Miho Iijima

E-cadherin suppresses invasion and promotes metastasis in invasive ductal breast cancer, through suppression of reactive oxygen species (ROS). We sought to determine the cellular source of apoptosis-inducing ROS and to identify the domains of E-cadherin that are essential for cancer cell survival. Inhibition of mitochondria-derived ROS was sufficient to rescue cell death following E-cadherin deletion, in both 3D colony formation and in vivo metastasis assays. We next generated Cdh1 constructs by mutating amino acids or deleting domains, then tested their ability to rescue colony formation in E-cadherin–deleted cells. Surprisingly, E-cadherin constructs in which the extracellular domains were deleted, adhesion was compromised, or catenin interactions were blocked could rescue elevated mitochondrial ROS and 3D colony formation. Conversely, a construct lacking the cytoplasmic domain was unable to rescue ROS or cell death. Our findings reveal that E-cadherin’s ability to regulate mitochondrial ROS, cancer cell survival, and metastatic outgrowth is separable from its role in intercellular adhesion.

The morphology of the endoplasmic reticulum (ER), characterized by central sheets and peripheral tubules, is controlled by membrane-shaping proteins. However, the role of lipids in ER morphogenesis remains elusive, despite the ER being the major site for lipid synthesis. Here, by examining the role of eighteen phosphatidic acid (PA)-generating enzymes in ER morphology, we identify lysophosphatidic acid acyltransferase 2 (AGPAT2) as a critical factor in mouse and human cells. AGPAT2 produces PA in the glycerophospholipid/triacylglycerol biosynthesis pathway, and its mutations cause congenital generalized lipodystrophy. We find that AGPAT2-generated PA drives ER tubulation through gene knockout, 3D structural analysis by FIB-SEM, super-resolution microscopy, lipidomics, AlphaFold, and in vitro reconstitutions of ER tubulation and AGPAT2 activity. AGPAT2 interacts with and supplies PA to the PA-binding, dynamin-related GTPase, DRP1, which subsequently tubulates the ER in a manner independent of GTP hydrolysis and oligomerization, distinct from its function in mitochondrial division. Consistently, the reduction of PA levels by ectopic expression of a PA phosphatase, LIPIN1, transforms ER tubules into sheets. Our results reveal an unforeseen interplay between lipid biosynthesis and membrane organization in the ER.

Mitochondrial division and fusion are critical regulators of cancer cell metabolism, proliferation, survival, metastasis, and drug resistance. Division promotes tumor development by reprogramming energy metabolism, whereas its inhibition can suppress tumor growth and metastasis. The mechanochemical GTPase DRP1, a key mediator of mitochondrial division, has emerged as a promising therapeutic target. Mitochondrial cristae also contribute to cancer progression by modulating metabolic reprogramming and oncogenic signaling. Targeting these processes may stimulate anti-tumor innate immune responses through the release of mitochondrial DNA into the cytoplasm. A deeper understanding of tumor-specific mitochondrial membrane structures and dynamics could therefore reveal novel intervention strategies and guide precision cancer therapies.

Mitochondrial stress pathways protect mitochondrial health from cellular insults^{1,2,3,4,5,6,7,8}. However, their role under physiological conditions is largely unknown. Here, using 18 single, double and triple whole-body and tissue-specific knockout and mutant mice, along with systematic mitochondrial morphology analysis, untargeted metabolomics and RNA sequencing, we discovered that the synergy between two stress-responsive systems—the ubiquitin E3 ligase Parkin and the metalloprotease OMA1—safeguards mitochondrial structure and genome by mitochondrial fusion, mediated by the outer membrane GTPase MFN1 and the inner membrane GTPase OPA1. Whereas the individual loss of Parkin or OMA1 does not affect mitochondrial integrity, their combined loss results in small body size, low locomotor activity, premature death, mitochondrial abnormalities and innate immune responses. Thus, our data show that Parkin and OMA1 maintain a dual regulatory mechanism that controls mitochondrial fusion at the two membranes, even in the absence of extrinsic stress.

Epidermal growth factor receptor (EGFR) is a major oncogenic protein, and thus EGFR-targeting therapies are widely used in patients with various types of cancer, including lung cancer. However, resistance to EGFR inhibitors, such as erlotinib, presents a significant challenge in treating lung cancer. In this study, we established an EGFR-independent, erlotinib-resistant (ER) phenotype in lung cancer A549 cells by exposing them to erlotinib for an extended period. The resulting ER cells exhibited a dramatic increase in erlotinib resistance, a decreased EGFR protein level, and enhanced tumor growth, suggesting a robust mechanism bypassing EGFR inhibition. RNA sequencing identified the transcription factor GRHL2 as a critical player in this resistance. GRHL2 was upregulated in ER cells, and its knockdown and knockout significantly reduced erlotinib resistance. Further analysis revealed that GRHL2 upregulates the receptor tyrosine kinase HER3, and that HER3 knockdown similarly decreases the IC₅₀ for erlotinib. Additionally, ER cells showed increased cell-cell adhesion, linked to upregulated E-cadherin. E-cadherin was found to be vital for erlotinib resistance, largely independent of GRHL2, highlighting multiple parallel pathways sustaining resistance. These findings provide a novel mechanism of drug resistance and suggest that combination therapies targeting both GRHL2-HER3 and E-cadherin-mediated pathways may be necessary to overcome erlotinib resistance in lung cancer.