The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z-α1-antitrypsin.

α1-Antitrypsin is a serine protease inhibitor produced in the liver that is responsible for the regulation of pulmonary inflammation. The commonest pathogenic gene mutation yields Z-α1-antitrypsin, which has a propensity to self-associate forming polymers that become trapped in inclusions of endoplasmic reticulum (ER). It is unclear whether these inclusions are connected to the main ER network in Z-α1-antitrypsin-expressing cells. Using live cell imaging, we found that despite inclusions containing an immobile matrix of polymeric α1-antitrypsin, small ER resident proteins can diffuse freely within them. Inclusions have many features to suggest they represent fragmented ER, and some are physically separated from the tubular ER network, yet we observed cargo to be transported between them in a cytosol-dependent fashion that is sensitive to N-ethylmaleimide and dependent on Sar1 and sec22B. We conclude that protein recycling occurs between ER inclusions despite their physical separation.-Dickens, J. A., Ordóñez, A., Chambers, J. E., Beckett, A. J., Patel, V., Malzer, E., Dominicus, C. S., Bradley, J., Peden, A. A., Prior, I. A., Lomas, D. A., Marciniak, S. J. The endoplasmic reticulum remains functionally connected by vesicular transport after its fragmentation in cells expressing Z-α1-antitrypsin.

Autism-associated R451C mutation in neuroligin3 leads to activation of the unfolded protein response in a PC12 Tet-On inducible system.

Several forms of monogenic heritable autism spectrum disorders are associated with mutations in the neuroligin genes. The autism-linked substitution R451C in neuroligin3 induces local misfolding of its extracellular domain, causing partial retention in the ER (endoplasmic reticulum) of expressing cells. We have generated a PC12 Tet-On cell model system with inducible expression of wild-type or R451C neuroligin3 to investigate whether there is activation of the UPR (unfolded protein response) as a result of misfolded protein retention. As a positive control for protein misfolding, we also expressed the mutant G221R neuroligin3, which is known to be completely retained within the ER. Our data show that overexpression of either R451C or G221R mutant proteins leads to the activation of all three signalling branches of the UPR downstream of the stress sensors ATF6 (activating transcription factor 6), IRE1 (inositol-requiring enzyme 1) and PERK [PKR (dsRNA-dependent protein kinase)-like endoplasmic reticulum kinase]. Each branch displayed different activation profiles that partially correlated with the degree of misfolding caused by each mutation. We also show that up-regulation of BiP (immunoglobulin heavy-chain-binding protein) and CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein] was induced by both mutant proteins but not by wild-type neuroligin3, both in proliferative cells and cells differentiated to a neuron-like phenotype. Collectively, our data show that mutant R451C neuroligin3 activates the UPR in a novel cell model system, suggesting that this cellular response may have a role in monogenic forms of autism characterized by misfolding mutations.

Pyk2 and Megakaryocytes Regulate Osteoblast Differentiation and Migration Via Distinct and Overlapping Mechanisms.

Osteoblast differentiation and migration are necessary for bone formation during bone remodeling. Mice lacking the proline-rich tyrosine kinase Pyk2 (Pyk2-KO) have increased bone mass, in part due to increased osteoblast proliferation. Megakaryocytes (MKs), the platelet-producing cells, also promote osteoblast proliferation in vitro and bone-formation in vivo via a pathway that involves Pyk2. In the current study, we examined the mechanism of action of Pyk2, and the role of MKs, on osteoblast differentiation and migration. We found that Pyk2-KO osteoblasts express elevated alkaline phosphatase (ALP), type I collagen and osteocalcin mRNA levels as well as increased ALP activity, and mineralization, confirming that Pyk2 negatively regulates osteoblast function. Since Pyk2 Y402 phosphorylation is important for its catalytic activity and for its protein-scaffolding functions, we expressed the phosphorylation-mutant (Pyk2(Y402F) ) and kinase-mutant (Pyk2(K457A) ) in Pyk2-KO osteoblasts. Both Pyk2(Y402F) and Pyk2(K457A) reduced ALP activity, whereas only kinase-inactive Pyk2(K457A) inhibited Pyk2-KO osteoblast migration. Consistent with a role for Pyk2 on ALP activity, co-culture of MKs with osteoblasts led to a decrease in the level of phosphorylated Pyk2 (pY402) as well as a decrease in ALP activity. Although, Pyk2-KO osteoblasts exhibited increased migration compared to wild-type osteoblasts, Pyk2 expression was not required necessary for the ability of MKs to stimulate osteoblast migration. Together, these data suggest that osteoblast differentiation and migration are inversely regulated by MKs via distinct Pyk2-dependent and independent signaling pathways. Novel drugs that distinguish between the kinase-dependent or protein-scaffolding functions of Pyk2 may provide therapeutic specificity for the control of bone-related diseases.

