Intramolecular interaction in LGN, an adaptor protein that regulates mitotic spindle orientation.

Proper mitotic spindle orientation requires that astral microtubules are connected to the cell cortex by the microtubule-binding protein NuMA, which is recruited from the cytoplasm. Cortical recruitment of NuMA is at least partially mediated via direct binding to the adaptor protein LGN. LGN normally adopts a closed conformation via an intramolecular interaction between its N-terminal NuMA-binding domain and its C-terminal region that contains four GoLoco (GL) motifs, each capable of binding to the membrane-anchored Gαi subunit of heterotrimeric G protein. Here we show that the intramolecular association with the N-terminal domain in LGN involves GL3, GL4, and a region between GL2 and GL3, whereas GL1 and GL2 do not play a major role. This conformation renders GL1 but not the other GL motifs in a state easily accessible to Gαi To interact with full-length LGN in a closed state, NuMA requires the presence of Gαi; both NuMA and Gαi are essential for cortical recruitment of LGN in mitotic cells. In contrast, mInsc, a protein that competes with NuMA for binding to LGN and regulates mitotic spindle orientation in asymmetric cell division, efficiently binds to full-length LGN without Gαi and induces its conformational change, enhancing its association with Gαi In nonpolarized symmetrically dividing HeLa cells, disruption of the LGN-NuMA interaction by ectopic expression of mInsc results in a loss of cortical localization of NuMA during metaphase and anaphase and promotes mitotic spindle misorientation and a delayed anaphase progression. These findings highlight a specific role for LGN-mediated cell cortex recruitment of NuMA.

FIB-4 Index and Liver Stiffness Measurement are Potential Predictors of Atherosclerosis in Metabolic Dysfunction-Associated Steatotic Liver Disease.

AIMS: Cardiovascular disease (CVD) is a common cause of death in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). Therefore, CVD surveillance is important, but it is not well established. We evaluated the association between liver fibrosis, carotid artery atherosclerosis, and coronary artery stenosis in patients with MASLD. METHODS: Overall, 153 patients with MASLD who underwent carotid artery ultrasound were enrolled. Maximum intima-media thickness including plaques (Max-IMT) was measured by ultrasound. To predict liver fibrosis, liver stiffness was measured by vibration-controlled transient elastography and the fibrosis 4 (FIB-4) index was calculated. Coronary computed tomography angiography was performed to detect coronary artery stenosis based on a Max-IMT of ≥ 1.1 mm. RESULTS: The median Max-IMT was 1.3 mm, and 63 patients (41.2%) had a Max-IMT of ≥ 1.5 mm. FIB-4 index and liver stiffness was significantly correlated with Max-IMT, respectively (ρ=0.356, p＜0.001, ρ=0.25, p=0.002). Liver stiffness was significantly associated with a Max-IMT of ≥1.5 mm, independent of age. Individuals with higher FIB-4 index had moderate or severe coronary artery stenosis more frequently. Individuals with higher LSM level also had moderate or severe coronary artery stenosis more frequently, especially severe stenosis. CONCLUSIONS: Liver fibrosis parameters were associated with carotid artery atherosclerosis and coronary artery stenosis. Evaluation of liver fibrosis may be useful to identify significant atherosclerosis and coronary artery stenosis in patients with MASLD.

Structural basis for the recognition of the scaffold protein Frmpd4/Preso1 by the TPR domain of the adaptor protein LGN.

The adaptor protein LGN interacts via the N-terminal domain comprising eight tetratricopeptide-repeat (TPR) motifs with its partner proteins mInsc, NuMA, Frmpd1 and Frmpd4 in a mutually exclusive manner. Here, the crystal structure of the LGN TPR domain in complex with human Frmpd4 is described at 1.5 Å resolution. In the complex, the LGN-binding region of Frmpd4 (amino-acid residues 990-1011) adopts an extended structure that runs antiparallel to LGN along the concave surface of the superhelix formed by the TPR motifs. Comparison with the previously determined structures of the LGN-Frmpd1, LGN-mInsc and LGN-NuMA complexes reveals that these partner proteins interact with LGN TPR1-6 via a common core binding region with consensus sequence (E/Q)XEX4-5(E/D/Q)X1-2(K/R)X0-1(V/I). In contrast to Frmpd1, Frmpd4 makes additional contacts with LGN via regions N- and C-terminal to the core sequence. The N-terminal extension is replaced by a specific α-helix in mInsc, which drastically increases the direct contacts with LGN TPR7/8, consistent with the higher affinity of mInsc for LGN. A crystal structure of Frmpd4-bound LGN in an oxidized form is also reported, although oxidation does not appear to strongly affect the interaction with Frmpd4.

Induction of micronuclei in germinating onion seed root tip cells irradiated with high energy heavy ions.

Effects of high LET charged particles on a perfect in-vivo system are an essential theme for the study of the biological effects of radiation. Germinating onion seeds are independent complete organisms and the radiation induced micronuclei in the root chip cells can be examined quantitatively and theoretically. We irradiated with three types of high energy accelerated heavy ions germinating onion seeds using a synchrotron and observed micronuclei in the root tip cells. Micronuclei induction showed characteristic dose responses of an upward convex bell shape and a steep rise near zero doses for all types of the ions. The bell curve dose responses, however, could be explained by a simple mathematical model. A parameter in the model which indicates micronuclei induction frequency and another parameter which indicates induction frequency of lethal damages (or damages delaying cell divisions) per heavy ion track were both proportional to square of the LET. Because we suspected by-stander effect concerning the dose responses rising steeply near zero doses and tapering off for higher doses, we tested acute irradiation to remove time of information transmittance between cells using a single spill (about 0.3 s) of the synchrotron beam. No difference was detected between normal multiple spill irradiations and single spill.