Histone methyltransferase SUV39H1 regulates the Golgi complex via the nuclear envelope-spanning LINC complex.

Cell motility is related to the higher-order structure of chromatin. Stimuli that induce cell migration change chromatin organization; such stimuli include elevated histone H3 lysine 9 trimethylation (H3K9me3). We previously showed that depletion of histone H3 lysine 9 methyltransferase, SUV39H1, suppresses directional cell migration. However, the molecular mechanism underlying this association between chromatin and cell migration remains elusive. The Golgi apparatus is a cell organelle essential for cell motility. In this study, we show that loss of H3K9 methyltransferase SUV39H1 but not SETDB1 or SETDB2 causes dispersion of the Golgi apparatus throughout the cytoplasm. The Golgi dispersion triggered by SUV39H1 depletion is independent of transcription, centrosomes, and microtubule organization, but is suppressed by depletion of any of the following three proteins: LINC complex components SUN2, nesprin-2, or microtubule plus-end-directed kinesin-like protein KIF20A. In addition, SUN2 is closely localized to H3K9me3, and SUV39H1 affects the mobility of SUN2 in the nuclear envelope. Further, inhibition of cell motility caused by SUV39H1 depletion is restored by suppression of SUN2, nesprin-2, or KIF20A. In summary, these results show the functional association between chromatin organization and cell motility via the Golgi organization regulated by the LINC complex.

The LINC Complex Assists the Nuclear Import of Mechanosensitive Transcriptional Regulators.

Mechanical forces play pivotal roles in directing cell functions and fate. To elicit gene expression, either intrinsic or extrinsic mechanical information are transmitted into the nucleus beyond the nuclear envelope via at least two distinct pathways, possibly more. The first and well-known pathway utilizes the canonical nuclear transport of mechanoresponsive transcriptional regulators through the nuclear pore complex, which is an exclusive route for macromolecular trafficking between the cytoplasm and nucleoplasm. The second pathway depends on the linker of the nucleoskeleton and cytoskeleton (LINC) complex, which is a molecular bridge traversing the nuclear envelope between the cytoskeleton and nucleoskeleton. This protein complex is a central component in mechanotransduction at the nuclear envelope that transmits mechanical information from the cytoskeleton into the nucleus to influence the nuclear structure, nuclear stiffness, chromatin organization, and gene expression. Besides the mechanical force transducing function, recent increasing evidence shows that the LINC complex plays a role in controlling nucleocytoplasmic transport of mechanoresponsive transcriptional regulators. Here we discuss recent findings regarding the contribution of the LINC complex to the regulation of intracellular localization of the most-notable mechanosensitive transcriptional regulators, ß-catenin, YAP, and TAZ.

Inhibitory activity of flavonoids from Ephedrae Herba on hypoxia signaling in PANC-1 cells and the evaluation of their mechanisms.

Pancreatic cancer is a lethal disease with a very poor prognosis. Recent reports indicate that hypoxia signaling mediated by hypoxia-inducible factor (HIF) contributes to the progression of pancreatic cancer. Therefore, elucidating the inhibitor of hypoxia signaling may lead to the development of a candidate for new anticancer agents. During our screening program for HIF inhibitor from crude drug extracts, new acylated kaempferol glycosides, kaempferol 3-O-[4″-(E)-p-coumaroyl-3″-O-dihydroxypalmityl] rhamnoside (1) and kaempferol 3-O-[4″-(E)-p-coumaroyl-2″-O-dihydroxypalmityl] rhamnoside (2), were isolated from an acetone extract of Ephedrae Herba, together with eight known flavonol glycosides (3-10). The structures of novel compounds 1 and 2 were elucidated based on spectroscopic and chemical analyses. Using a cell-based HRE-driven luciferase reporter assay in a PANC-1 pancreatic cancer cell line, we found that these compounds demonstrated potent inhibitory activity on hypoxia signaling with IC50 values of 18.0 ± 0.6 and 13.3 ± 2.2 µM, respectively. Mechanistically, 2 reduced the amount of HIF-1α protein in the nuclear at 30 µM via the ubiquitin-proteasome pathway with no effect on the nuclear translocation of HIF proteins from cytosol and subsequently decreased Glut1 mRNA. These results indicate that 2 inhibits hypoxia signaling through a mechanism involving the reduction of HIF-1α protein levels and Glut1 mRNA and may have anti-pancreatic cancer effects.

Triiodothyronine enhances accumulation of intracellular lipids in adipocytes through thyroid hormone receptor α via direct and indirect mechanisms.

Triiodothyronine (T3) enhanced the expression of adipogenic and lipogenic genes with elevation of the intracellular lipids through thyroid hormone receptor (TR) α in mouse 3T3-L1 cells. However, the transcription of the SREBP-1c and HSL genes was decreased by T3. Such T3-mediated alterations were negated by TRα siRNA. Chromatin immunoprecipitation assay showed that the binding of TRα to the TR-responsive element (TRE) of the FAS promoter was elevated by T3. In contrast, the ability of TRα to bind to the TRE of the SREBP-1c promoter was decreased by T3. In addition, the binding of SREBP-1c to the SRE of the HSL promoter was lowered by T3. These results indicate that T3 increased the accumulation of intracellular lipids by enhancing the expression of the FAS gene through direct binding of TRα to the FAS promoter and simultaneously lowered the amount of lipolysis via reduced binding of T3-decreased SREBP-1c to the HSL promoter.