CaM kinase II regulation of CRHSP-28 phosphorylation in cultured mucosal T84 cells

Deficient Endoplasmic Reticulum Acetyl-CoA Import in Pancreatic Acinar Cells Leads to Chronic Pancreatitis

BACKGROUND & AIMS

Maintaining endoplasmic reticulum (ER) proteostasis is essential for pancreatic acinar cell function. Under conditions of severe ER stress, activation of pathogenic unfolded protein response pathways plays a central role in the development and progression of pancreatitis. Less is known, however, of the consequence of perturbing ER-associated post-translational protein modifications on pancreatic outcomes. Here, we examined the role of the ER acetyl-CoA transporter AT-1 on pancreatic homeostasis.

METHODS

We used an AT-1S113R/+ hypomorphic mouse model, and generated an inducible, acinar-specific, AT-1 knockout mouse model, and performed histologic and biochemical analyses to probe the effect of AT-1 loss on acinar cell physiology.

RESULTS

We found that AT-1 expression is down-regulated significantly during both acute and chronic pancreatitis. Furthermore, acinar-specific deletion of AT-1 in acinar cells induces chronic ER stress marked by activation of both the spliced x-box binding protein 1 and protein kinase R-like ER kinase pathways, leading to spontaneous mild/moderate chronic pancreatitis evidenced by accumulation of intracellular trypsin, immune cell infiltration, and fibrosis. Induction of acute-on-chronic pancreatitis in the AT-1 model led to acinar cell loss and glad atrophy.

CONCLUSIONS

These results indicate a key role for AT-1 in pancreatic acinar cell homeostasis, the unfolded protein response, and that perturbations in AT-1 function leads to pancreatic disease.

All-Trans-Retinoic Acid Stimulates Overexpression of Tumor Protein D52 (TPD52, Isoform 3) and Neuronal Differentiation of IMR-32 Cells

Tumor protein D52 (TPD52), a proto-oncogene is overexpressed in a variety of epithelial carcinomas and plays an important role in cell proliferation, migration, and cell death. In the present study we found that the treatment of IMR-32 neuroblastoma (NB) cells with retinoic acid (RA) stimulates an increase in expression of TPD52. TPD52 expression is detectable after 72 h, can be maintained till differentiation of NB cells suggesting that TPD52 is involved in differentiation. Here, we demonstrate that TPD52 is essential for RA to promote differentiation of NB cells. Our results show that exogenous expression of EGFP-TPD52 in IMR-32 cells resulted cell differentiation even without RA. RA by itself and with overexpression of TPD52 can increase the ability of NB cells differentiation. Interestingly, transfection of IMR-32 cells with a specific small hairpin RNA for efficient knockdown of TPD52 attenuated RA induced NB cells differentiation. Transcriptional and translational level expression of neurotropic (BDNF, NGF, Nestin) and differentiation (β III tubulin, NSE, TH) factors in NB cells with altered TPD52 expression and/or RA treatment confirmed essential function of TPD52 in cellular differentiation. Furthermore, we show that TPD52 protects cells from apoptosis and arrest cell proliferation by varying expression of p27Kip1, activation of Akt and ERK1/2 thus promoting cell differentiation. Additionally, inhibition of STAT3 activation by its specific inhibitor arrested NB cells differentiation by EGFP-TPD52 overexpression with or without RA. Taken together, our data reveal that TPD52 act through activation of JAK/STAT signaling pathway to undertake NB cells differentiation induced by RA. J. Cell. Biochem. 118: 4358-4369, 2017. © 2017 Wiley Periodicals, Inc.

