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Previously, we reported that non‐apoptotic cell death was induced in non‐malignant mammary epithelial cells (HMECs) upon loss of anchorage during 48 h incubation in suspension. In this study, we examined HMECs in suspension at an earlier time point and found that most of them lost attachment ability to substrata when replated, although >80% were alive. This suggested that HMECs lost reattachment ability (RA) prior to cell death upon detachment. Concomitant with the loss of RA, a decrease in the levels of β1 and β4 integrin was observed. In sharp contrast, breast cancer cells retained integrin levels, reattached to substrata, and formed colonies after exposure to anchorage loss as efficiently as those maintained under adherent conditions. Such RA of cancer cells is essential for the metastatic process, especially for establishing adhesion contact with ECM in the secondary organ after systemic circulation. Further analysis suggested that sustained levels of β4 integrin, which was mediated by Rac1, was critical for RA after anchorage loss and lung metastasis of breast cancer cells. In the cancer cells, persistent Rac1 activity enhanced escape of β4 integrin from lysosomal degradation depending on actin‐related protein 2/3 and TBC1D2, a GTPase‐activating protein of Rab7 GTPase. Notably, simultaneous high expression of ITGB4 and RAC1 was associated with poor prognosis in patients with breast cancer. Therefore, β4 integrin and Rac1 are attractive therapeutic targets to eliminate RA in cancer cells, thereby preventing the initial step of colonization at the secondary organ during metastasis. Anchorage‐independent reattachment ability (RA) of cells is as important as anchorage‐independent survival or growth for cancer metastasis. The Rac1/beta4 integrin axis has emerged as a critical mediator of RA of breast cancer cells in this study. Notably, simultaneous high expression of RAC1 and ITGB4 was associated with poor prognosis in patients with breast cancer.

The adenylation (A) domain is essential for non-ribosomal peptide synthetases (NRPSs), which synthesize various peptide-based natural products, including virulence factors, such as siderophores and genotoxins. Hence, the inhibition of A-domains could attenuate the virulence of pathogens. 5’- O - N -(Aminoacyl or arylacyl)sulfamoyladenosine (AA-AMS) is a bisubstrate small-molecule inhibitor of the A-domains of NRPSs. However, the bacterial cell permeability of AA-AMS is typically a problem owing to its high hydrophilicity. In this study, we investigated the influence of a modification of 2′-OH in the AMS scaffold with different functional groups on binding to target enzymes and bacterial cell penetration. The inhibitor 7 with a cyanomethyl group at 2′-OH showed desirable inhibitory activity against both recombinant and intracellular gramicidin S synthetase A (GrsA) in the gramicidin S-producer Aneurinibacillus migulanus ATCC 9999, providing an alternative scaffold to develop novel A-domain inhibitors.

Recent comprehensive analyses of mtDNA and orthogonal RNA‐sequencing data revealed that in numerous human cancers, mtDNA copy numbers and mtRNA amounts are significantly reduced, followed by low respiratory gene expression. Under such conditions (called mt‐Low), cells encounter severe cell proliferation defects; therefore, they must acquire countermeasures against this fatal disadvantage during malignant transformation. This study elucidated a countermeasure against the mt‐Low condition‐induced antiproliferative effects in hepatocellular carcinoma (HCC) cells. The mechanism relied on the architectural transcriptional regulator HMGA2, which was preferably expressed in HCC cells of the mt‐Low type in vitro and in vivo. Detailed in vitro analyses suggest that HMGA2 regulates insulin‐like growth factor binding protein 1 (IGFBP1) expression, leading to AKT activation, which then phosphorylates the cyclin‐dependent kinase inhibitor (CKI), P27KIP1, and facilitates its ubiquitin‐mediated degradation. Accordingly, intervention in the HMGA2 function by RNAi resulted in an increase in P27KIP1 levels and an induction of senescence‐like cell proliferation inhibition in mt‐Low‐type HCC cells. Conclusively, the HMGA2/IGFBP1/AKT axis has emerged as a countermeasure against P27KIP1 CKI upregulation under mt‐Low conditions, thereby circumventing cell proliferation inhibition and supporting the tumorigenic state. Notably, similar to in vitro cell lines, HMGA2 was likely to regulate IGFBP1 expression in HCC in vivo, thereby contributing to poor patient prognosis. Considering the significant number of cases under mt‐Low or the threat of CKI upregulation cancer‐wide, the axis is noteworthy as a vulnerability of cancer cells or target for tumor‐agnostic therapy inducing irreversible cell proliferation inhibition via CKI upregulation in a large population with cancer. mtDNA copy numbers and mtRNA amounts are reduced, followed by low respiratory gene expression in numerous cancer cells. High expression of HMGA2 activates the IGFBP1/AKT pathway, circumventing mitochondria deficiency‐caused cell proliferation defects. Intervention in the HMGA2 function results in an increase in P27KIP protein levels and an induction of senescence‐like cell cycle arrest in cancer cells.

