EGCG-induced selective death of cancer cells through autophagy-dependent regulation of the p62-mediated antioxidant survival pathway

The effects of EGCG on the selective death of cancer cells by modulating antioxidant pathways through autophagy were explored in various normal and cancer cells. EGCG positively regulated the p62-KEAP1-NRF2-HO-1 pathway in normal cells, while negatively regulating it in cancer cells, leading to selective apoptotic death of cancer cells. In EGCG-treated MRC5 cells (EGCG-MRC5), autophagic flux was blocked, which was accompanied by the formation of p62-positive aggregates. However, EGCG-treated HeLa cells (EGCG-HeLa) showed incomplete autophagic flux and no aggregate formation. The levels of P-ULK1 S556 and S758 increased in EGCG-MRC5 through AMPK-mTOR cooperative interaction. In contrast, EGCG treatment in HeLa cells led to AMPK-induced mTOR inactivation, resulting in abrogation of P-ULK1 S556 and S758 levels. AMPK knockout in EGCG-HeLa restored positive regulation of the p62-mediated pathway, which was accompanied by increased P-mTOR S2448 and P-ULK1 S758 levels. Knockdown of 67LR in EGCG-HeLa abolished AMPK activity but did not restore the p62-mediated pathway. Surprisingly, both AMPK knockout and 67LR knockdown in EGCG-HeLa markedly increased cell viability, despite differential regulation of the antioxidant enzyme HO-1. In conclusion, EGCG induces the selective death of cancer cells through the modulation of at least two autophagy-dependent and independent regulatory pathways: negative regulation involves the mTOR-ULK1 (S556 and S758)-p62-KEAP1-NRF2-HO-1 axis via AMPK activation, whereas positive regulation occurs through the 67LR-AMPK axis.

Leukocyte telomere length is independently associated with gait speed in elderly women

OBJECTIVES

Declining gait speed is common in the elderly population and is associated with age-related conditions. Because telomere length is a reflection of aging and known to affect degenerative changes in organ systems, gait speed may be associated with telomere length. We therefore investigated the relationship between gait speed and leukocyte telomere length in elderly Korean women.

STUDY DESIGN

Cross-sectional study.

MAIN OUTCOME MEASURES

A total of 117 Korean elderly women participated. Metabolic variables were assessed along with gait speed calculated as walking distance (6m) divided by time. Leukocyte telomere length was measured by real-time quantitative polymerase chain reaction.

RESULTS

Gait speed correlated with telomere length (r=0.38, p<0.01), fasting insulin (r=-0.19, p=0.04), homeostasis model assessment of insulin resistance index (HOMA-IR; r=-0.22, p=0.02), triglyceride (r=-0.20, p=0.03), and Korean Mini-Mental State Examination (K-MMSE; r=0.20, p=0.03) after adjusting for age. On step-wise multiple regression analysis, telomere length (β=0.35, p<0.01), K-MMSE (β=0.16, p=0.02), age (β=-0.23, p=0.01), and HOMA-IR (β=-0.19, p=0.03) were identified as independent variables associated with gait speed.

CONCLUSIONS

This study suggested that telomere length may have a role in maintaining overall health status as well as preserving gait speed in the elderly population. Further studies are required to better understand the significance of our findings.

Delayed rectifier potassium currents induced in activated rat microglia set the resting membrane potential

The delayed rectifying outward K+ (IK) current was measured in lipopolysaccharide (LPS)-activated cultured rat microglial cells by using whole-cell patch clamp method. The current showed 'window current' where channels were available for activation but never fully inactivated. At near resting membrane potential some part of the current was able to be activated by depolarization. Among the several K+ channel blockers tested, only 4-aminopyridine (4-AP) was able to block most of the current and depolarize the membrane potential reversibly. These results suggest that 4-AP sensitive IK current plays a direct role of setting the resting membrane potential in LPS-activated microglia.

Modulation of large conductance Ca2+-activated K+ channel by Galphah (transglutaminase II) in the vascular smooth muscle cell

Among G-proteins, Gh is unique in structural differences in the GTP-binding domain and possessing transglutaminase activity. We have studied the role of G protein in modulation of large conductance Ca2+-activated K+ (Maxi-K+) channel by the inside-out mode of patch clamp in smooth muscle cells from superior mesenteric artery of the rabbit. When the non-hydrolyzable GTP analogue, GTPgammaS, was applied, the channel activity was increased about 2.5-fold. Addition of GDPbetaS resulted in reversal of the GTPgammaS effect. When the Galphah7 antibody was applied, the GTPgammaS-stimulated channel activity was significantly inhibited to control level, suggesting that Galphah is involved in activation of the Maxi-K+ channel in smooth muscle cells.

Modulation of large conductance calcium-activated K+ channel by membrane-delimited protein kinase and phosphatase activities

Large conductance Ca(2+)-activated K+ channel was identified and studied in excised inside-out membrane patches of freshly dispersed smooth muscle cells from rabbit gastric antrum. The current-voltage relationship of the single channel was linear from -80 to +80 mV of pipette voltage in which single channel conductance was 249 +/- 17.8 pS (n = 19) in symmetrical concentration of K+ (145 mM) across the patch. Activity of the channel (NPo) depended not only on cytoplasmic calcium concentration but also on membrane potential. MgATP increased NPo in a dose-dependent manner and Mg2+ was prerequisite for the effect. Okadaic acid (100 nM), inhibitor of protein phosphatases, increased NPo further in the presence of MgATP. Therefore, it would be concluded that activity of the calcium-activated K+ channel in gastric smooth muscle cells was controlled by phosphorylation state of the channel protein and the state is further modulated by membrane-delimited protein kinase and protein phosphatase activities.