Acute acinar pancreatitis blocks vesicle-associated membrane protein 8 (VAMP8)-dependent secretion, resulting in intracellular trypsin accumulation

Zymogen secretory granules in pancreatic acinar cells express two vesicle-associated membrane proteins (VAMP), VAMP2 and -8, each controlling 50% of stimulated secretion. Analysis of secretion kinetics identified a first phase (0-2 min) mediated by VAMP2 and second (2-10 min) and third phases (10-30 min) mediated by VAMP8. Induction of acinar pancreatitis by supramaximal cholecystokinin (CCK-8) stimulation inhibits VAMP8-mediated mid- and late-phase but not VAMP2-mediated early-phase secretion. Elevation of cAMP during supramaximal CCK-8 mitigates third-phase secretory inhibition and acinar damage caused by the accumulation of prematurely activated trypsin. VAMP8^-/- acini are resistant to secretory inhibition by supramaximal CCK-8, and despite a 4.5-fold increase in total cellular trypsinogen levels, are fully protected from intracellular trypsin accumulation and acinar damage. VAMP8-mediated secretion is dependent on expression of the early endosomal proteins Rab5, D52, and EEA1. Supramaximal CCK-8 (60 min) caused a 60% reduction in the expression of D52 followed by Rab5 and EEA1 in isolated acini and in in vivo The loss of D52 occurred as a consequence of its entry into autophagic vacuoles and was blocked by lysosomal cathepsin B and L inhibition. Accordingly, adenoviral overexpression of Rab5 or D52 enhanced secretion in response to supramaximal CCK-8 and prevented accumulation of activated trypsin. These data support that acute inhibition of VAMP8-mediated secretion during pancreatitis triggers intracellular trypsin accumulation and loss of the early endosomal compartment. Maintaining anterograde endosomal trafficking during pancreatitis maintains VAMP8-dependent secretion, thereby preventing accumulation of activated trypsin.

Early to Late Endosome Trafficking Controls Secretion and Zymogen Activation in Rodent and Human Pancreatic Acinar Cells

BACKGROUND & AIMS

Pancreatic acinar cells have an expanded apical endosomal system, the physiological and pathophysiological significance of which is still emerging. Phosphatidylinositol-3,5-bisphosphate (PI(3,5)P₂) is an essential phospholipid generated by PIKfyve, which phosphorylates phosphatidylinositol-3-phosphate (PI(3)P). PI(3,5)P₂ is necessary for maturation of early endosomes (EE) to late endosomes (LE). Inhibition of EE to LE trafficking enhances anterograde endosomal trafficking and secretion at the plasma membrane by default through a recycling endosome (RE) intermediate. We assessed the effects of modulating PIKfyve activity on apical trafficking and pancreatitis responses in pancreatic acinar cells.

METHODS

Inhibition of EE to LE trafficking was achieved using pharmacological inhibitors of PIKfyve, expression of dominant negative PIKfyve K1877E, or constitutively active Rab5-GTP Q79L. Anterograde endosomal trafficking was manipulated by expression of constitutively active and dominant negative Rab11a mutants. The effects of these agents on secretion, endolysosomal exocytosis of lysosome associated membrane protein (LAMP1), and trypsinogen activation in response to high-dose CCK-8, bile acids and cigarette toxin was determined.

RESULTS

PIKfyve inhibition increased basal and stimulated secretion. Adenoviral overexpression of PIKfyve decreased secretion leading to cellular death. Expression of Rab5-GTP Q79L or Rab11a-GTP Q70L enhanced secretion. Conversely, dominant-negative Rab11a-GDP S25N reduced secretion. High-dose CCK inhibited endolysosomal exocytosis that was reversed by PIKfyve inhibition. PIKfyve inhibition blocked intracellular trypsin accumulation and cellular damage responses to high CCK-8, tobacco toxin, and bile salts in both rodent and human acini.

CONCLUSIONS

These data demonstrate that EE-LE trafficking acutely controls acinar secretion and the intracellular activation of zymogens leading to the pathogenicity of acute pancreatitis.

Tumor protein D52 (TPD52) and cancer-oncogene understudy or understudied oncogene?