The role of the electron transport chain (ETC) in cell proliferation control beyond its crucial function in supporting ATP generation has recently emerged. In this study, we found that, among the four ETC complexes, the complex I (CI)‐mediated NAD+ regeneration is important for cancer cell proliferation. In cancer cells, a decrease in CI activity by RNA interference (RNAi) against NADH:ubiquinone oxidoreductase core subunit V1 (NDUFV1) arrested the cell cycle at the G1/S phase, accompanying upregulation of p21Cip1 cyclin‐dependent kinase inhibitor expression. Mechanistically, a decrease in the NAD+/NADH ratio downregulated SIRT3 and SIRT7 function, which suppressed p21Cip1 expression at the translational and transcriptional levels, respectively, resulting in the upregulation of the antiproliferative molecule. Importantly, high expression levels of the core subunits of CI correlated with poor prognosis in patients with the hormone receptor(+)/human epidermal growth factor receptor 2(−) (HR+/HER2−) subtype of breast cancer. Therefore, NDUFV1 and SIRT3/7 have emerged as promising therapeutic targets against this breast cancer subtype. NAD+ regeneration by mitochondrial complex I NADH dehydrogenase is important for cancer cell proliferation. Specifically, NAD+ is necessary for the activities of NAD+‐dependent deacetylases SIRT3 and SIRT7, which suppress the expression of p21Cip1 cyclin‐dependent kinase inhibitor, an antiproliferative molecule, at the translational and transcriptional levels, respectively. Thus, the NAD+–SIRT3/7–p21Cip1 pathway couples cellular metabolism and proliferation, supporting cancer cell proliferation.

A highly specific chemical crosslinking method is used to trap a complex between an acyl carrier protein and a fatty acid dehydratase during fatty acid biosynthesis; subsequent X-ray crystallography, NMR spectroscopy and molecular dynamics simulations techniques enable the detailed study of this complex. Acyl carrier protein structures revealed During fatty acid and polyketide biosynthesis the growing polymer chain is stabilized by acyl carrier proteins (ACPs), but the transient nature of the process makes it difficult to visualize the molecular mechanisms involved. Two papers published in this issue of Nature use strategies that circumvent this problem. Ali Masoudi et al . solve the X-ray crystal structures of an ACP from Escherichia coli bound to LpxD, an acyltransferase in the lipid A biosynthetic pathway, in three different states: an intact acyl-ACP, a hydrolysed-acyl-ACP, and a holo-ACP form. Alignment of these structures makes it possible to visualize the conformational changes that take place in the ACP during catalysis. Chi Nguyen et al . use a crosslinking probe to tether an ACP to an active site histidine of one of its catalytic enzymes, the dehydratase FabA from E. coli . They obtain a high-resolution X-ray crystal structure of the stabilized ACP–FabA complex and use NMR spectroscopy to probe the dynamics of ACP–FabA interactions. Their experiments support a 'switchblade' model. This crosslink-probe approach can be applied to other carrier protein partners in metabolic and signalling pathways. Acyl carrier protein (ACP) transports the growing fatty acid chain between enzymatic domains of fatty acid synthase (FAS) during biosynthesis 1 . Because FAS enzymes operate on ACP-bound acyl groups, ACP must stabilize and transport the growing lipid chain 2 . ACPs have a central role in transporting starting materials and intermediates throughout the fatty acid biosynthetic pathway 3 , 4 , 5 . The transient nature of ACP–enzyme interactions impose major obstacles to obtaining high-resolution structural information about fatty acid biosynthesis, and a new strategy is required to study protein–protein interactions effectively. Here we describe the application of a mechanism-based probe that allows active site-selective covalent crosslinking of AcpP to FabA, the Escherichia coli ACP and fatty acid 3-hydroxyacyl-ACP dehydratase, respectively. We report the 1.9 Å crystal structure of the crosslinked AcpP–FabA complex as a homodimer in which AcpP exhibits two different conformations, representing probable snapshots of ACP in action: the 4′-phosphopantetheine group of AcpP first binds an arginine-rich groove of FabA, then an AcpP helical conformational change locks AcpP and FabA in place. Residues at the interface of AcpP and FabA are identified and validated by solution nuclear magnetic resonance techniques, including chemical shift perturbations and residual dipolar coupling measurements. These not only support our interpretation of the crystal structures but also provide an animated view of ACP in action during fatty acid dehydration. These techniques, in combination with molecular dynamics simulations, show for the first time that FabA extrudes the sequestered acyl chain from the ACP binding pocket before dehydration by repositioning helix III. Extensive sequence conservation among carrier proteins suggests that the mechanistic insights gleaned from our studies may be broadly applicable to fatty acid, polyketide and non-ribosomal biosynthesis. Here the foundation is laid for defining the dynamic action of carrier-protein activity in primary and secondary metabolism, providing insight into pathways that can have major roles in the treatment of cancer, obesity and infectious disease.

