Overexpression of atypical protein kinase C in HeLa cells facilitates macropinocytosis via Src activation

A Coxsackievirus B1-mediated nonlytic Extracellular Vesicle-to-cell mechanism of virus transmission and its possible control through modulation of EV release

Like most non-enveloped viruses, CVB1 mainly uses cell lysis to spread. Details of a nonlytic virus transmission remain unclear. Extracellular Vesicles (EVs) transfer biomolecules between cells. We show that CVB1 entry into HeLa cells results in apoptosis and release of CVB1-induced 'medium-sized' EVs (CVB1i-mEVs). These mEVs (100-300 nm) harbour CVB1 as shown by immunoblotting with anti-CVB1-antibody; viral capsids were detected by transmission electron microscopy and RT-PCR revealed CVB1 RNA. The percentage of mEVs released from CVB1-infected HeLa cells harbouring virus was estimated from TEM at 34 %. Inhibition of CVB1i-mEV production, with calpeptin or siRNA knockdown of CAPNS1 in HeLa cells limited spread of CVB1 suggesting these vesicles disseminate CVB1 virions to new host cells by a nonlytic EV-to-cell mechanism. This was confirmed by detecting CVB1 virions inside HeLa cells after co-culture with CVB1i-mEVs; EV release may also prevent apoptosis of infected cells whilst spreading apoptosis to secondary sites of infection.

Rab2 stimulates LC3 lipidation on secretory membranes by noncanonical autophagy

The Golgi complex is a highly dynamic organelle that regulates various cellular activities and yet maintains a distinct structure. Multiple proteins participate in Golgi structure/organization including the small GTPase Rab2. Rab2 is found on the cis/medial Golgi compartments and the endoplasmic reticulum-Golgi intermediate compartment. Interestingly, Rab2 gene amplification occurs in a wide range of human cancers and Golgi morphological alterations are associated with cellular transformation. To learn how Rab2 'gain of function' influences the structure/activity of membrane compartments in the early secretory pathway that may contribute to oncogenesis, NRK cells were transfected with Rab2B cDNA. We found that Rab2B overexpression had a dramatic effect on the morphology of pre- and early Golgi compartments that resulted in a decreased transport rate of VSV-G in the early secretory pathway. We monitored the cells for the autophagic marker protein LC3 based on the findings that depressed membrane trafficking affects homeostasis. Morphological and biochemical studies confirmed that Rab2 ectopic expression stimulated LC3-lipidation on Rab2-containing membranes that was dependent on GAPDH and utilized a non-canonical LC3-conjugation mechanism that is nondegradative. Golgi structural alterations are associated with changes in Golgi-associated signalling pathways. Indeed, Rab2 overexpressing cells had elevated Src activity. We propose that increased Rab2 expression facilitates cis Golgi structural changes that are maintained and tolerated by the cell due to LC3 tagging, and subsequent membrane remodeling triggers Golgi associated signaling pathways that may contribute to oncogenesis.

An albumin‑binding domain and targeting peptide‑based recombinant protein and its enediyne‑integrated analogue exhibit directional delivery and potent inhibitory activity on pancreatic cancer with K‑ras mutation

Efficient enrichment and transmembrane transport of cytotoxic reagents are considered to be effective strategies to increase the efficiency and selectivity of antitumor drugs targeting solid tumors. In the present study, a recombinant protein ABD‑LDP‑Ec consisting of the albumin‑binding domain (ABD), the apoprotein (LDP) of lidamycin (LDM) and an EGFR‑targeting oligopeptide (Ec) was prepared by DNA recombination and bacterial fermentation, and was integrated with the enediyne chromophore (AE) of lidamycin to generate its enediyne‑integrated analogue ABD‑LDP‑Ec‑AE. ABD‑LDP‑Ec exhibited high binding capacity to both albumin and EGFR‑positive pancreatic cancer cells, and was internalized into the cytoplasm through receptor‑mediated endocytosis and albumin‑driven macropinocytosis of K‑ras mutant cells. In animal experiments, ABD‑LDP‑Ec demonstrated notable selective distribution in pancreatic carcinoma xenografts by passive targeting of albumin captured in the blood and was retained in the tumor for 48 h. ABD‑LDP‑Ec and ABD‑LDP‑Ec‑AE exhibited inhibitory activity in cell proliferation and AsPC‑1 xenograft growth, and ABD‑LDP‑Ec‑AE increased the tumor growth inhibition rate by 20% compared with natural LDM. The results indicated that the introduction of ABD‑based multi‑functional drug delivery may be an effective approach to improve the efficacy of antitumor drugs, especially for K‑ras mutant cancers.