The Tumor protein D52 (TPD52) gene was identified nearly 20 years ago through its overexpression in human cancer, and a substantial body of data now strongly supports TPD52 representing a gene amplification target at chromosome 8q21.13. This review updates progress toward understanding the significance of TPD52 overexpression and targeting, both in tumors known to be characterized by TPD52 overexpression/amplification, and those where TPD52 overexpression/amplification has been recently or variably reported. We highlight recent findings supporting microRNA regulation of TPD52 expression in experimental systems and describe progress toward deciphering TPD52's cellular functions, particularly in cancer cells. Finally, we provide an overview of TPD52's potential as a cancer biomarker and immunotherapeutic target. These combined studies highlight the potential value of genes such as TPD52, which are overexpressed in many cancer types, but have been relatively understudied.

Tumor protein D52 controls trafficking of an apical endolysosomal secretory pathway in pancreatic acinar cells

Zymogen granule (ZG) formation in acinar cells involves zymogen cargo sorting from trans-Golgi into immature secretory granules (ISGs). ISG maturation progresses by removal of lysosomal membrane and select content proteins, which enter endosomal intermediates prior to their apical exocytosis. Constitutive and stimulated secretion through this mechanism is termed the constitutive-like and minor-regulated pathways, respectively. However, the molecular components that control membrane trafficking within these endosomal compartments are largely unknown. We show that tumor protein D52 is highly expressed in endosomal compartments following pancreatic acinar cell stimulation and regulates apical exocytosis of an apically directed endolysosomal compartment. Secretion from the endolysosomal compartment was detected by cell-surface antigen labeling of lysosome-associated membrane protein LAMP1, which is absent from ZGs, and had incomplete overlap with surface labeling of synaptotagmin 1, a marker of ZG exocytosis. Although culturing (16-18 h) of isolated acinar cells is accompanied by a loss of secretory responsiveness, the levels of SNARE proteins necessary for ZG exocytosis were preserved. However, levels of endolysosomal proteins D52, EEA1, Rab5, and LAMP1 markedly decreased with culture. When D52 levels were restored by adenoviral delivery, the levels of these regulatory proteins and secretion of both LAMP1 (endolysosomal) and amylase was strongly enhanced. These secretory effects were absent in alanine and aspartate substitutions of serine 136, the major D52 phosphorylation site, and were inhibited by brefeldin A, which does not directly affect the ZG compartment. Our results indicate that D52 directly regulates apical endolysosomal secretion and are consistent with previous studies, suggesting that this pathway indirectly regulates ZG secretion of digestive enzymes.

A role for tumor protein TPD52 phosphorylation in endo-membrane trafficking during cytokinesis

Tumor protein D52 is expressed at high levels in exocrine cells containing large secretory granules where it regulates Ca(2+)-dependent protein secretion; however, D52 expression is also highly induced in multiple cancers. The present study investigated a role for the Ca(2+)-dependent phosphorylation of D52 at the single major phospho-acceptor site serine 136 on cell division. Ectopic expression of wild type D52 (D52wt) and the phosphomutants serine 136/alanine (S136A) or serine 136/glutamate (S136/E) resulted in significant multinucleation of cells. D52wt and S136/E each resulted in a greater than 2-fold increase in multinucleated cells compared to plasmid-transfected controls whereas the S136/A phospho-null mutant caused a 9-fold increase in multinucleation at 48h post-transfection. Electron microscopy revealed D52 expression induced a marked accumulation of vesicles along the mid-line between nuclei where the final stages of cell abscission normally occurs. Supporting this, D52wt strongly colocalized on vesicular structures containing the endosomal regulatory protein vesicle associated membrane protein 8 (VAMP 8) and this colocalization significantly increased with elevations in cellular Ca(2+). As VAMP 8 is known to be necessary for the endo-membrane fusion reactions that mediate the final stages of cytokinesis, these data indicate that D52 expression and phosphorylation at serine 136 play an important role in supporting the Ca(2+)-dependent membrane trafficking events necessary for cytokinesis in rapidly proliferating cancer cells.