Obstructive sleep apnea syndrome (OSAS) is characterized by cycles of decreased blood oxygen saturation followed by reoxygenation due to transient apnea. Cognitive dysfunction is a complication of OSAS, but its mechanisms remain unclear. Eight-week-old C57BL/6J mice were exposed to intermittent hypoxia (IH) to model OSAS, and cognitive function and hippocampal gene expression were analyzed. Three groups were maintained for 28 days: an IH group (oxygen alternating between 10 and 21% in 2 min cycles, 8 h/day), sustained hypoxia group (SH) (10% oxygen, 8 h/day), and control group (21% oxygen). Behavioral tests and RNA sequencing (RNA-seq) analysis were performed. While Y-maze test results showed no differences, the IH group demonstrated impaired memory and learning in passive avoidance tests compared to control and SH groups. RNA-seq revealed coordinated suppression of mitochondrial function genes and oxidative stress response pathways, specifically in the IH group. RT-qPCR showed decreased Lars2, Hmcn1, and Vstm2l expression in the IH group. Pathway analysis showed the suppression of the KEAP1-NFE2L2 antioxidant pathway in the IH group vs. the SH group. Our findings demonstrate that IH induces cognitive dysfunction through suppression of the KEAP1-NFE2L2 antioxidant pathway and downregulation of mitochondrial genes (Lars2, Vstm2l), leading to oxidative stress and mitochondrial dysfunction. These findings advance our understanding of the molecular basis underlying OSAS-related cognitive impairment.

Homeostasis is achieved by balancing cell survival and death. In cancer cells, especially those carrying driver mutations, the processes and signals that promote apoptosis are inhibited, facilitating the survival and proliferation of these dysregulated cells. Apoptosis induction is an important mechanism underlying the therapeutic efficacy of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) for EGFR-mutated non-small cell lung cancer (NSCLC). However, the mechanisms by which EGFR-TKIs induce apoptosis have not been fully elucidated. A deeper understanding of the apoptotic pathways induced by EGFR-TKIs is essential for the developing novel strategies to overcome resistance to EGFR-TKIs or to enhance the initial efficacy through therapeutic synergistic combinations. Recently, therapeutic strategies targeting apoptosis have been developed for cancer. Here, we review the state of knowledge on EGFR-TKI-induced apoptotic pathways and discuss the therapeutic strategies for enhancing EGFR-TKI efficiency. We highlight the great progress achieved with third-generation EGFR-TKIs. In particular, combination therapies of EGFR-TKIs with anti-vascular endothelial growth factor/receptor inhibitors or chemotherapy have emerged as promising therapeutic strategies for patients with EGFR-mutated NSCLC. Nevertheless, further breakthroughs are needed to yield an appropriate standard care for patients with EGFR-mutated NSCLC, which requires gaining a deeper understanding of cancer cell dynamics in response to EGFR-TKIs.