Varroa destructor parasitism has a greater effect on proteome changes than the deformed wing virus and activates TGF-β signaling pathways

Honeybee workers undergo metamorphosis in capped cells for approximately 13 days before adult emergence. During the same period, Varroa mites prick the defenseless host many times. We sought to identify proteome differences between emerging Varroa-parasitized and parasite-free honeybees showing the presence or absence of clinical signs of deformed wing virus (DWV) in the capped cells. A label-free proteomic analysis utilizing nanoLC coupled with an Orbitrap Fusion Tribrid mass spectrometer provided a quantitative comparison of 2316 protein hits. Redundancy analysis (RDA) showed that the combination of Varroa parasitism and DWV clinical signs caused proteome changes that occurred in the same direction as those of Varroa alone and were approximately two-fold higher. Furthermore, proteome changes associated with DWV signs alone were positioned above Varroa in the RDA. Multiple markers indicate that Varroa activates TGF-β-induced pathways to suppress wound healing and the immune response and that the collective action of stressors intensifies these effects. Furthermore, we indicate JAK/STAT hyperactivation, p53-BCL-6 feedback loop disruption, Wnt pathway activation, Wnt/Hippo crosstalk disruption, and NF-κB and JAK/STAT signaling conflict in the Varroa–honeybee–DWV interaction. These results illustrate the higher effect of Varroa than of DWV at the time of emergence. Markers for future research are provided.

GRP75 modulates oncogenic Dbl-driven endocytosis derailed via the CHIP-mediated ubiquitin degradation pathway

Chaperone-assisted proteasome degradation of oncogenic protein acts as an upstream signal controlling tumorigenesis and progression. The understanding of the co-regulation of chaperone and oncoprotein of endocytosis pathways is extremely limited. In this study, we showed for the first time that proto-Dbl (dbl proto-oncogene product) is co-enriched with mitochondrial chaperone GRP75 in endocytosis vesicles from ovarian cancer cells. onco-Dbl, produced by oncogenic mutation/degradation of proto-Dbl, markedly enhanced cellular macropinocytosis but suppressed clathrin-mediated endocytosis and clathrin-independent endocytosis pathways, presenting a derailed endocytosis phenotype. GRP75 was associated with proto-Dbl inside cells and modulated Dbl-driven endocytosis derailed by a co-regulatory mode. In spite of not being a component of the Hsc70/Hsp90/proto-Dbl complex, the degradation of proto-Dbl was promoted by GRP75 through the CHIP-mediated ubiquitin–proteasome pathway, of which GRP75 acts as a cooperator with CHIP but also acts as a competitor to Hsc70 and Hsp90 in the multiple chaperones-assisted pro-folding/pro-degradation machinery. Knockdown or inhibition of GRP75 attenuated proto-Dbl degradation and reduced the onco-Dbl level, which differentially impaired Rho GTPases activation and therefore shifted the endocytosis-derailed phenotype. Our data uncovered a novel GRP75-Dbl endocytosis regulatory axis and provided an alternative using chaperone inhibitor to shut down the oncoprotein-driven endocytosis derailment mechanism.

A Macropinocytosis-Intensifying Albumin Domain-Based scFv Antibody and Its Conjugate Directed against K-Ras Mutant Pancreatic Cancer

Enhanced macropinocytosis has been found in K-Ras mutant pancreatic cancer cells, through which albumin can massively enter into the K-Ras-driven cancer cells, suggesting its role in serving as a macropinocytosis-intensifying drug delivery carrier. In the present study, a novel recombinant protein Fv-LDP-D3 and its reconstituted analogue Fv-LDP-D3-AE were designed and prepared. Fv is the fragment of an anti-EGFR antibody, D3 is the domain III of human serum albumin (HSA), LDP is the apoprotein of the antitumor antibiotic lidamycin (LDM), and AE is an extremely cytotoxic enediyne chromophore derived from LDM. As shown, the recombinant protein Fv-LDP-D3 presented intensive and selective binding capacity to pancreatic cancer cells and inhibited cell proliferation by blocking EGFR signaling. Moreover, Fv-LDP-D3 showed prominent tumor imaging in pancreatic carcinoma xenograft. The reconstituted, enediyne-integrated analogue Fv-LDP-D3-AE displayed highly potent cytotoxicity to pancreatic cancer cells through apoptosis induction and G2/M arrest. Fv-LDP-D3 and Fv-LDP-D3-AE markedly inhibited the tumor growth of the pancreatic carcinoma AsPC-1 xenograft. Study results indicated that the novel recombinant protein displays both EGFR-targeting and macropinocytosis-intensifying attributes, presenting a new format of scFv antibody that integrates with albumin domain III. It might be a feasible strategy to develop targeted drugs for K-Ras mutant pancreatic cancer.

