PAP IB, a new member of the Reg gene family: cloning, expression, structural properties, and evolution by gene duplication

Identification of regenerating island-derived protein 3E in dogs

Regenerating islet-derived protein (REG) 1A (aka pancreatic stone protein) and REG3A (aka pancreatitis-associated protein) are upregulated in humans with sepsis, pancreatitis, and gastrointestinal diseases, but little is known about this protein family in dogs. Our aim was to identify REG1 and REG3 family members in dogs. REG-family genes were computationally annotated in the canine genome and proteome, with verification of gene expression using publicly available RNA-seq data. The presence of the protein in canine pancreatic tissue and plasma was investigated with Western blot and immunohistochemistry, using anti-human REG1A and REG3A antibodies. Protein identity was confirmed with mass spectrometry. Two members of the REG3 subfamily were found in the canine genome, REG3E1 and REG3E2, both encoding for the same 176 AA protein, subsequently named REG3E. Anti-human REG3A antibodies demonstrated cross-reactivity with the canine REG3E protein in pancreas homogenates. In canine plasma, a protein band of approximately 17 kDa was apparent. Mass spectrometry confirmed this protein to be the product of the two annotated REG3E genes. Strong immunoreactivity to anti-human REG3A antibodies was found in sections of canine pancreas affected with acute pancreatitis, but it was weak in healthy pancreatic tissue. Recombinant canine REG3E protein underwent a selective trypsin digestion as described in other species. No evidence for the presence of a homolog of REG1A in dogs was found in any of the investigations. In conclusion, dogs express REG3E in the pancreas, whose role as biomarker merits further investigations. Homologs to human REG1A are not likely to exist in dogs.

The regenerating protein 3A: a crucial molecular with dual roles in cancer

Introduction

REG3A, a member of the third subclass of the Reg family, has been found in a variety of tissues but is not detected in immune cells. In the past decade, it has been determined that REG3A expression is regulated by injury, infection, inflammatory stimuli, and pro-cytokines via different signaling pathways, and it acts as a tissue-repair, bactericidal, and anti-inflammatory molecule in human diseases. Recently, the role of REG3A in cancer has received increasing attention. The present article aims to investigate the structure, expression, regulation, function of REG3A, and to highlight the potential role of REG3A in tumors.

Methods

A detailed literature search and data organization were conducted to find information about the role of REG3A in variety of physiological functions and tumors.

Results

Contradictory roles of REG3A have been reported in different tumor models. Some studies have demonstrated that high expression of REG3A in cancers can be oncogenic. Other studies have shown decreased REG3A expression in cancer cells as well as suppressed tumor growth.

Conclusions

Taken together, better understanding of REG3A may lead to new insights that make it a potentially useful target for cancer therapy.

Reg-1α Promotes Differentiation of Cortical Progenitors via Its N-Terminal Active Domain

Reg-1α belongs to the Reg family of small, secreted proteins expressed in both pancreas and nervous system. Reg-1α is composed of two domains, an insoluble C-type lectin domain and a short soluble N-terminal peptide, which is released from the molecule upon proteolytic N-terminal processing, although the biological significance of this proteolysis remains unclear. We have previously shown that binding of Reg-1α to its receptor Extl3 stimulates axonal outgrowth. Reg-1α and Extl3 genes are expressed in the developing cortex but their expression decreases in adulthood, pointing to a possible function of this signaling system at the early developmental stages. Here, we demonstrate that recombinant Reg-1α increases migration and differentiation of cultured embryonic rat telencephalic progenitors via the activation of GSK-3β activity. In vivo overexpression of Reg-1α by in utero electroporation, has a similar effect, favoring premature differentiation of cortical progenitors. Notably, the N-terminal soluble domain, but not the C-type lectin domain, is largely responsible for Reg-1α effects on cortical neuronal differentiation. We thus conclude that Reg-1α via its proteolytically generated N-terminal domain is required for basic development processes.

Effects of Reg3 Delta Bioactive Peptide on Blood Glucose Levels and Pancreatic Gene Expression in an Alloxan-Induced Mouse Model of Diabetes

OBJECTIVE

The endocrine regeneration of the pancreas holds great potential for stable diabetes therapy. The Regeneration (Reg) family of proteins has been associated with pancreas regeneration. Hence, the Reg3 delta bioactive peptide from a mouse was evaluated to see whether it can reverse hyperglycemia in a mouse model of diabetes with any effects on pancreatic gene expression.

