Translocation of conventional protein kinases C (PKCs) to the plasma membrane leads to their specific association with transmembrane-4 superfamily (TM4SF; tetraspanin) proteins (CD9, CD53, CD81, CD82, and CD151), as demonstrated by reciprocal co-immunoprecipitation and covalent cross-linking experiments. Although formation and maintenance of TM4SF-PKC complexes are not dependent on integrins, TM4SF proteins can act as linker molecules, recruiting PKC into proximity with specific integrins. Previous studies showed that the extracellular large loop of TM4SF proteins determines integrin associations. In contrast, specificity for PKC association probably resides within cytoplasmic tails or the first two transmembrane domains of TM4SF proteins, as seen from studies with chimeric CD9 molecules. Consistent with a TM4SF linker function, only those integrins (␣ 3 ␤ 1 , ␣ 6 ␤ 1 , and a chimeric "X3TC5" ␣ 3 mutant) that associated strongly with tetraspanins were found in association with PKC. We propose that PKC-TM4SF-integrin structures represent a novel type of signaling complex. The simultaneous binding of TM4SF proteins to the extracellular domains of the integrin ␣ 3 subunit and to intracellular PKC helps to explain why the integrin ␣3 extracellular domain is needed for both intracellular PKC recruitment and PKC-dependent phosphorylation of the ␣ 3 integrin cytoplasmic tail.

Cytochrome P450 (CYP) epoxygenases convert arachidonic acid to four regioisomeric epoxyeicosatrienoic acids (EET), which exert diverse biological activities in a variety of systems. We previously reported that the CYP2J2 epoxygenase is overexpressed in human cancer tissues and cancer cell lines and that EETs enhance tumor growth, increase carcinoma cell proliferation, and prevent apoptosis of cancer cells. Herein, we report that CYP epoxygenase overexpression or EET treatment promotes tumor metastasis independent of effects on tumor growth. In four different human cancer cell lines in vitro, overexpression of CYP2J2 or CYP102 F87V with an associated increase in EET production or addition of synthetic EETs significantly induced Transwell migration (4.5-to 5.5-fold), invasion of cells (3-to 3.5-fold), cell adhesion to fibronectin, and colony formation in soft agar. In contrast, the epoxygenase inhibitor 17-ODYA or infection with the antisense recombinant adeno-associated viral vector (rAAV)-CYP2J2 vector inhibited cell migration, invasion, and adhesion with an associated reduction in EET production. CYP overexpression also enhanced metastatic potential in vivo in that rAAV-CYP2J2-infected MDA-MB-231 human breast carcinoma cells showed 60% more lung metastases in athymic BALB/c mice and enhanced angiogenesis in and around primary tumors compared with control cells. Lung metastasis was abolished by infection with the antisense rAAV-CYP2J2 vector. CYP epoxygenase overexpression or EET treatment up-regulated the prometastatic matrix metalloproteinases and CD44 and down-regulated the antimetastatic genes CD82 and nm-23. Together, these data suggest that CYP epoxygenase inhibition may represent a novel approach to prevent metastasis of human cancers. [Cancer Res 2007;67(14):6665-74]

cHuman papillomavirus type 16 (HPV16) is the primary etiologic agent for cervical cancer. The infectious entry of HPV16 into cells occurs via a so-far poorly characterized clathrin-and caveolin-independent endocytic pathway, which involves tetraspanin proteins and actin. In this study, we investigated the specific role of the tetraspanin CD151 in the early steps of HPV16 infection. We show that surface-bound HPV16 moves together with CD151 within the plane of the membrane before they cointernalize into endosomes. Depletion of endogenous CD151 did not affect binding of viral particles to cells but resulted in reduction of HPV16 endocytosis. HPV16 uptake is dependent on the C-terminal cytoplasmic region of CD151 but does not require its tyrosine-based sorting motif. Reexpression of the wild-type CD151 but not mutants affecting integrin functions restored virus internalization in CD151-depleted cells. Accordingly, short interfering RNA (siRNA) gene knockdown experiments confirmed that CD151-associated integrins (i.e., ␣3␤1 and ␣6␤1/4) are involved in HPV16 infection. Furthermore, palmitoylation-deficient CD151 did not support HPV16 cell entry. These data show that complex formation of CD151 with laminin-binding integrins and integration of the complex into tetraspanin-enriched microdomains are critical for HPV16 endocytosis.