MAL2 selectively regulates polymeric IgA receptor delivery from the Golgi to the plasma membrane in WIF-B cells

Myelin and lymphocyte protein 2 (MAL2) has been identified as a hepatic transcytotic regulator that mediates delivery from basolateral endosomes to the subapical compartment (SAC). However, overexpression of polymeric immunoglobulin A-receptor (pIgA-R) in polarized, hepatic WIF-B cells led to the dramatic redistribution of MAL2 into the Golgi and all the transcytotic intermediates occupied by the receptor. Although overexpressed hemagglutinin and dipeptidylpeptidase IV (DPPIV) distributed to the same compartments, MAL2 distributions did not change indicating the effect is selective. Cycloheximide treatment led to decreased pIgA-R and MAL2 intracellular staining, first in the Golgi then the SAC, suggesting they were apically delivered and that MAL2 was mediating the process. This was tested in Clone 9 cells (that lack endogenous MAL2). When expressed alone, pIgA-R was restricted to the Golgi whereas when coexpressed with MAL2, it distributed to the surface, was internalized and delivered to MAL2-positive puncta. In contrast, DPPIV distributions were independent of MAL2. Surface delivery of newly synthesized pIgA-R, but not DPPIV, was enhanced greater than ninefold by MAL2 coexpression. In WIF-B cells where MAL2 expression was knocked down, pIgA-R, but not DPPIV, was retained in the Golgi and its basolateral delivery was impaired. Thus, in addition to its role in transcytosis, MAL2 also regulates pIgA-R delivery from the Golgi to the plasma membrane.

Tumor protein D52 expression and Ca2+-dependent phosphorylation modulates lysosomal membrane protein trafficking to the plasma membrane

Tumor protein D52 (also known as CRHSP-28) is highly expressed in multiple cancers and tumor-derived cell lines; however, it is normally abundant in secretory epithelia throughout the digestive system, where it has been implicated in Ca(2+)-dependent digestive enzyme secretion (41). Here we demonstrate, using site-specific mutations, that Ca(2+)-sensitive phosphorylation at serine 136 modulates the accumulation of D52 at the plasma membrane within 2 min of cell stimulation. When expressed in Chinese hamster ovary CHO-K1 cells, D52 colocalized with adaptor protein AP-3, Rab27A, vesicle-associated membrane protein VAMP7, and lysosomal-associated membrane protein LAMP1, all of which are present in lysosome-like secretory organelles. Overexpression of D52 resulted in a marked accumulation of LAMP1 on the plasma membrane that was further enhanced following elevation of cellular Ca(2+). Strikingly, mutation of serine 136 to alanine abolished the Ca(2+)-stimulated accumulation of LAMP1 at the plasma membrane whereas phosphomimetic mutants constitutively induced LAMP1 plasma membrane accumulation independent of elevated Ca(2+). Identical results were obtained for endogenous D52 in normal rat kidney and HeLA cells, where both LAMP1 and D52 rapidly accumulated on the plasma membrane in response to elevated cellular Ca(2+). Finally, D52 induced the uptake of LAMP1 antibodies from the cell surface in accordance with both the level of D52 expression and phosphorylation at serine 136 demonstrating that D52 altered the plasma membrane recycling of LAMP1-associated secretory vesicles. These findings implicate both D52 expression and Ca(2+)-dependent phosphorylation at serine 136 in lysosomal membrane trafficking to and from the plasma membrane providing a novel Ca(2+)-sensitive pathway modulating the lysosome-like secretory pathway.

Altered expression of tumor protein D52 regulates apoptosis and migration of prostate cancer cells