METHODS

In this study, we administrated the synthetic Reg3 delta bioactive peptide to healthy mice and to alloxan-induced mouse models of diabetes for 30 days, with weekly measurements of body weight and blood glucose levels. After 1 month, pancreatic gene profiling of these mice was performed for the Ngn-3, Pdx-1, MapK8, IGF-1, IGF2bp2, Reg3 beta and Reg3 delta genes.

RESULTS

The glycemic levels in mice with diabetes were decreased significantly, restored almost to normal. Furthermore, the gene expression levels measured by quantitative polymerase chain reaction (qPCR) showed that messenger RNA (mRNA) levels of 2 important transcription factors (Ngn-3 and Pdx-1) were increased during the Reg3 delta peptide treatment.

CONCLUSIONS

This study shows that Reg3 delta has the potential to reverse hyperglycemia by modulating gene expression in pancreatic endocrine precursor markers Pdx-1 and Ngn-3, which require further investigation at the protein and immunohistology levels.

Defining the Interaction of Human Soluble Lectin ZG16p and Mycobacterial Phosphatidylinositol Mannosides

ZG16p is a soluble mammalian lectin that interacts with mannose and heparan sulfate. Here we describe detailed analysis of the interaction of human ZG16p with mycobacterial phosphatidylinositol mannosides (PIMs) by glycan microarray and NMR. Pathogen-related glycan microarray analysis identified phosphatidylinositol mono- and di-mannosides (PIM1 and PIM2) as novel ligand candidates of ZG16p. Saturation transfer difference (STD) NMR and transferred NOE experiments with chemically synthesized PIM glycans indicate that PIMs preferentially interact with ZG16p by using the mannose residues. The binding site of PIM was identified by chemical-shift perturbation experiments with uniformly (15)N-labeled ZG16p. NMR results with docking simulations suggest a binding mode of ZG16p and PIM glycan; this will help to elucidate the physiological role of ZG16p.

Overexpression of REG4 confers an independent negative prognosticator in rectal cancers receiving concurrent chemoradiotherapy

BACKGROUND AND OBJECTIVES

Neoadjuvant concurrent chemoradiotherapy (CCRT) followed by surgery is the standard treatment for locally advanced rectal cancer. Through data mining from published transcriptomic database, we identified Regenerating Gene Type IV (REG4) as the most significantly associated gene with resistance to CCRT. This study examined the prognostic impact of REG4 expression in patients with rectal cancer receiving neoadjuvant CCRT.

METHODS

REG4 immunohistochemistry was retrospectively assessed for pre-treatment biopsy specimens from 172 rectal cancer patients who received neoadjuvant CCRT followed by surgery without initial distant metastasis. The results were correlated with the clinicopathological variables, disease-specific survival (DSS), local recurrence-free survival (LRFS), and distant metastasis-free survival (DMFS), as well as γ-H2AX expression in post-treatment tumor samples.

RESULTS

High expression of REG4 was associated with advanced pre-treatment nodal status (P = 0.026), advanced post-treatment tumor status (P = 0.006), advanced post-treatment nodal status (P = 0.001), advanced post-treatment tumor stage (P < 0.001), and inferior tumor regression grade (P = 0.001). Of note, high expression of REG4 emerged as an adverse prognosticator for DSS (P = 0.0004), LRFS (P = 0.0009), and MeFS (P = 0.0254). After multivariate comparisons, it remained independently prognostic for worse DSS (hazard ratio [HR] = 2.731; P = 0.025) and LRFS (HR = 2.676; P = 0.029). High expression of REG4 was also negatively associated with γ-H2AX expression (P < 0.0001, r = -0.708).

CONCLUSIONS

High expression of REG4 is associated with poor therapeutic response, adverse outcome and an aggressive phenotype in rectal cancer patients treated with neoadjuvant CCRT, justifying REG4 is a surrogate marker to predict CCRT resistance.

