Rho GTPases play central roles in numerous cellular processes, including cell motility, cell polarity, and cell cycle progression, by regulating actin cytoskeletal dynamics and cell adhesion. Dysregulation of Rho GTPase signaling is observed in a broad range of human cancers, and is associated with cancer development and malignant phenotypes, including metastasis and chemoresistance. Rho GTPase activity is precisely controlled by guanine nucleotide exchange factors, GTPase-activating proteins, and guanine nucleotide dissociation inhibitors. Recent evidence demonstrates that it is also regulated by post-translational modifications, such as phosphorylation, ubiquitination, and sumoylation. Here, we review the current knowledge on the role of Rho GTPases, and the precise mechanisms controlling their activity in the regulation of cancer progression. In addition, we discuss targeting strategies for the development of new drugs to improve cancer therapy.

Sepsis is a life-threatening condition that is caused by an abnormal immune response to infection and can lead to tissue damage, organ failure, and death. Erastin is a small molecule capable of initiating ferroptotic cell death in cancer cells. However, the function of erastin in the inflammatory response during sepsis remains unknown. Here, we showed that erastin ameliorates septic shock induced by cecal ligation and puncture or lipopolysaccharides (LPS) in mice, which was associated with a reduced production of inflammatory mediators such as nitric oxide, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. Pretreatment with erastin in bone marrow-derived macrophages (BMDMs) significantly attenuated the expression of inducible nitric oxide synthase, cyclooxygenase-2, TNF-α, and IL-1β mRNA in response to LPS treatment. Furthermore, we also showed that erastin suppresses phosphorylation of IκB kinase β, phosphorylation and degradation of IκBα, and nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in LPS-stimulated BMDMs. Our findings suggest that erastin attenuates the inflammatory response by suppressing the NF-κB signaling pathway, resulting in inhibition of sepsis development. This study provides new insights regarding the potential therapeutic properties of erastin in sepsis.

Ubiquitination is a post-translational modification involving the covalent attachment of a ubiquitin moiety to a lysine residue and is known to regulate the localization, activity, and stability of the substrate proteins [1,2]. There are two types of E3 ubiquitin ligases, namely, the RING (really interesting new gene) and HECT (homologous to the E6AP carboxyl terminus) families [3]. Cullins are a family of hydrophobic scaffold proteins that provide support for ubiquitin ligases. They share a homologous C-terminus that binds to the RING-box protein (Rbx1), but diverge at the N-terminal substrate recruiting domain [4,5]. Members of a subclass of the RING protein family interact with Cullins to create the aptly-named Cullin-RING ligases (CRLs), whose ubiquitin ligase activities are involved in many biological processes. Cullin 3-RING ligases (CRL3s) typically consist of the scaffold protein Cullin 3 (CUL3), Rbx1, and a Bric-a-brac/Tramtrack/Broad (BTB) protein. These component proteins collaborate in the ubiquitination of substrate proteins [6][7][8].Rho GTPases are involved in various cellular processes, including cell motility, adhesion, and proliferation [9]. They act as molecular switches, cycling between an inactive guanosine diphosphate (GDP)-bound form in the cytoplasm and an active guanosine triphosphate (GTP)-bound form in the membrane [10]. This cycling is tightly regulated by Rho guanine nucleotide exchange factors (RhoGEFs), i.e., proteins that promote the exchange of GDP for GTP, and Rho GTPase-activating proteins (RhoGAPs), which catalyze intrinsic GTP hydrolysis, thereby inactivating Rho GTPases [11,12]. Rho guanine nucleotide dissociation inhibitors (RhoGDIs) also play a key role in regulating the activities of Rho GTPase family proteins [13], as they bind to most GDP-bound Rho GTPases, preventing them from binding to RhoGEFs or their effector molecules [14]. Thus, they are considered negative regulators of Rho GTPases. However, RhoGDIs can also function as chaperons for Rho GTPases, regulating the delivery and extraction of Rho GTPases to their action sites [15]. When Rho GTPases dissociate from RhoGDIs, they can enter the membrane, where they are activated by RhoGEFs. Re-association with RhoGDIs is necessary for the recycling of Rho GTPases [16,17].There are three members of the RhoGDI family in mammals, namely, RhoGDI1, RhoGDI2, and RhoGDI3. RhoGDI1 is ubiquitously expressed in all mammalian organs; whereas RhoGDI2 is hematopoietic cell-specific, and RhoGDI3 is expressed in the brain, kidney, and testis [18][19][20]. Accumulating evidence shows that RhoGDI1 is involved in tumorigenesis and cancer progression. Even though anomalous RhoGDI1 expression has been detected in a variety of human cancers, the exact type of dysregulation is dependent on cancer type [21,22]. In Rho guanine nucleotide dissociation inhibitor 1 (RhoGDI1) plays important roles in numerous cellular processes, including cell motility, adhesion, and proliferation, by regulating the activity of Rho GTPases. Its expression is altere...

Interleukin-21 is a common γ-chain cytokine that controls the immune responses of B cells, T cells, and natural killer cells. Targeting IL-21 to strengthen the immune system is promising for the development of vaccines as well as anti-infection and anti-tumor therapies. However, the practical application of IL-21 is limited by the high production cost. In this study, we improved IL-21 production by codon optimization and selection of appropriate signal peptide in CHO-K1 cells. Codon-optimized or non-optimized human IL-21 was stably transfected into CHO-K1 cells. IL-21 expression was 10-fold higher for codon-optimized than non-optimized IL-21. We fused five different signal peptides to codon-optimized mature IL-21 and evaluated their effect on IL-21 production. The best result (a 3-fold increase) was obtained using a signal peptide derived from human azurocidin. Furthermore, codon-optimized IL-21 containing the azurocidin signal peptide promoted IFN-γ secretion and STAT3 phosphorylation in NK-92 cells similar to codon-optimized IL-21 containing original signal peptide. Collectively, these results indicate that codon optimization and azurocidin signal peptides provide an efficient approach for the high-level production of IL-21 as a biopharmaceutical.

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Kallikrein-related peptidase (KLK)6 is associated with inflammatory diseases and neoplastic progression. KLK6 is aberrantly expressed in several solid tumors and regulates cancer development, metastatic progression, and drug resistance. However, the function of KLK6 in the tumor microenvironment remains unclear. This study aimed to determine the role of KLK6 in the tumor microenvironment. Here, we uncovered the mechanism underlying KLK6-mediated cross-talk between cancer cells and macrophages. Compared with wild-type mice, KLK6−/− mice showed less tumor growth and metastasis in the B16F10 melanoma and Lewis lung carcinoma (LLC) xenograft model. Mechanistically, KLK6 promoted the secretion of tumor necrosis factor-alpha (TNF-α) from macrophages via the activation of protease-activated receptor-1 (PAR1) in an autocrine manner. TNF-α secreted from macrophages induced the release of the C-X-C motif chemokine ligand 1 (CXCL1) from melanoma and lung carcinoma cells in a paracrine manner. The introduction of recombinant KLK6 protein in KLK6−/− mice rescued the production of TNF-α and CXCL1, tumor growth, and metastasis. Inhibition of PAR1 activity suppressed these malignant phenotypes rescued by rKLK6 in vitro and in vivo. Our findings suggest that KLK6 functions as an important molecular link between macrophages and cancer cells during malignant progression, thereby providing opportunities for therapeutic intervention.