The cytotoxic action of BCI is not dependent on its stated DUSP1 or DUSP6 targets in neuroblastoma cells.

Neuroblastoma (NB) is a heterogeneous cancer of the sympathetic nervous system, which accounts for 7-10% of paediatric malignancies worldwide. Due to the lack of targetable molecular aberrations in NB, most treatment options remain relatively nonspecific. Here, we investigated the therapeutic potential of BCI, an inhibitor of DUSP1 and DUSP6, in cultured NB cells. BCI was cytotoxic in a range of NB cell lines and induced a short-lived activation of the AKT and stress-inducible MAP kinases, although ERK phosphorylation was unaffected. Furthermore, a phosphoproteomic screen identified significant upregulation of JNK signalling components and suppression in mTOR and R6K signalling. To assess the specificity of BCI, CRISPR-Cas9 was employed to introduce insertions and deletions in the DUSP1 and DUSP6 genes. Surprisingly, BCI remained fully cytotoxic in NB cells with complete loss of DUSP6 and partial depletion of DUSP1, suggesting that BCI exerts cytotoxicity in NB cells through a complex mechanism that is unrelated to these phosphatases. Overall, these data highlight the risk of using an inhibitor such as BCI as supposedly specific DUSP1/6, without understanding its full range of targets in cancer cells.

Inactivation of Ppp1r15a minimises weight gain and insulin resistance during caloric excess in female mice.

Phosphorylation of the translation initiation factor eIF2α within the mediobasal hypothalamus is known to suppress food intake, but the role of the eIF2α phosphatases in regulating body weight is poorly understood. Mice deficient in active PPP1R15A, a stress-inducible eIF2α phosphatase, are healthy and more resistant to endoplasmic reticulum stress than wild type controls. We report that when female Ppp1r15a mutant mice are fed a high fat diet they gain less weight than wild type littermates owing to reduced food intake. This results in healthy leaner Ppp1r15a mutant animals with reduced hepatic steatosis and improved insulin sensitivity, albeit with a possible modest defect in insulin secretion. By contrast, no weight differences are observed between wild type and Ppp1r15a deficient mice fed a standard diet. We conclude that female mice lacking the C-terminal PP1-binding domain of PPP1R15A show reduced dietary intake and preserved glucose tolerance. Our data indicate that this results in reduced weight gain and protection from diet-induced obesity.

Pyk2 deficiency potentiates osteoblast differentiation and mineralizing activity in response to estrogen or raloxifene.

Bone remodeling is controlled by the actions of bone-degrading osteoclasts and bone-forming osteoblasts (OBs). Aging and loss of estrogen after menopause affects bone mass and quality. Estrogen therapy, including selective estrogen receptor modulators (SERMs), can prevent bone loss and increase bone mineral density in post-menopausal women. Although investigations of the effects of estrogen on osteoclast activity are well advanced, the mechanism of action of estrogen on OBs is still unclear. The proline-rich tyrosine kinase 2 (Pyk2) is important for bone formation and female mice lacking Pyk2 (Pyk2-KO) exhibit elevated bone mass, increased bone formation rate and reduced osteoclast activity. Therefore, in the current study, we examined the role of estrogen signaling on the mechanism of action of Pyk2 in OBs. As expected, Pyk2-KO OBs showed significantly higher proliferation, matrix formation, and mineralization than WT OBs. In addition we found that Pyk2-KO OBs cultured in the presence of either 17ß-estradiol (E2) or raloxifene, a SERM used for the treatment of post-menopausal osteoporosis, showed a further robust increase in alkaline phosphatase (ALP) activity and mineralization. We examined the possible mechanism of action and found that Pyk2 deletion promotes the proteasome-mediated degradation of estrogen receptor α (ERα), but not estrogen receptor ß (ERß). As a consequence, E2 signaling via ERß was enhanced in Pyk2-KO OBs. In addition, we found that Pyk2 deletion and E2 stimulation had an additive effect on ERK phosphorylation, which is known to stimulate cell differentiation and survival. Our findings suggest that in the absence of Pyk2, estrogen exerts an osteogenic effect on OBs through altered ERα and ERß signaling. Thus, targeting Pyk2, in combination with estrogen or raloxifene, may be a novel strategy for the prevention and/or treatment of bone loss diseases.

Prospective Analysis of Adoptive TIL Therapy in Patients with Metastatic Melanoma: Response, Impact of Anti-CTLA4, and Biomarkers to Predict Clinical Outcome.

