Distinct stages in the recognition, sorting, and packaging of proTGFα into COPII-coated transport vesicles

CircUCK2(2,3) promotes cancer progression and enhances synergistic cytotoxicity of lenvatinib with EGFR inhibitors via activating CNIH4-TGFα-EGFR signaling

BACKGROUND

Circular (circ)RNAs have emerged as crucial contributors to cancer progression. Nonetheless, the expression regulation, biological functions, and underlying mechanisms of circRNAs in mediating hepatocellular carcinoma (HCC) progression remain insufficiently elucidated.

METHODS

We identified circUCK2(2,3) through circRNA sequencing, RT-PCR, and Sanger sequencing. CircUCK2(2,3) levels were measured in two independent HCC cohorts using quantitative real-time PCR (qRT-PCR). We explored the functions of circUCK2(2,3) using gain- and loss-of-function assays. Techniques such as RNA-sequencing, RNA immunoprecipitation (RIP), polysome fractionation, RNA pulldown, dual luciferase reporter assay, inhibitors of EGFR downstream signaling, CRISPR-Cas9, and medium transfer assays were employed to investigate the regulatory mechanisms and the protumoral activities of circUCK2(2,3). Additionally, in vitro cytotoxic assays and patient-derived xenograft (PDX) models assessed the effects of circUCK2(2,3) on the cytotoxic synergy of lenvatinib and EGFR inhibitors.

RESULTS

CircUCK2(2,3) is upregulated in HCC tissues and serves as an independent risk factor for poor recurrence-free survival. The expression of circUCK2(2,3) is independent on its host gene, UCK2, but is regulated by its upstream promoter and flanking inverted complementary sequences. Functionally, circUCK2(2,3) enhances HCC proliferation, migration, and invasion, both in vitro and in vivo. Mechanistically, by sponging miR-149-5p, circUCK2(2,3) increases CNIH4 levels, which in turn amplifies TGFα secretion, resulting in the activation of EGFR and downstream pAKT and pERK signaling pathways. Moreover, circUCK2(2,3) overexpression sensitizes HCC cells to EGFR inhibitors, and increases the synergistic cytotoxicity of combined lenvatinib and EGFR inhibitor treatment.

CONCLUSIONS

CircUCK2(2,3) regulates a novel oncogenic pathway, miR-149-5p-CNIH4-TGFα-EGFR, in HCC, presenting a viable therapeutic target and biomarker for the precision treatment of HCC.

Sex Differences in the Role of CNIH3 on Spatial Memory and Synaptic Plasticity

BACKGROUND

CNIH3 is an AMPA receptor (AMPAR) auxiliary protein prominently expressed in the dorsal hippocampus (dHPC), a region that plays a critical role in spatial memory and synaptic plasticity. However, the effects of CNIH3 on AMPAR-dependent synaptic function and behavior have not been investigated.

METHODS

We assessed a gain-of-function model of Cnih3 overexpression in the dHPC and generated and characterized a line of Cnih3-/- C57BL/6 mice. We assessed spatial memory through behavioral assays, protein levels of AMPAR subunits and synaptic proteins by immunoblotting, and long-term potentiation in electrophysiological recordings. We also utilized a super-resolution imaging workflow, SEQUIN (Synaptic Evaluation and Quantification by Imaging of Nanostructure), for analysis of nanoscale synaptic connectivity in the dHPC.

RESULTS

Overexpression of Cnih3 in the dHPC improved short-term spatial memory in female mice but not in male mice. Cnih3-/- female mice exhibited weakened short-term spatial memory, reduced dHPC synapse density, enhanced expression of calcium-impermeable AMPAR (GluA2-containing) subunits in synaptosomes, and attenuated long-term potentiation maintenance compared with Cnih3+/+ control mice; Cnih3-/- males were unaffected. Further investigation revealed that deficiencies in spatial memory and changes in AMPAR composition and synaptic plasticity were most pronounced during the metestrus phase of the estrous cycle in female Cnih3-/- mice.

CONCLUSIONS

This study identified a novel effect of sex and estrous on CNIH3's role in spatial memory and synaptic plasticity. Manipulation of CNIH3 unmasked sexually dimorphic effects on spatial memory, synaptic function, AMPAR composition, and hippocampal plasticity. These findings reinforce the importance of considering sex as a biological variable in studies of memory and hippocampal synaptic function.