Reg4-induced mitogenesis involves Akt-GSK3β-β-Catenin-TCF-4 signaling in human colorectal cancer

Upregulation of regenerating gene 4 (Reg4) is observed in many human gastrointestinal malignancies including colorectal cancer (CRC). We previously reported a Reg4-mediated induction of epidermal growth factor receptor-Akt-AP1 signaling regulating CRC cell apoptosis. However, the role of Reg4 in the regulation of CRC cell division is poorly understood. This study tests the hypothesis that Reg4 induces Akt-GSK3β-β-Catenin-TCF-4 signaling to regulate CRC cell division. In vitro models of human CRC were used to determine the role of Reg4 in regulation of CRC cell division. Cell cycle studies demonstrated that Reg4 treatment significantly decreased CRC cell number in G1 phase and increased in G2 phase. Subsequently Reg4 significantly increased the mitotic index of CRC cells. As assessed by real-time RT-PCR and Western blot analyses, Reg4 significantly increased the expression of cell cycle regulatory genes Cyclin D1 and D3, and associated Cyclin-dependent kinases (CDK4 and CDK6). Reg4-mediated increase in these genes involved a pathway that included an induced Akt activity by increasing phosphorylation of Thr308 and Ser473, a reduced glycogen synthase kinase 3β (GSK-3β) activity by increasing phosphorylation of Ser9, an induced nuclear translocation of β-Catenin by decreasing phosphorylation of Ser33/37/Thr41, and an increased TCF-4 transcriptional activity. Furthermore, antagonism of Reg4-signaling using Reg4-specific mAbs (2H6 and 3E5) and Akt inhibitor significantly decreased, whereas agonism using GSK-3β antagonist (SB216763) significantly increased mitotic index and proliferation of CRC cells. These results identify Reg4 as a key regulator of the CRC cell division and proliferation, hence a potential target of human CRC treatment.

Regenerating islet-derived 1α (Reg-1α) protein is new neuronal secreted factor that stimulates neurite outgrowth via exostosin Tumor-like 3 (EXTL3) receptor

Regenerating islet-derived 1α (Reg-1α)/lithostathine, a member of a family of secreted proteins containing a C-type lectin domain, is expressed in various organs and plays a role in proliferation, differentiation, inflammation, and carcinogenesis of cells of the digestive system. We previously reported that Reg-1α is overexpressed during the very early stages of Alzheimer disease, and Reg-1α deposits were detected in the brain of patients with Alzheimer disease. However, the physiological function of Reg-1α in neural cells remains unknown. Here, we show that Reg-1α is expressed in neuronal cell lines (PC12 and Neuro-2a) and in rat primary hippocampal neurons (E17.5). Reg-1α is mainly localized around the nucleus and at the membrane of cell bodies and neurites. Transient overexpression of Reg-1α or addition of recombinant Reg-1α significantly increases the number of cells with longer neurites by stimulating neurite outgrowth. These effects are abolished upon down-regulation of Reg-1α by siRNA and following inhibition of secreted Reg-1α by antibodies. Moreover, Reg-1α colocalizes with exostosin tumor-like 3 (EXTL3), its putative receptor, at the membrane of these cells. Overexpression of EXTL3 increases the effect of recombinant Reg-1α on neurite outgrowth, and Reg-1α is not effective when EXTL3 overexpression is down-regulated by shRNA. Our findings indicate that Reg-1α regulates neurite outgrowth and suggest that this effect is mediated by its receptor EXTL3.

Regenerating proteins and their expression, regulation and signaling

The regenerating (Reg) protein family comprises C-type lectin-like proteins discovered independently during pancreatitis and pancreatic islet regeneration. However, an increasing number of studies provide evidence of participation of Reg proteins in the proliferation and differentiation of diverse cell types. Moreover, Reg family members are associated with various pathologies, including diabetes and forms of gastrointestinal cancer. These findings have led to the emergence of key roles for Reg proteins as anti-inflammatory, antiapoptotic and mitogenic agents in multiple physiologic and disease contexts. Yet, there are significant gaps in our knowledge regarding the regulation of expression of different Reg genes. In addition, the pathways relaying Reg-triggered signals, their targets and potential cross-talk with other cascades are still largely unknown. In this review, the expression patterns of different Reg members in the pancreas and extrapancreatic tissues are described. Moreover, factors known to modulate Reg levels in different cell types are discussed. Several signaling pathways, which have been implicated in conferring the effects of Reg ligands to date, are also delineated. Further efforts are necessary for elucidating the biological processes underlying the action of Reg proteins and their involvement in various maladies. Better understanding of the function of Reg genes and proteins will be beneficial in the design and development of therapies utilizing or targeting this protein group.

