-4 nuclear entry. We found that initiation of long-term adaptation, as assessed by nuclear entry of EGL-4, is dependent on G-protein mediated signaling but is independent of fluxes in calcium levels. We show that long-term adaptation requires polyunsaturated fatty acids (PUFAs) that may act on the transient receptor potential (TRP) channel type V OSM-9 downstream of EGL-4 nuclear entry. We also present evidence that high diacylglycerol (DAG) levels block long-term adaptation without affecting EGL-4 nuclear entry. Our analysis provides a model for the process of long-term adaptation that occurs within the AWC neuron of C. elegans: G-protein signaling initiates long-lasting olfactory adaptation by promoting the nuclear entry of EGL-4, and once EGL-4 has entered the nucleus, processes such as PUFA activation of the TRP channel OSM-9 may dampen the output of the AWC neuron.

Nuclear Entry of a CGMP-dependent Kinase Converts Transient into Long-lasting Olfactory Adaptation

Proceedings of the National Academy of Sciences of the United States of America. Mar, 2010  |  Pubmed ID: 20220099

To navigate a complex and changing environment, an animal's sensory neurons must continually adapt to persistent cues while remaining responsive to novel stimuli. Long-term exposure to an inherently attractive odor causes Caenorhabditis elegans to ignore that odor, a process termed odor adaptation. Odor adaptation is likely to begin within the sensory neuron, because it requires factors that act within these cells at the time of odor exposure. The process by which an olfactory sensory neuron makes a decisive shift over time from a receptive state to a lasting unresponsive one remains obscure. In C. elegans, adaptation to odors sensed by the AWC pair of olfactory neurons requires the cGMP-dependent protein kinase EGL-4. Using a fully functional, GFP-tagged EGL-4, we show here that prolonged odor exposure sends EGL-4 into the nucleus of the stimulated AWC neuron. This odor-induced nuclear translocation correlates temporally with the stable dampening of chemotaxis that is indicative of long-term adaptation. Long-term adaptation requires cGMP binding residues as well as an active EGL-4 kinase. We show here that EGL-4 nuclear accumulation is both necessary and sufficient to induce long-lasting odor adaptation. After it is in the AWC nucleus, EGL-4 decreases the animal's responsiveness to AWC-sensed odors by acting downstream of the primary sensory transduction. Thus, the EGL-4 protein kinase acts as a sensor that integrates odor signaling over time, and its nuclear translocation is an instructive switch that allows the animal to ignore persistent odors.

Changes in CGMP Levels Affect the Localization of EGL-4 in AWC in Caenorhabditis Elegans

PloS One. 2012  |  Pubmed ID: 22319638

The Protein Kinase G, EGL-4, is required within the C. elegans AWC sensory neurons to promote olfactory adaptation. After prolonged stimulation of these neurons, EGL-4 translocates from the cytosol to the nuclei of the AWC. This nuclear translocation event is both necessary and sufficient for adaptation of the AWC neuron to odor. A cGMP binding motif within EGL-4 and the Gα protein ODR-3 are both required for this translocation event, while loss of the guanylyl cyclase ODR-1 was shown to result in constitutively nuclear localization of EGL-4. However, the molecular changes that are integrated over time to produce a stably adapted response in the AWC are unknown. Here we show that odor-induced fluctuations in cGMP levels in the adult cilia may be responsible in part for sending EGL-4 into the AWC nucleus to produce long-term adaptation. We found that reductions in cGMP that result from mutations in the genes encoding the cilia-localized guanylyl cyclases ODR-1 and DAF-11 result in constitutively nuclear EGL-4 even in naive animals. Conversely, increases in cGMP levels that result from mutations in cGMP phosphodiesterases block EGL-4 nuclear entry even after prolonged odor exposure. Expression of a single phosphodiesterase in adult, naive animals was sufficient to modestly increase the number of animals with nuclear EGL-4. Further, coincident acute treatment of animals with odor and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) decreased the number of animals with nuclear EGL-4. These data suggest that reducing cGMP levels in AWC is necessary and even partially sufficient for nuclear translocation of EGL-4 and adaptation as a result of prolonged odor exposure. Our genetic analysis and chemical treatment of C. elegans further indicate that cilia morphology, as defined by fluorescent microscopic observation of the sensory endings, may allow for odor-induced fluctuations in cGMP levels and this fluctuation may be responsible for sending EGL-4 into the AWC nucleus.

The Integral Membrane Protein ITM2A, a Transcriptional Target of PKA-CREB, Regulates Autophagic Flux Via Interaction with the Vacuolar ATPase

Autophagy. 2015  |  Pubmed ID: 25951193

The PKA-CREB signaling pathway is involved in many cellular processes including autophagy. Recent studies demonstrated that PKA-CREB inhibits autophagy in yeast; however, the role of PKA-CREB signaling in mammalian cell autophagy has not been fully characterized. Here, we report that the integral membrane protein ITM2A expression is positively regulated by PKA-CREB signaling and ITM2A expression interferes with autophagic flux by interacting with vacuolar ATPase (v-ATPase). The ITM2A promoter contains a CRE element, and mutation at the CRE consensus site decreases the promoter activity. Forskolin treatment and PKA expression activate the ITM2A promoter confirming that ITM2A expression is dependent on the PKA-CREB pathway. ITM2A expression results in the accumulation of autophagosomes and interferes with autolysosome formation by blocking autophagic flux. We demonstrated that ITM2A physically interacts with v-ATPase and inhibits lysosomal function. These results support the notion that PKA-CREB signaling pathway regulates ITM2A expression, which negatively regulates autophagic flux by interfering with the function of v-ATPase.

The Anti-hypertensive Drug Reserpine Induces Neuronal Cell Death Through Inhibition of Autophagic Flux

Biochemical and Biophysical Research Communications. Jul, 2015  |  Pubmed ID: 25976674

Reserpine is a well-known medicine for the treatment of hypertension and schizophrenia, but its administration can induce Parkinson's disease (PD)-like symptoms in humans and animals. Reserpine inhibits the vesicular transporter of monoamines and depletes the brain of monoamines such as dopamine. However, the cellular function of reserpine is not fully understood. In this report, we present one possible mechanism by which reserpine may contribute to PD-like symptoms. Reserpine treatment induced the formation of enlarged autophagosomes by inhibiting the autophagic flux and led to accumulation of p62, an autophagy adapter molecule. In particular, reserpine treatment increased the level of α-synuclein protein and led to accumulation of α-synuclein in autophagosomes. Treatment with rapamycin enhanced the effect of reserpine by further increasing the level of α-synuclein and neuronal cell death. Drosophila raised on media containing reserpine showed loss of dopaminergic neurons. Furthermore, cotreatment with reserpine and rapamycin aggravated the loss of dopaminergic neurons. Our results suggest that reserpine contributes to the loss of dopaminergic neurons by interfering with autophagic flux.

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