Molecular and Cellular Biology最新文献

Rho GTPases are Ras-like proteins that contribute to many aspects of human cancer. However, unlike Ras, Rho proteins are not often mutagenically activated in cancers, but require activation by upstream proteins known as Rho GDP exchange factors (RhoGEFs). The neuroepithelial transforming gene 1 (Net1) is a RhoA/RhoB-specific GEF that is overexpressed in many cancers, and high levels of Net1 protein expression often correlate with reduced disease-free and overall survival. Net1 promotes multiple phenotypes in cancer cells, including cell motility, invasion, and proliferation. It does so by regulating diverse signaling pathways that ultimately control actin cytoskeletal organization, transcription, DNA damage signaling, and mitosis. In tumors, Net1 is required for tumor cell proliferation, tumor angiogenesis, and distant metastasis. In this review we will delineate the evidence supporting a role for Net1 in tumor progression, and describe mechanisms that regulate Net1 expression and cellular activity.

The PAQosome (R2TP/PFDL complex) is a recently characterized co-chaperone of Hsp90 that orchestrates the assembly and stabilization of diverse macromolecular protein complexes essential for cellular homeostasis. It consists of RUVBL1, RUVBL2, PIH1D1, RPAP3 and a PFDL module consisting of prefoldin and prefoldin-like proteins. RPAP3 and PIH1D1 are subunits exclusively for the R2TP complex, and they act as central adaptors through their interactions with RUVBL1/2, Hsp90 and clients. Originally described in the context of ribonucleoprotein and PIKK assembly, evolving evidence now implicates PIH1D1 and RPAP3 in a broad spectrum of biological processes, including ciliogenesis, RNA silencing, DNA damage response, metabolic regulation, and oncogenesis. The mechanistic basis of substrate recognition, the phosphorylation-independent interactions, and the functional contribution of alternative PAQosome assemblies remain limited. This review highlights PIH1D1 and RPAP3 as dynamic proteins at the crossroads of protein homeostasis, signaling pathways, and diseases.

To maintain genome stability, proliferating cells must enact a program of telomere maintenance. While most tumors maintain telomeres using telomerase, a subset of tumors utilize a DNA-templated process termed alternative lengthening of telomeres or ALT. ALT is associated with mutations in the ATRX/DAXX/H3.3 histone chaperone complex, which is responsible for deposition of histone variant H3.3 at heterochromatic regions of the genome including telomeres. We wished to better understand the role DAXX plays in ALT suppression, and to determine which disease-associated DAXX mutations are unable to suppress ALT. To answer this question, we leveraged the G292 cell line, in which ATRX is wild-type but DAXX has undergone a fusion event. Restoration of wild-type DAXX in G292 localizes ATRX and abrogates ALT. Using this model system, we tested the ability of disease-associated DAXX missense variants to suppress ALT. Missense mutations in the ATRX binding domain, the histone binding domain, and the C-terminal SUMO interaction motif reduce the ability of DAXX to suppress ALT. Unexpectedly, we find that mutations in the DAXX histone binding domain lead to failure of ATRX localization. We conclude that a key function of DAXX in ALT suppression is the localization of ATRX to nuclear foci.

Inflammation and ferroptosis play a crucial role in cisplatin (CP)-induced acute kidney injury (AKI). Silybin (SYB), a polyphenolic flavonoid, has shown renal protective effects, but its underlying mechanisms remain unclear. CP-induced HK-2 cell and mouse AKI models were used to explore the role of SYB. CCK-8, lactate dehydrogenase release, flow cytometry, and calcein/PI staining, were performed to evaluate cell viability, proliferation, and apoptosis. Oxidative stress and ferroptosis markers were measured, while renal function was assessed by serum creatinine and urea nitrogen. Mitochondrial ultrastructure was examined, and histological staining was conducted to analyze renal pathology and iron deposition. Western blotting detected HDAC6, NF-κB, NLRP3, and ferroptosis-related proteins expression. SYB treatment alleviated CP-induced mitochondrial damage, reduced lactate dehydrogenase release, inflammatory cytokines, oxidative stress, and ferroptosis, and improved proliferation and viability in HK-2 cells. In mice, 100 mg/kg SYB decreased serum creatinine, urea nitrogen, and cytokine levels, while ameliorating renal tissue injury. Mechanistically, SYB downregulated HDAC6 and inhibited NF-κB/NLRP3 activation, thereby suppressing ferroptosis. Notably, overexpression of HDAC6 restored NF-κB/NLRP3 activity and attenuated the protective effects of SYB. In conclusion, SYB mitigates CP-induced AKI by reducing inflammation and ferroptosis by modulating the HDAC6/NF-κB/NLRP3 pathway.