Reg IV regulates normal intestinal and colorectal cancer cell susceptibility to radiation-induced apoptosis

BACKGROUND & AIMS

Regenerating (Reg) gene IV is predominantly expressed in gastrointestinal cells and highly up-regulated in many gastrointestinal malignancies, including colorectal cancer (CRC). Human CRC cells expressing higher levels of Reg IV gene and its protein product (Reg IV) are resistant to conventional therapies, including irradiation (IR). However, the underlying mechanism is not well defined.

METHODS

A murine model of IR-induced intestinal injury and in vitro and in vivo models of human CRC were used to determine the role of Reg IV in regulation of normal intestinal and colorectal cancer cell susceptibility to IR-induced apoptosis.

RESULTS

Treatments of recombinant human Reg IV (rhR4) protein protected normal intestinal crypt cells from IR-induced apoptosis by increasing the expression of antiapoptotic genes Bcl-2, Bcl-XL, and survivin. However, overexpression of Reg IV in human CRC cells was associated with increased resistance to IR-induced apoptosis. Therefore, we used antagonism of Reg IV as a tool to increase CRC cell susceptibility to IR-induced cell death. Two complementary approaches using specific monoclonal antibodies and small interfering RNAs were tested in both in vitro and in vivo models of human CRC. Both approaches resulted in increased apoptosis and decreased cell proliferation, leading to decreased tumor growth and increased animal survival. Furthermore, these approaches increased CRC cell susceptibility to IR-induced apoptosis.

CONCLUSIONS

These results implicate Reg IV as an important modulator of gastrointestinal cell susceptibility to IR; hence, it is a potential target for adjunctive treatments for human CRC and other gastrointestinal malignancies.

Overexpression of Reg3alpha increases cell growth and the levels of cyclin D1 and CDK4 in insulinoma cells

Regenerating gene (Reg) family protein Reg3alpha is normally expressed in pancreatic acinar and endocrine cells. In order to explore its effect on islet beta-cell replication, insulinoma MIN6 cells were stably transfected with murine Reg3alpha cDNA. Determined using real-time PCR and Western blots, the levels of Reg3alpha mRNA and protein in Reg3alpha-transfected clones were increased 10- and 6-fold, respectively. Western blots also revealed that the protein was released into the culture medium, consistent with an endocrine effect. In MTT cell proliferation assay, Reg3alpha-overexpressing cells exhibited a 2-fold increase in the rate of cell growth. In order to investigate the intracellular mechanism, we studied cell cycle regulatory proteins. In Reg3alpha-expressing cells, we detected 2.2- and 2.5-fold increased levels of cyclin D1 and CDK4, respectively, which paralleled a 1.8-fold increase in the rate of Akt phosphorylation. It is established that beta-cell replication is associated with increased cyclin D1 and CDK4 levels; deficiency in CDK4 or cyclin D2 results in reduced beta-cell mass and diabetes. Our results suggest that Reg3alpha stimulates beta-cell replication, by activating Akt kinase and increasing the levels of cyclin D1/CDK4.

Does IGF-I stimulate pancreatic islet cell growth?