Tumor protein D52 (TPD52) is a protein found to be overexpressed in prostate and breast cancer due to gene amplification. However, its physiological function remains under investigation. In the present study, we investigated the response of the LNCaP human prostate carcinoma cell line to deregulation of TPD52 expression. Proteomic analysis of prostate biopsies showed TPD52 overexpression at the protein level, whereas its transcriptional upregulation was demonstrated by real-time PCR. Transfection of LNCaP cells with a specific small hairpin RNA giving efficient knockdown of TPD52 resulted in significant cell death of the carcinoma LNCaP cells. As demonstrated by activation of caspases (caspase-3 and -9), and by the loss of mitochondrial membrane potential, cell death occurs due to apoptosis. The disruption of the mitochondrial membrane potential indicates that TPD52 acts upstream of the mitochondrial apoptotic reaction. To study the effect of TPD52 expression on cell proliferation, LNCaP cells were either transfected with enhanced green fluorescence protein-TPD52 or a specific small hairpin RNA. Enhanced green fluorescence protein-TPD52 overexpressing cells showed an increased proliferation rate, whereas TPD52-depleted cells showed the reverse effect. Additionally, we demonstrate that exogenous expression of TPD52 promotes cell migration via alphav beta3 integrin in prostate cancer cells through activation of the protein kinase B/Akt signaling pathway. From these results, we conclude that TPD52 plays an important role in various molecular events, particularly in the morphological diversification and dissemination of prostate carcinoma cells, and may be a promising target with respect to developing new therapeutic strategies to treat prostate cancer.

Calcium/calmodulin-dependent phosphorylation of tumor protein D52 on serine residue 136 may be mediated by CAMK2delta6

Tumor protein D52 is expressed at relatively high levels in cells within the gastrointestinal tract that undergo classical exocytosis and is overexpressed in several cancers. Current evidence supports a role for D52 in the regulation of vesicular trafficking. D52 function(s) are regulated by calcium-dependent phosphorylation; however, the intracellular mechanisms that mediate this process are not well characterized. The goal of this study was to identify the calcium-dependent phosphorylation site(s) in D52 and to characterize the protein kinase(s) that mediate this phosphorylation. Using mass spectrometry and site-directed mutagenesis, we identified a single amino acid residue, S(136), that undergoes increased phosphorylation upon elevation of intracellular Ca(2+) concentration. A phosphospecific antibody (pS(136)) was produced and used to characterize D52 kinase activity in gastric mucosal, colonic T84, and HEK293 cells. By using D52 as a substrate, a protein kinase with a molecular weight (M(r)) of approximately 50 kDa was identified with "in gel" assays. This kinase comigrated with rat brain calcium/calmodulin-dependent protein kinase (CAMK2)alpha cross-reacted with pan-specific CAMK2 antibodies as well as with anti-active CAMK2 (pT(286/287)) antibody when activated. Carbachol-stimulated phosphorylation of S(136) was inhibited by the CAMK2 inhibitor KN93 (IC(50) 38 microM) and by the calmodulin antagonist W7 (IC(50) 3.3 nM). A previously uncharacterized CAMK2 isoform, CAMK2delta6, which has the same domain structure and M(r) as CAM2alpha, was identified in gastric mucosa by RT-PCR. The cloned, expressed protein comigrated with D52 kinase and colocalized with D52 protein in T84 and HEK293 cells. These findings support a role for CAMK2delta6 in the mediation of D52 phosphorylation.

A testis-specific and testis developmentally regulated tumor protein D52 (TPD52)-like protein TPD52L3/hD55 interacts with TPD52 family proteins

Tumor protein D52-like proteins (TPD52) are small coiled-coil motif bearing proteins that were first identified in breast cancer. TPD52 and related proteins have been implicated in cell proliferation, apoptosis, and vesicle trafficking. To date, three human TPD52 members had been identified, named hD52 (TPD52), hD53 (TPD52L1), and hD54 (TPD52L2). The most important characteristic of the protein family is a highly conserved coiled-coil motif that is required for homo- and heteromeric interaction with other TPD52-like proteins. Herein, we identified a novel TPD52-like sequence (TPD52L3, or hD55) in human testis using cDNA microarray. Sequence analysis of the deduced protein suggests that hD55 contains a coiled-coil motif and is highly conserved compared with other TPD52-like sequences. Yeast two-hybrid and GST pull-down assays revealed that hD55 interacts with hD52, hD53, hD54, and itself. cDNA microarray detection found that hD55 was expressed at 5.6-fold higher levels in adult testis than in fetal testis. Additionally, the expression profile shows that hD55 is testis-specific, indicating a potential role for hD55 in testis development and spermatogenesis.