A CLN6-CLN8 complex recruits lysosomal enzymes at the ER for Golgi transfer

Lysosomal enzymes are synthesized in the endoplasmic reticulum (ER) and transferred to the Golgi complex by interaction with the Batten disease protein CLN8 (ceroid lipofuscinosis, neuronal, 8). Here we investigated the relationship of this pathway with CLN6, an ER-associated protein of unknown function that is defective in a different Batten disease subtype. Experiments focused on protein interaction and trafficking identified CLN6 as an obligate component of a CLN6-CLN8 complex (herein referred to as EGRESS: ER-to-Golgi relaying of enzymes of the lysosomal system), which recruits lysosomal enzymes at the ER to promote their Golgi transfer. Mutagenesis experiments showed that the second luminal loop of CLN6 is required for the interaction of CLN6 with the enzymes but dispensable for interaction with CLN8. In vitro and in vivo studies showed that CLN6 deficiency results in inefficient ER export of lysosomal enzymes and diminished levels of the enzymes at the lysosome. Mice lacking both CLN6 and CLN8 did not display aggravated pathology compared with the single deficiencies, indicating that the EGRESS complex works as a functional unit. These results identify CLN6 and the EGRESS complex as key players in lysosome biogenesis and shed light on the molecular etiology of Batten disease caused by defects in CLN6.

Classification of Trispanins: A Diverse Group of Proteins That Function in Membrane Synthesis and Transport Mechanisms

As the structure and functions of proteins are correlated, investigating groups of proteins with the same gross structure may provide important insights about their functional roles. Trispanins, proteins that contain three alpha-helical transmembrane (3TM) regions, have not been previously studied considering their transmembrane features. Our comprehensive identification and classification using bioinformatic methods describe 152 3TM proteins. These proteins are frequently involved in membrane biosynthesis and lipid biogenesis, protein trafficking, catabolic processes, and in particular signal transduction due to the large ionotropic glutamate receptor family. Proteins that localize to intracellular compartments are overrepresented in the dataset in comparison to the entire human transmembrane proteome, and nearly 45% localize specifically to the endoplasmic reticulum (ER). Furthermore, nearly 20% of the trispanins function in lipid metabolic processes and transport, which are also overrepresented. Nearly one-third of trispanins are identified as being targeted by drugs and/or being associated with diseases. A high number of 3TMs have unknown functions and based on this analysis we speculate on the functional involvement of uncharacterized trispanins in relationship to disease or important cellular activities. This first overall study of trispanins provides a unique analysis of a diverse group of membrane proteins.

The protein secretion modulator TMED9 drives CNIH4/TGFα/GLI signaling opposing TMED3-WNT-TCF to promote colon cancer metastases

How cells in primary tumors initially become pro-metastatic is not understood. A previous genome-wide RNAi screen uncovered colon cancer metastatic suppressor and WNT promoting functions of TMED3, a member of the p24 ER-to-Golgi protein secretion family. Repression of canonical WNT signaling upon knockdown (kd) of TMED3 might thus be sufficient to drive metastases. However, searching for transcriptional influences on other family members here we find that TMED3 kd leads to enhanced TMED9, that TMED9 acts downstream of TMED3 and that TMED9 kd compromises metastasis. Importantly, TMED9 pro-metastatic function is linked to but distinct from the repression of TMED3-WNT-TCF signaling. Functional rescue of the migratory deficiency of TMED9 kd cells identifies TGFα as a mediator of TMED9 pro-metastatic activity. Moreover, TMED9 kd compromises the biogenesis, and thus function, of TGFα. Analyses in three colon cancer cell types highlight a TMED9-dependent gene set that includes CNIH4, a member of the CORNICHON family of TGFα exporters. Our data indicate that TGFA and CNIH4, which display predictive value for disease-free survival, promote colon cancer cell metastatic behavior, and suggest that TMED9 pro-metastatic function involves the modulation of the secretion of TGFα ligand. Finally, TMED9/TMED3 antagonism impacts WNT-TCF and GLI signaling, where TMED9 primacy over TMED3 leads to the establishment of a positive feedback loop together with CNIH4, TGFα, and GLI1 that enhances metastases. We propose that primary colon cancer cells can transition between two states characterized by secretion-transcription regulatory loops gated by TMED3 and TMED9 that modulate their metastatic proclivities.

Traffic from the endosome towards trans-Golgi network

Retrograde passage of a transport carrier entails cargo sorting at the endosome, generation of a cargo-laden carrier and its movement along cytoskeletal tracks towards trans-Golgi network (TGN), tethering at the TGN, and fusion with the Golgi membrane. Significant advances have been made in understanding this traffic system, revealing molecular requirements in each step and the functional connection between them as well as biomedical implication of the dysregulation of those important traffic factors. This review focuses on describing up-to-date action mechanisms for retrograde transport from the endosomal system to the TGN.

EGF receptor ligands: recent advances

Seven ligands bind to and activate the mammalian epidermal growth factor (EGF) receptor (EGFR/ERBB1/HER1): EGF, transforming growth factor-alpha (TGFA), heparin-binding EGF-like growth factor (HBEGF), betacellulin (BTC), amphiregulin (AREG), epiregulin (EREG), and epigen (EPGN). Of these, EGF, TGFA, HBEGF, and BTC are thought to be high-affinity ligands, whereas AREG, EREG, and EPGN constitute low-affinity ligands. This focused review is meant to highlight recent studies related to actions of the individual EGFR ligands, the interesting biology that has been uncovered, and relevant advances related to ligand interactions with the EGFR.