A recombinantly tailored β-defensin that displays intensive macropinocytosis-mediated uptake exerting potent efficacy against K-Ras mutant pancreatic cancer

K-Ras mutant pancreatic cancer cells display intensive macropinocytosis, indicating that this process may be exploited in the design of anticancer targeted therapies. In this study, we constructed a macropinocytosis-oriented recombinantly tailored defensin (DF-HSA) which consists of human β-defensin-2 (DF) and human serum albumin (HSA). The macropinocytosis intensity and cytotoxicity of DF-HSA were investigated in K-Ras mutant MIA PaCa-2 cells and wild-type BxPC-3 cells. As found, the DF-HSA uptake in MIA PaCa-2 cells was much higher than that in wild-type BxPC-3 cells. Correspondingly, the cytotoxicity of DF-HSA to MIA PaCa-2 cells was more potent than that to BxPC-3 cells. In addition, the cytotoxicity of DF-HSA was much stronger than that of β-defensin HBD2. DF-HSA suppressed cancer cell proliferation and induced mitochondrial pathway apoptosis. Notably, DF-HSA significantly inhibited the growth of human pancreatic carcinoma MIA PaCa-2 xenograft in athymic mice at well tolerated dose. By in vivo imaging, DF-HSA displayed a prominent accumulation in the tumor. The study indicates that the recombinantly tailored β-defensin can intensively enter into the K-Ras mutant pancreatic cancer cells through macropinocytosis-mediated process and exert potent therapeutic efficacy against the pancreatic carcinoma xenograft. The novel format of β-defensin may play an active role in macropinocytosis-mediated targeting therapy.

GAPDH binds Akt to facilitate cargo transport in the early secretory pathway

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) undergoes numerous post-translational modifications, which impart new function and influence intracellular location. For example, atypical PKC ι/λ phosphorylates GAPDH that locates to vesicular tubular clusters and is required for retrograde membrane trafficking in the early secretory pathway. GAPDH is also required in the endocytic pathway; substitution of Pro²³⁴ to Ser (Pro²³⁴Ser) rendered CHO cells defective in endocytosis. To determine if GAPDH (Pro²³⁴Ser) could inhibit endoplasmic reticulum to Golgi trafficking, we introduced the recombinant mutant enzyme into several biochemical and morphological transport assays. The mutant protein efficiently blocked vesicular stomatitis virus-G protein transport. Because GAPDH binds to microtubules (MTs), we evaluated MT binding and MT intracellular distribution in the presence of the mutant. Although these properties were not changed relative to wild-type, GAPDH (Pro²³⁴Ser) altered Golgi complex morphology. We determined that the GAPDH point mutation disrupted association between the enzyme and the serine/threonine kinase Akt. Interestingly Rab1, which functions in anterograde-directed trafficking, stimulates GAPDH-Akt association with membranes in a quantitative binding assay. In contrast, Rab2 does not stimulate GAPDH-Akt membrane binding but instead recruits GAPDH-aPKC. We propose a mechanism whereby the association of GAPDH with Akt or with aPKC serves as a switch to discriminate between anterograde directed cargo and recycling cargo retrieved back to the ER, respectively.

Differential signaling during macropinocytosis in response to M-CSF and PMA in macrophages

The cellular movements that construct a macropinosome have a corresponding sequence of chemical transitions in the cup-shaped region of plasma membrane that becomes the macropinosome. To determine the relative positions of type I phosphatidylinositol 3-kinase (PI3K) and phospholipase C (PLC) in this pathway, we analyzed macropinocytosis in macrophages stimulated by the growth factor macrophage-colony-stimulating factor (M-CSF) and by the diacylglycerol (DAG) analog phorbol 12-myristate 13-acetate (PMA). In cells stimulated with M-CSF, microscopic imaging of fluorescent probes for intracellular lipids indicated that the PI3K product phosphatidylinositol (3,4,5)-trisphosphate (PIP3) appeared in cups just prior to DAG. We then tested the hypothesis that PMA and DAG function after PI3K and prior to Ras and protein kinase C (PKC) during macropinosome formation in macrophages. Although the PI3K target Akt was activated by M-CSF, the Akt inhibitor MK-2206 did not inhibit macropinocytosis. The phospholipase C (PLC) inhibitor U73122 blocked macropinocytosis by M-CSF but not PMA. Macropinocytosis in response to M-CSF and PMA was inhibited by the Ras inhibitor farnesyl thiosalicylate (FTS), by the PKC inhibitor Calphostin C and by the broad specificity inhibitor rottlerin. These studies support a model in which M-CSF stimulates PI3K in macropinocytic cups, and the resulting increase in PIP3 activates PLC, which in turn generates DAG necessary for activation of PKC, Ras and the late stages of macropinosome closure.