Both IGF-I and its receptor (IGF-IR) are specifically expressed in various cell types of the endocrine pancreas. IGF-I has long been considered a growth factor for islet cells as it induces DNA synthesis in a glucose-dependent manner, prevents Fas-mediated autoimmune beta-cell destruction and delays onset of diabetes in non-obese diabetic (NOD) mice. Islet-specific IGF-I overexpression promotes islet cell regeneration in diabetic mice. However, in the last few years, results from most gene-targeted mice have challenged this view. For instance, combined inactivation of insulin receptor and IGF-IR or IGF-I and IGF-II genes in early embryos results in no defect on islet cell development; islet beta-cell-specific inactivation of IGF-IR gene causes no change in beta-cell mass; liver- and pancreatic-specific IGF-I gene deficiency (LID and PID mice) suggests that IGF-I exerts an inhibitory effect on islet cell growth albeit indirectly through controlling growth hormone release or expression of Reg family genes. These results need to be evaluated with potential gene redundancy, model limitations, indirect effects and ligand-receptor cross-activations within the insulin/IGF family. Although IGF-I causes islet beta-cell proliferation and neogenesis directly, what occur in normal physiology, pathophysiology or during development of an organism might be different. Locally produced and systemic IGF-I does not seem to play a positive role in islet cell growth. Rather, it is probably a negative regulator through controlling growth hormone and insulin release, hyperglycemia, or Reg gene expression. These results complicate the perspective of an IGF-I therapy for beta-cell loss.

The identification and sequence analysis of a new Reg3gamma and Reg2 in the Syrian golden hamster

The regenerating (Reg) genes are associated with tissue repair and have been directly implicated in pancreatic beta-cell regeneration. A hamster Reg3, Islet neogenesis associated protein (INGAP), has been shown to possess anti-diabetic properties in rodent models. Although several Reg3 proteins have been identified in other species, INGAP is the only Reg3 found in hamsters. To identify new Reg3 genes in the hamster pancreas we employed homology reverse transcription polymerase chain reaction (RT-PCR) using degenerate Reg3 primers, followed by rapid amplification of cDNA ends (RACE). We report here the discovery of a new hamster Reg3 gene of 765 nucleotides (nt) that encodes a 174-amino acid (aa) protein. This protein sequence was identified as a novel hamster Reg3gamma with 78% and 75% identity to the rat Reg3gamma and mouse Reg3gamma protein, respectively. We also fully sequenced the previously reported partial sequence of the hamster Reg1 gene coding region using RACE to yield a 756-nt transcript that encodes a deduced 173 aa protein. This protein was identified as hamster Reg2, rather than Reg1 as was initially reported, with an 81% identity to mouse Reg2. The spatial gene expression patterns of the hamster Reg genes, analyzed by RT-PCR, were similarly distributed with low level expression being found globally throughout the body. Mice and hamsters are the only species known to carry either of the functional INGAP or Reg2 genes. It remains to be determined whether these genes bestow mice and hamsters with special regenerative abilities in the pancreas.

The role of Islet Neogenesis-Associated Protein (INGAP) in islet neogenesis

Islet Neogenesis-Associated Protein (INGAP) is a member of the Reg family of proteins implicated in various settings of endogenous pancreatic regeneration. The expression of INGAP and other RegIII proteins has also been linked temporally and spatially with the induction of islet neogenesis in animal models of disease and regeneration. Furthermore, administration of a peptide fragment of INGAP (INGAP peptide) has been demonstrated to reverse chemically induced diabetes as well as improve glycemic control and survival in an animal model of type 1 diabetes. Cultured human pancreatic tissue has also been shown to be responsive to INGAP peptide, producing islet-like structures with function, architecture and gene expression matching that of freshly isolated islets. Likewise, studies in normoglycemic animals show evidence of islet neogenesis. Finally, recent clinical studies suggest an effect of INGAP peptide to improve insulin production in type 1 diabetes and glycemic control in type 2 diabetes.

Prospects and challenges for islet regeneration as a treatment for diabetes: a review of islet neogenesis associated protein

