Nucleocytoplasmic Shuttling of p62/SQSTM1 and Its Role in Recruitment of Nuclear Polyubiquitinated Proteins to Promyelocytic Leukemia Bodies

p62, also known as sequestosome1 (SQSTM1), A170, or ZIP, is a multifunctional protein implicated in several signal transduction pathways. p62 is induced by various forms of cellular stress, is degraded by autophagy, and acts as a cargo receptor for autophagic degradation of ubiquitinated targets. It is also suggested to shuttle ubiquitinated proteins for proteasomal degradation. p62 is commonly found in cytosolic protein inclusions in patients with protein aggregopathies, it is up-regulated in several forms of human tumors, and mutations in the gene are linked to classical adult onset Paget disease of the bone. To this end, p62 has generally been considered to be a cytosolic protein, and little attention has been paid to possible nuclear roles of this protein. Here, we present evidence that p62 shuttles continuously between nuclear and cytosolic compartments at a high rate. The protein is also found in nuclear promyelocytic leukemia bodies. We show that p62 contains two nuclear localization signals and a nuclear export signal. Our data suggest that the nucleocytoplasmic shuttling of p62 is modulated by phosphorylations at or near the most important nuclear localization signal, NLS2. The aggregation of p62 in cytosolic bodies also regulates the transport of p62 between the compartments. We found p62 to be essential for accumulation of polyubiquitinated proteins in promyelocytic leukemia bodies upon inhibition of nuclear protein export. Furthermore, p62 contributed to the assembly of proteasome-containing degradative compartments in the vicinity of nuclear aggregates containing polyglutamine-expanded Ataxin1Q84 and to the degradation of Ataxin1Q84.     

Phosphorylation of mCRY2 at Ser557 in the Hypothalamic Suprachiasmatic Nucleus of the Mouse

Cryptochrome1 and 2 play a critical role in the molecular oscillations of the circadian clocks of central and peripheral tissues in mammals. Mouse Cryptochrome2 (mCRY2) is phosphorylated at Ser557 in the liver, in which the Ser557-phosphorylated form accumulates during the night in parallel with mCRY2 protein. Phosphorylation of mCRY2 at Ser557 allows subsequent phosphorylation at Ser553 by glycogen synthase kinase-3β (GSK-3β), resulting in efficient degradation of mCRY2 by a proteasome pathway. In the present study, we found that mCRY2 is phosphorylated at Ser557 also in the region of the mouse brain containing the suprachiasmatic nucleus (SCN), the central circadian clock tissue. Daily fluctuation of the Ser557-phosphorylation level in the SCN region suggests an important role of sequential phosphorylation of Ser557 and Ser553 in the rhythmic degradation of mCRY2 in both central and peripheral clocks of mice.     

The possible involvement of endogenous ligands for mu-, delta- and kappa-opioid receptors in modulating morphine-induced CPP expression in rats

Previous studies suggested that electroacupuncture (EA) can suppress opioid dependence by the release of endogenous opioid peptides. To explore the site of action and the receptors involved, we tried to inject highly specific agonists for μ-, δ- and κ-opioid receptors into the CNS to test whether it can suppress morphine-induced conditioned place preference (CPP) in the rat. Male Sprague–Dawley rats were trained with 4 mg/kg morphine, i.p. for 4 days to establish the CPP model. This CPP can be prevented by (a) i.p. injection of 3 mg/kg dose of morphine, (b) intracerebroventricular (i.c.v.) injection of micrograms doses of the selective μ-opioid receptor agonist DAMGO, δ-agonist DPDPE or κ-agonist U-50,488H or (c) microinjection of DAMGO, DPDPE or U50488H into the shell of the nucleus accumbens (NAc). The results suggest that the release of endogenous μ-, δ- and κ-opioid agonists in the NAc shell may play a role for EA suppression of opiate addiction.     

Comparison of cellular response in bovine intervertebral disc cells and articular chondrocytes: effects .of lipopolysaccharide on proteoglycan metabolism

Lipopolysaccharide (LPS) induces matrix degradation and markedly stimulates the production of several cytokines, i.e., interleukin-1β, −6, and −10, by disc cells and chondrocytes. We performed a series of experiments to compare cellular responses of cells from the bovine intervertebral disc (nucleus pulposus and annulus fibrosus) and from bovine articular cartilage to LPS. Alginate beads containing cells isolated from bovine intervertebral discs and articular cartilage were cultured with or without LPS in the presence of 10% fetal bovine serum. The DNA content and the rate of proteoglycan synthesis and degradation were determined. In articular chondrocytes, LPS strongly suppressed cell proliferation and proteoglycan synthesis in a dose-dependent manner and stimulated proteoglycan degradation. Compared with articular chondrocytes, nucleus pulposus cells responded in a similar, although less pronounced manner. However, treatment of annulus fibrosus cells with LPS showed no significant effects on proteoglycan synthesis or degradation. A slight, but statistically significant, inhibition of cell proliferation was observed at high concentrations of LPS in annulus fibrosus cells. Thus, LPS suppressed proteoglycan synthesis and stimulated proteoglycan degradation by articular chondrocytes and nucleus pulposus cells. The effects of LPS on annulus fibrosus cells were minor compared with those on the other two cell types. The dissimilar effects of LPS on the various cell types suggest metabolic differences between these cells and may further indicate a divergence in pathways of LPS signaling and a differential sensitivity to exogenous stimuli such as LPS.This work was supported in part by NIH grants 2-P50-AR39239 and 1-P01-AR48152.     

The Rothmund-Thomson gene product RECQL4 localizes to the nucleolus in response to oxidative stress

Mutations in the RECQL4 helicase gene have been linked to Rothmund-Thomson syndrome (RTS), which is characterized by poikiloderma, growth deficiency, and a predisposition to cancer. Examination of RECQL4 subcellular localization in live cells demonstrated a nucleoplasmic pattern and, to a lesser degree, staining in nucleoli. Analysis of RECQL4-GFP deletion mutants revealed two nuclear localization regions in the N-terminal region of RECQL4 and a nucleolar localization signal at amino acids 376-386. RECQL4 localization did not change after treatment with the DNA-damaging agents bleomycin, etoposide, UV irradiation and gamma irradiation, in contrast to the Bloom and Werner syndrome helicases that relocate to distinct nuclear foci after damage. However, in a significant number of cells exposed to hydrogen peroxide or streptonigrin, RECQL4 accumulated in nucleoli. Using a T7 phage display screen, we determined that RECQL4 interacts with poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme that promotes genomic integrity through its involvement in DNA repair and signaling pathways. The RECQL4 nucleolar localization was inhibited by pretreatment with a PARP-1 inhibitor. The C-terminal portion of RECQL4 was found to be an in vitro substrate for PARP-1. These results demonstrate changes in the intracellular localization of RECQL4 in response to oxidative stress and identify an interaction between RECQL4 and PARP-1.     

Nanosecond pulsed electric fields cause melanomas to self-destruct

We have discovered a new, drug-free therapy for treating solid skin tumors. Pulsed electric fields greater than 20 kV/cm with rise times of 30 ns and durations of 300 ns penetrate into the interior of tumor cells and cause tumor cell nuclei to rapidly shrink and tumor blood flow to stop. Melanomas shrink by 90% within two weeks following a cumulative field exposure time of 120 micros. A second treatment at this time can result in complete remission. This new technique provides a highly localized targeting of tumor cells with only minor effects on overlying skin. Each pulse deposits 0.2 J and 100 pulses increase the temperature of the treated region by only 3 degrees C, ten degrees lower than the minimum temperature for hyperthermia effects.