Purpose: Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TIL) has consistently demonstrated clinical efficacy in metastatic melanoma. Recent widespread use of checkpoint blockade has shifted the treatment landscape, raising questions regarding impact of these therapies on response to TIL and appropriate immunotherapy sequence.Patients and Methods: Seventy-four metastatic melanoma patients were treated with autologous TIL and evaluated for clinical response according to irRC, overall survival, and progression-free survival. Immunologic factors associated with response were also evaluated.Results: Best overall response for the entire cohort was 42%; 47% in 43 checkpoint-naïve patients, 38% when patients were exposed to anti-CTLA4 alone (21 patients) and 33% if also exposed to anti-PD1 (9 patients) prior to TIL ACT. Median overall survival was 17.3 months; 24.6 months in CTLA4-naïve patients and 8.6 months in patients with prior CTLA4 blockade. The latter patients were infused with fewer TIL and experienced a shorter duration of response. Infusion of higher numbers of TIL with CD8 predominance and expression of BTLA correlated with improved response in anti-CTLA4 naïve patients, but not in anti-CTLA4 refractory patients. Baseline serum levels of IL9 predicted response to TIL ACT, while TIL persistence, tumor recognition, and mutation burden did not correlate with outcome.Conclusions: This study demonstrates the deleterious effects of prior exposure to anti-CTLA4 on TIL ACT response and shows that baseline IL9 levels can potentially serve as a predictive tool to select the appropriate sequence of immunotherapies. Clin Cancer Res; 24(18); 4416-28. ©2018 AACR.

New Concepts in Alpha-1 Antitrypsin Deficiency Disease Mechanisms.

Alpha-1 antitrypsin deficiency is predominantly caused by point mutations that alter the protein's folding. These mutations fall into two broad categories: those that destabilize the protein dramatically and lead to its post-translational degradation and those that affect protein structure more subtly to promote protein polymerization within the endoplasmic reticulum (ER). This distinction is important because it determines the cell's response to each mutant. The severely misfolded mutants trigger an unfolded protein response (UPR) that promotes improved protein folding but can kill the cell in the chronic setting. In contrast, mutations that permit polymer formation fail to activate the UPR but instead promote a nuclear factor-κB-mediated ER overload response. The ability of polymers to increase a cell's sensitivity to ER stress likely explains apparent inconsistencies in the alpha-1 antitrypsin-signaling literature that have linked polymers with the UPR. In this review we discuss the use of mutant serpins to dissect each signaling pathway.

Actin dynamics tune the integrated stress response by regulating eukaryotic initiation factor 2α dephosphorylation.

Four stress-sensing kinases phosphorylate the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) to activate the integrated stress response (ISR). In animals, the ISR is antagonised by selective eIF2α phosphatases comprising a catalytic protein phosphatase 1 (PP1) subunit in complex with a PPP1R15-type regulatory subunit. An unbiased search for additional conserved components of the PPP1R15-PP1 phosphatase identified monomeric G-actin. Like PP1, G-actin associated with the functional core of PPP1R15 family members and G-actin depletion, by the marine toxin jasplakinolide, destabilised the endogenous PPP1R15A-PP1 complex. The abundance of the ternary PPP1R15-PP1-G-actin complex was responsive to global changes in the polymeric status of actin, as was its eIF2α-directed phosphatase activity, while localised G-actin depletion at sites enriched for PPP1R15 enhanced eIF2α phosphorylation and the downstream ISR. G-actin's role as a stabilizer of the PPP1R15-containing holophosphatase provides a mechanism for integrating signals regulating actin dynamics with stresses that trigger the ISR.

The deubiquitylase USP15 stabilizes newly synthesized REST and rescues its expression at mitotic exit.

Reversible ubiquitylation of proteins contributes to their integrity, abundance and activity. The RE1-silencing transcription factor (REST) plays key physiological roles and is dysregulated in a spectrum of disease. It is rapidly turned over and is phosphorylated, polyubiquitylated and degraded en masse during neuronal differentiation and cell cycle progression. Through siRNA screening we identified the deubiquitylase USP15 as a key regulator of cellular REST. Both antagonism of REST polyubiquitylation and rescue of endogenous REST levels are dependent on the deubiquitylase activity of USP15. However, USP15 depletion does not destabilize pre-existing REST, but rather specifically impairs de novo REST synthesis. Indeed, we find that a small fraction of endogenous USP15 is associated with polysomes. In accordance with these findings, USP15 does not antagonize the degradation of phosphorylated REST at mitosis. Instead it is required for the rapid accumulation of newly synthesized REST on mitotic exit, thus playing a key role in its cell cycle oscillations. Importantly, this study reveals a novel role for a DUB in specifically promoting new protein synthesis.