Ulcerative colitis (UC) is a clinically common idiopathic inflammatory bowel disease. The DSS-induced colitis model was induced via 5% DSS for 7 days. Rats were gavaged with QLJCN solution in different concentrations. This study measured body weight, colon length, and DAI of rats in each group. The hematoxylin-eosin staining assessed the histopathology and histological score. Western blot analysis examined the expressions of TFF3, MUC-2, JAK2/STAT3 pathway-, and TLR4/NF-κB pathway-related markers. Moreover, the contents of IL-6, TNF-α, and LPS in the colons/serum were determined by ELISA. TLR4 activator (RS09) or JAK2/STAT3 activator (colivelin) were employed for the rescue experiments. QLJCN repressed weight loss and the increase of DAI score in DSS rats. QLJCN also increased the colon length and alleviated colonic damage, and effectively repressed the levels of IL-6 and TNF-α but elevated the levels of TFF3 and MUC-2 in the colons/serum of DSS rats. Moreover, QLJCN weakened the activation of JAK2/STAT3 and TLR4/NF-κB pathways, and alleviated the intestinal inflammation. Furthermore, these ameliorative effects of QLJCN were reversed by TLR4 activator (RS09) or JAK2/STAT3 activator (colivelin). QLJCN has protective effects on DSS-induced colitis rats by restraining JAK2/STAT3 and TLR4/NF-κB pathways. This study provides new therapeutic strategies for UC.

Since its discovery several decades ago, the proteasome has been recognized as one of the most complex and highly evolved proteolytic systems. Through the selective and rapid degradation of ubiquitinated proteins, it plays a pivotal role in maintaining cellular proteostasis and governing essential biological processes such as cell cycle regulation and signal transduction. Recent advances in cryo-electron microscopy (cryo-EM), together with developments in mass spectrometry and large-scale genetic screening, have provided unprecedented insights into proteasome biology. These approaches have not only revealed the proteasome as a precisely engineered molecular machine optimized for substrate specificity and efficient degradation, but have also facilitated the identification of previously unrecognized regulatory factors and post-translational modifications that fine-tune its activity. Moreover, accumulating evidence has demonstrated that proteasome capacity is tightly regulated at multiple levels, including transcriptional control, assembly dynamics, and subcellular localization, to meet diverse cellular demands and preserve proteostasis. Importantly, dysregulation of these processes is linked to human diseases, underscoring the proteasome's central role in cellular physiology and its promise as a therapeutic target. Ongoing research is uncovering new regulatory layers and structural complexities, highlighting the proteasome's indispensable and versatile role in health and disease.

Cholesterol trafficking from the endoplasmic reticulum (ER) through the mitochondria-associated ER membrane (MAM) and finally to mitochondria is essential for mammalian survival. ER lipid raft-associated protein 2 (ERLIN2) scaffolds raft-like microdomains in the trans-Golgi network, endosomes, and plasma membrane. We found that ERLIN2 assists in rolling cholesterol trafficking-associated lipid vesicles by facilitating the intermediate folding of cholesterol trafficker steroidogenic acute regulatory protein (StAR) from the ER to MAM prior to delivery to the outer mitochondrial membrane. Each ERLIN2-StAR interaction is short. The absence of ERLIN2 ablates mitochondrial cholesterol transport. Over time, StAR association with ERLIN2 increases from the ER to MAM, thereby enhancing mitochondrial cholesterol transport. Thus, ERLIN2 is central for regulating mitochondrial cholesterol trafficking required for mitochondrial steroid metabolism.

Pyridinyl-imidazole class p38 MAPKα/β (MAPK14/MAPK11) inhibitors including SB202190 have been shown to induce cell-type specific defective autophagy resulting in micron-scale vacuole formation, cell death, and tumor suppression. We had earlier shown that this is an off-target effect of SB202190. Here we provide evidence that this vacuole formation is independent of ATG5-mediated canonical autophagosome initiation. While SB202190 interferes with autophagic flux in many cell lines parallel to vacuolation, autophagy-deficient DU-145 cells and CRISPR/Cas9 gene-edited ATG5-knockout A549 cells also undergo vacuolation upon SB202190 treatment. Late-endosomal GTPase RAB7 colocalizes with these compartments and RAB7 GTP-binding is essential for SB202190-induced vacuolation. A screen for modulators of SB202190-induced vacuolation revealed molecules including multi-kinase inhibitor sorafenib as inhibitors of vacuolation and sorafenib co-treatment enhanced cytotoxicity of SB202190. Moreover, VE-821, an ATR inhibitor was found to phenocopy the cell-type specific vacuolation response of SB202190. To identify the factors determining the cell-type specificity of vacuolation induced by SB-compounds and VE-821, we compared the transcriptomics data from vacuole-forming and non-vacuole-forming cancer cell lines and identified a gene expression signature that may define sensitivity of cells to these small-molecules. Further analyses using small molecule tools and the gene signature discovered here, could reveal novel mechanisms regulating this interesting anti-cancer phenotype.