Diabetes mellitus results from inadequate insulin action, which can be viewed as a consequence of the limited ability to restore beta cells after they are lost as the result of metabolic exhaustion, autoimmune destruction, or surgical insult. Arguably, a uniformly effective therapeutic pathway to address all forms of diabetes would be to reverse the restrictions on beta-cell and islet regeneration. The development from progenitor cells of islets with normal endocrine function does occur in adult humans; it is referred to as islet neogenesis. The induction of islet neogenesis is an important, if not essential, therapeutic approach for curing type 1 diabetes mellitus (T1DM) and could be valuable in the treatment of type 2 diabetes mellitus (T2DM) as well. Islet neogenesis associated protein (INGAP) is the first therapeutic candidate to be identified as the result of a purposeful search for an endogenous molecule with islet neogenic activity. It was found that partial obstruction of the pancreatic duct in hamsters induced islet neogenesis; under this condition, a neogenesis-promoting activity was identified and partially purified from a soluble tissue fraction. A 168-kDa protein product of the cloned gene was found to be responsible for the neogenesis activity. This molecule named INGAP contains an active core sequence of amino acids called INGAP peptide. Results from in vitro, animal, and human studies suggest that INGAP and INGAP peptide are neogenic in at least several vertebrate species, including humans. INGAP has since been found to be a member of the family of Reg proteins, which are found across and in multiple versions within species and are closely associated with embryonic and regenerative processes. Clinical results suggest that INGAP peptide can be a suitable neogenesis therapy, but optimization of the therapy and more data are required to fully access this potential. Understanding of the signaling pathways of INGAP and other related Reg proteins is a promising means of advancing therapeutic development for people with T1DM and T2DM. The quest for the fundamental restorative approach to lost insulin secretion is an enticing target for drug development.

STAT3 activation regulates growth, inflammation, and vascularization in a mouse model of gastric tumorigenesis

BACKGROUND & AIMS

The gp130(757F/F) mouse is a well-characterized and robust model of distal gastric tumorigenesis displaying many of the characteristics of human intestinal type gastric cancer. Key to the development of tumors in this model, and in many examples of human tumor development, is hyperactivation of the transcription factor STAT3. This study addressed the requirement for STAT3 activation in tumor initiation and characterized some of the genes downstream of STAT3 required for tumor development. Furthermore, the interaction among STAT3, the microbial environment, and tumorigenesis was evaluated.

METHODS

The role of STAT3 in gastric tumor development was assessed in detail in gp130(757F/Y757F):STAT3(+/-) mice displaying reduced STAT3 activity. Tumor size was quantified morphologically, and the effects on endocrine cell populations, neovascularization, and inflammatory cell infiltration as well as the outcome of STAT3 activation on transcription of a number of genes relevant in growth and inflammation were quantified.

RESULTS

Loss of one STAT3 allele in gp130(757F/F) mice reduced the frequency and rate of tumor development because of inhibition of proliferation-induced glandular hyperplasia. There was also a concomitant reduction in the degree of inflammatory infiltration and cytokine and chemokine expression, angiogenesis, and expression of metalloproteinases and growth factors. Antimicrobial treatment of gp130(757F/F) mice slowed tumor growth coincident with reduced macrophage and neutrophil infiltration.

CONCLUSIONS

Activation of STAT3 and the microbial environment are pivotal for gastric tumor initiation and development in the gp130(757F/F) mouse, thus supporting the notion that STAT3 activation may play a role in human gastric cancer development.

Activation of the Reg family genes by pancreatic-specific IGF-I gene deficiency and after streptozotocin-induced diabetes in mouse pancreas

We have recently reported that Pdx1-Cre-mediated whole pancreas inactivation of IGF-I gene [in pancreatic-specific IGF-I gene-deficient (PID) mice] results in increased beta-cell mass and significant protection against both type 1 and type 2 diabetes. Because the phenotype is unlikely a direct consequence of IGF-I deficiency, the present study was designed to explore possible activation of proislet factors in PID mice by using a whole genome DNA microarray. As a result, multiple members of the Reg family genes (Reg2, -3alpha, and -3beta, previously not known to promote islet cell growth) were significantly upregulated in the pancreas. This finding was subsequently confirmed by Northern blot and/or real-time PCR, which exhibited 2- to 8-fold increases in the levels of these mRNAs. Interestingly, these Reg family genes were also activated after streptozotocin-induced beta-cell damage and diabetes (wild-type T1D mice) when islet cells were undergoing regeneration. Immunohistochemistry revealed increased Reg proteins in exocrine as well as endocrine pancreas and suggested their potential role in beta-cell neogenesis in PID or T1D mice. Previously, other Reg proteins (Reg1 and islet neogenesis-associated protein) have been shown to promote islet cell replication and neogenesis. These uncharacterized Reg proteins may play a similar but more potent role, not only in normal islet cell growth in PID mice, but also in islet cell regeneration after T1D.