The tumor protein D52 family: many pieces, many puzzles

Tumor protein D52-like proteins are small coiled-coil motif bearing proteins which are conserved from lower organisms to human. The founding member of the family, human D52, has principally attracted research interest due to its frequent overexpression in cancer, often in association with D52 gene amplification. This review summarises published literature concerning this protein family since their discovery, which is highlighting an increasing diversity of functions for D52-like proteins. This in turn highlights a need for more comparative functional analyses, to determine which functions are conserved and which may be isoform-specific. This knowledge will be crucial for any future manipulation of D52 function in human disease, including cancer.

Secretagogue-induced translocation of CRHSP-28 within an early apical endosomal compartment in acinar cells

Ca(2+)-regulated heat-stable protein (CRHSP-28) is a member of the TPD52 protein family that has been shown to regulate Ca(2+)-dependent secretory activity in pancreatic acinar cells. Immunofluorescence microscopy of isolated lobules demonstrated that CRHSP-28 is localized to a supranuclear apical compartment in acini and accumulates immediately below the apical membrane within 2 min of CCK octapeptide (CCK-8) stimulation. Dual-immunofluorescence microscopy demonstrated an endosomal localization of CRHSP-28 that strongly overlapped with early endosomal antigen-1 (EEA-1) on vesicular structures throughout the apical cytoplasm but showed only minimal overlap with the transferrin receptor, which is present in basolaterally derived endosomes. Significant overlapping of CRHSP-28 with the trans-Golgi network marker-38 was also noted in supranuclear regions of acini. Interestingly, treatment of lobules with brefeldin A reversibly disrupted the vesicular localization of CRHSP-28 and EEA-1 within the apical cytoplasm. The CCK-8-induced accumulation of CRHSP-28 in subapical regions of acini was not altered by inhibition of apical endocytosis with the actin filament-disrupting agent latrunculin B. Immunoelectron microscopy confirmed that CRHSP-28 is associated with the limiting membrane of irregularly shaped vesicular structures of low electron density in the apical cytoplasm that are positive for EEA-1 staining. Sparse, but significant, CRHSP-28 immunoreactivity was also observed along the limiting membrane of zymogen granules. Consistent with immunofluorescence data, CRHSP-28 was found to accumulate in clusters on endosomes and positioned between zymogen granules below the cell apex on CCK-8 stimulation. These data indicate that CRHSP-28 is present within endocytic and exocytic compartments of acinar cells and is acutely regulated by secretagogue stimulation.

Positive regulation of apoptosis signal-regulating kinase 1 by hD53L1

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase family member that plays a central role in cytokine- and stress-induced apoptosis by activating c-Jun N-terminal kinase and p38 signaling cascades. ASK1-induced apoptotic activity is up-regulated by two cellular factors, Daxx and TRAF2, through direct protein-protein interactions. Daxx and TRAF2 are death receptor-associated proteins in Fas and tumor necrosis factor-alpha pathways, respectively. Recent studies suggest that calcium signaling may regulate ASK1 pathway. Here we report that human D53L1, a member of the tumor protein D52 family involved in cell proliferation and calcium signaling, up-regulates the ASK1-induced apoptosis. The human D53L1 physically interacts with the C-terminal regulatory domain of ASK1 and promotes ASK1-induced apoptotic activity by activating caspase signaling in mammalian cells. In luciferase reporter assays, hD53L1 activates c-Jun N-terminal kinase-mediated transactivation in the presence of ASK1. Expression of hD53L1 enhances autophosphorylation and kinase activity of ASK1 but has no effect on ASK1 oligomerization that is necessary for kinase activity and on binding of ASK1 to MKK6, a downstream factor of ASK1. Taken together, these results suggest that activation of ASK1 by hD53L1 may provide a novel mechanism for ASK1 regulation.