No abstract

Upon plating on basement membrane Matrigel, NIH3T3 cells formed an anastomosing network of cord-like structures, inhibitable by anti-␣6␤1 integrin antibodies. For NIH3T3 cells transfected with human CD151 protein, the formation of a cord-like network was also inhibitable by anti-CD151 antibodies. Furthermore, CD151 and ␣6␤1 were physically associated within NIH3T3 cells. On removal of the short 8-amino acid C-terminal CD151 tail (by deletion or exchange), exogenous CD151 exerted a dominant negative effect, as it almost completely suppressed ␣6␤1-dependent cell network formation and NIH3T3 cell spreading on laminin-1 (an ␣6␤1 ligand). Importantly, mutant CD151 retained ␣6␤1 association and did not alter ␣6␤1-mediated cell adhesion to Matrigel. In conclusion, the CD151-␣6␤1 integrin complex acts as a functional unit that markedly influences cellular morphogenesis, with the CD151 tail being of particular importance in determining the "outside-in" functions of ␣6␤1-integrin that follow ligand engagement. Also, antibodies to ␣6␤1 and CD151 inhibited formation of endothelial cell cord-like networks, thus pointing to possible relevance of CD151-␣6␤1 complexes during angiogenesis. INTRODUCTIONStudies of integrin-dependent adhesion, migration, and signaling have focused largely on integrin ligand binding sites (Plow et al., 2000) and on cytoplasmic domains (Liu et al., 2000). Cytoplasmic domain perturbations alter ligand binding ("inside-out" signaling) and ligand binding triggers long-range alterations in cytoplasmic domain interactions ("outside-in" signaling). Integrin functions are modulated also by lateral associations with other transmembrane proteins (Hemler, 1998;Woods and Couchman, 2000). As shown here, outside-in signaling through ␣6␤1 integrin is markedly influenced by its lateral association with CD151, a transmembrane-4 superfamily (TM4SF, tetraspanin) protein.Tetraspanin proteins contain two extracellular loops, four hydrophobic transmembrane domains, and two short cytoplasmic tails. Tetraspanins regulate membrane fusion, trafficking, cell motility, and tumor metastasis (Wright and Tomlinson, 1994;. Tetraspanins form multimolecular complexes with many other transmembrane proteins, including integrins (Hemler et al., 1996;Hemler, 1998). Despite several reports of tetraspanin-protein complexes, only a few have documented functional relevance. For example, results from CD81-null mice support the relevance of CD81-CD19 association Miyazaki et al., 1997;Tsitsikov et al., 1997), CD9 influences the activity of associated HB-EGF (Iwamoto et al., 1994), and antibodies to CD81 and CD151 inhibit the functions of associated integrins (Domanico et al., 1997;Yánez-Mó et al., 1998;Yauch et al., 1998;Stipp and Hemler, 2000). Notably, anti-CD81 and anti-CD151 antibodies inhibited neurite outgrowth only when associated ␣3␤1 integrin was engaged with ligand (Stipp and Hemler, 2000).Among tetraspanin complexes, the CD151-␣3␤1 integrin complex has unusually high stoichiometry, proximity, and stability. A specific site in CD151'...

No abstract

Coronavirus disease 2019 (COVID-19) is a global pandemic which has caused numerous deaths worldwide. The present study investigated the roles of hypoproteinemia in the clinical outcome and liver dysfunction of COVID-19 patients. In this retrospective study, we extracted data from 2,623 clinically confirmed adult COVID-19 patients (≥18 years old) between January 29, 2020 and March 6, 2020 in Tongji Hospital, Wuhan, China. The patients were divided into three groups-non-critically ill, critically ill, and death groups-in accordance with the Chinese Clinical Guideline for COVID-19. Serum albumin, low-density lipoproteins cholesterol (LDL-C), and high-density lipoproteins cholesterol (HDL-C) concentrations and inflammatory cytokines levels were measured and compared among these three groups. The median age of these 2,623 patients was 64 years old (interquartile range (IQR), 52-71). Among the patients enrolled in the study, 2,008 (76.6%) were diagnosed as non-critically ill and 615 (23.4%) were critically ill patients, including 383 (14.6%) critically ill survivors and 232 (8.8%) critically ill deaths in the hospital. Marked hypoalbuminemia occurred in 38.2%, 71.2%, and 82.4% patients in non-critically ill, critically ill, and death groups, respectively, on admission and 45.9%, 77.7%, and 95.6% of these three groups, respectively, during hospitalization. We also discovered that serum low-density lipoprotein (LDL) and HDL levels were significantly lower in critically ill and death groups compared to non-critically ill group. Meanwhile, the patients displayed dramatically elevated levels of serum inflammatory factors, while a markedly prolonged activated partial thromboplastin time (APTT) in critically ill patients reflected coagulopathy. This study suggests that COVID-19-induced cytokine storm causes hepatotoxicity and subsequently critical hypoalbuminemia, which are associated with exacerbation of disease-associated inflammatory responses and progression of the disease and ultimately leads to death for some critically ill patients.

Regulation of cell migration is an important feature of tetraspanin CD151. Although it is well established that CD151 physically associates with integrins, the mechanism by which CD151 regulates integrin-dependent cell migration is basically unknown. Given the fact that CD151 is localized in both the plasma membrane and intracellular vesicles, we found that CD151 and its associated ␣3␤1, ␣5␤1, and ␣6␤1 integrins undergo endocytosis and accumulate in the same intracellular vesicular compartments. CD151 contains a YRSL sequence, a YXX type of endocytosis/sorting motif, in its C-terminal cytoplasmic domain. Mutation of this motif markedly attenuated CD151 internalization. The loss of CD151 trafficking completely abrogated CD151-promoted cell migration on extracellular matrices such as laminin and diminished the internalization of its associated integrins, indicating a critical role for integrin trafficking in regulating cell motility. In conclusion, the YXX motif-mediated internalization of CD151 promotes integrin-dependent cell migration by modulating the endocytosis and/or vesicular trafficking of its associated integrins.