Mitochondria are multifunctional organelles; they have been implicated in various aspects of tumorigenesis. In this study, we investigated a novel role of the basal electron transport chain (ETC) activity in cell proliferation by inhibiting mitochondrial replication and transcription (mtR/T) using pharmacological and genetic interventions, which depleted mitochondrial DNA/RNA, thereby inducing ETC deficiency. Interestingly, mtR/T inhibition did not decrease ATP levels despite deficiency in ETC activity in different cell types, including MDA‐MB‐231 breast cancer cells, but it severely impeded cell cycle progression, specifically progression during G2 and/or M phases in the cancer cells. Under these conditions, the expression of a group of cell cycle regulators was downregulated without affecting the growth signaling pathway. Further analysis suggested that the transcriptional network organized by E2F1 was significantly affected because of the downregulation of E2F1 in response to ETC deficiency, which eventually resulted in the suppression of cell proliferation. Thus, in this study, the E2F1‐mediated ETC‐dependent mechanism has emerged as the regulatory mechanism of cell cycle progression. In addition to E2F1, FOXM1 and BMYB were also downregulated, which contributed specifically to the defects in G2 and/or M phase progression. Thus, ETC‐deficient cancer cells lost their growing ability, including their tumorigenic potential in vivo. ETC deficiency abolished the production of reactive oxygen species (ROS) from the mitochondria and a mitochondria‐targeted antioxidant mimicked the deficiency, thereby suggesting that ETC activity signaled through ROS production. In conclusion, this novel coupling between ETC activity and cell cycle progression may be an important mechanism for coordinating cell proliferation and metabolism. A novel coupling between ETC activity and the core regulatory machinery for cell cycle progression.

Osimertinib, a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI), is used as a first-line treatment for patients with EGFR-mutant non-small cell lung cancer (NSCLC). However, the mechanisms underlying its anticancer activity, particularly the subsequent development of acquired resistance, are unclear. Herein, we investigated the mechanisms underlying the development of osimertinib resistance by treating NSCLC PC-9 cells (harboring an EGFR-activating mutation) with osimertinib, thereby developing five resistant cell lines, i.e., AZDR3, AZDR6, AZDR9, AZDR11, and AZDR14. The amplification of wild-type EGFR in AZDR3 cells and wild-type EGFR and KRAS in AZDR6 cells was also studied. AZDR3 cells showed dependence on EGFR signaling, in addition to afatinib sensitivity. AZDR9 cells harboring KRASG13D showed sensitivity to MEK inhibitors. Furthermore, combination treatment with EGFR and IGF1R inhibitors resulted in attenuated cell proliferation and enhanced apoptosis. In AZDR11 cells, increased Bim expression could not induce apoptosis, but Bid cleavage was found to be essential for the same. A SHP2/T507K mutation was also identified in AZDR14 cells, and, when associated with GAB1, SHP2 could activate ERK1/2, whereas a SHP2 inhibitor, TNO155, disrupted this association, thereby inhibiting GAB1 activation. Thus, diverse osimertinib resistance mechanisms were identified, providing insights for developing novel therapeutic strategies for NSCLC.

In most human cancers, somatic mutations have been identified in the mtDNA; however, their significance remains unclear. We recently discovered that NMuMG mouse mammary epithelial cells, when deprived of mitochondria or following inhibition of respiratory activity, undergo epithelial morphological disruption accompanied with irregular edging of E‐cadherin, the appearance of actin stress fibers, and an altered gene expression profile. In this study, using the mtDNA‐less pseudo ρ0 cells obtained from NMuMG mouse mammary epithelial cells, we examined the roles of two mitochondrial stress‐associated transcription factors, cAMP‐responsive element‐binding protein (CREB) and C/EBP homologous protein‐10 (CHOP), in the disorganization of epithelial phenotypes. We found that the expression of matrix metalloproteinase‐13 and that of GADD45A, SNAIL and integrin α1 in the ρ0 cells were regulated by CHOP and CREB, respectively. Of note, knockdown and pharmacological inhibition of CREB ameliorated the disrupted epithelial morphology. It is interesting to note that the expression of high mobility group AT‐hook 2 (HMGA2), a non‐histone chromatin protein implicated in malignant neoplasms, was increased at the protein level through the CREB pathway. Here, we reveal how the activation of the CREB/HMGA2 pathway is implicated in the repression of integrin α1 expression in HepG2 human cancer cells, highlighting the importance of the CREB/HMGA2 pathway in malignant transformation associated with mitochondrial dysfunction, thereby raising the possibility that the pathway indirectly interferes with the cell–cell adhesion structure by influencing the cell–extracellular matrix adhesion status. Overall, the data suggest that mitochondrial dysfunction potentially contributes to neoplastic transformation of epithelial cells through the activation of these transcriptional pathways.