An IRBIT homologue lacks binding activity to inositol 1,4,5-trisphosphate receptor due to the unique N-terminal appendage

NRAS Mutant Dictates AHCYL1-Governed ER Calcium Homeostasis for Melanoma Tumor Growth

Calcium homeostasis is critical for cell proliferation, and emerging evidence shows that cancer cells exhibit altered calcium signals to fulfill their need for proliferation. However, it remains unclear whether there are oncogene-specific calcium homeostasis regulations that can expose novel therapeutic targets. Here, from RNAi screen, we report that adenosylhomocysteinase like protein 1 (AHCYL1), a suppressor of the endoplasmic reticulum (ER) calcium channel protein inositol trisphosphate receptor (IP3R), is selectively upregulated and critical for cell proliferation and tumor growth potential of human NRAS-mutated melanoma, but not for melanoma expressing BRAF V600E. Mechanistically, AHCYL1 deficiency results in decreased ER calcium levels, activates the unfolded protein response (UPR), and triggers downstream apoptosis. In addition, we show that AHCYL1 transcription is regulated by activating transcription factor 2 (ATF2) in NRAS-mutated melanoma. Our work provides evidence for oncogene-specific calcium regulations and suggests AHCYL1 as a novel therapeutic target for RAS mutant-expressing human cancers, including melanoma.

IMPLICATIONS

Our findings suggest that targeting the AHCYL1-IP3R axis presents a novel therapeutic approach for NRAS-mutated melanomas, with potential applicability to all cancers harboring RAS mutations, such as KRAS-mutated human colorectal cancers.

Identification of cuproptosis-related molecular classification and characteristic genes in ulcerative colitis

Ulcerative colitis (UC) is a refractory inflammatory disease with imbalances in intestinal mucosal homeostasis. Cuproptosis serves as newly identified programmed cell death (PCD) form involved in UC. In the study, UC-related datasets were extracted from the Gene Expression Omnibus (GEO) database. A comparison of UC patients and healthy controls identified 11 differentially expressed cuproptosis-related genes (DE-CRGs), where FDX1, LIAS, and DLAT were differentially expressed in UC groups from the mouse models and clinical samples, with their expression correlating with disease severity. By comprehending weighted gene co-expression network analysis (WGCNA) and differential expression analysis, the key genes common to the module genes relevant to different cuproptosis-related clusters and differentially expressed genes (DEGs) both in different clusters and patients with and without UC were identified using several bioinformatic analysis. Furthermore, the mRNA levels of four characteristic genes with diagnostic potential demonstrated significant decrease in both mouse models and clinical UC samples. Our discoveries offer a theoretical foundation for cuproptosis effect in UC.

Both IRBIT and long-IRBIT bind to and coordinately regulate Cl-/HCO3- exchanger AE2 activity through modulating the lysosomal degradation of AE2

Anion exchanger 2 (AE2) plays crucial roles in regulating cell volume homeostasis and cell migration. We found that both IRBIT and Long-IRBIT (L-IRBIT) interact with anion exchanger 2 (AE2). The interaction occurred between the conserved AHCY-homologous domain of IRBIT/L-IRBIT and the N-terminal cytoplasmic region of AE2. Interestingly, AE2 activity was reduced in L-IRBIT KO cells, but not in IRBIT KO cells. Moreover, AE2 activity was slightly increased in IRBIT/L-IRBIT double KO cells. These changes in AE2 activity resulted from changes in the AE2 expression level of each mutant cell, and affected the regulatory volume increase and cell migration. The activity and expression level of AE2 in IRBIT/L-IRBIT double KO cells were downregulated if IRBIT, but not L-IRBIT, was expressed again in the cells, and the downregulation was cancelled by the co-expression of L-IRBIT. The mRNA levels of AE2 in each KO cell did not change, and the downregulation of AE2 in L-IRBIT KO cells was inhibited by bafilomycin A1. These results indicate that IRBIT binding facilitates the lysosomal degradation of AE2, which is inhibited by coexisting L-IRBIT, suggesting a novel regulatory mode of AE2 activity through the binding of two homologous proteins with opposing functions.

TMT proteomics analysis of intestinal tissue from patients of irritable bowel syndrome with diarrhea: Implications for multiple nutrient ingestion abnormality

Diarrheal irritable bowel syndrome (IBS-D) is a chronic functional bowel disease with no clear diagnostic markers and no satisfactory treatment strategies. In recent years, the importance of intestinal microstructure and function in IBS-D has been emphasized. However, the intestinal tissue proteomics of IBS-D patients has not been analyzed. Here, we systematically analyzed the molecule profiling of the intestinal tissues in IBS-D patients through tandem mass tag (TMT)-based proteomics for the first time, aiming to reveal the pathogenesis and provide evidence for diagnosis and treatment of IBS-D. Five IBS-D patients and five healthy subjects were selected, biopsy tissue samples from the junction of sigmoid and rectum were analyzed by TMT proteomics. Differentially expressed proteins were obtained and bioinformatics analysis was performed. Furthermore, parallel reaction monitoring (PRM) and q-PCR detection were applied to validate the differentially expressed proteins. Eighty differentially expressed proteins were screened, 48 of which were up-regulated and 32 were down-regulated (fold change >1.2, P < 0.05). Bioinformatics analysis showed that these proteins were significantly enriched in the nutrient ingestion pathways which are related to immune molecules. SELENBP1, VSIG2, HMGB1, DHCR7, BCAP31 and other molecules were significantly changed. Our study revealed the underlying mechanisms of IBS-D intestinal dysfunction. SIGNIFICANCE: Irritable bowel syndrome with diarrhea (IBS-D) is a worldwide chronic intestinal disease with no definite diagnostic markers. It is still a challenge to accurately locate the pathogenesis of patients for appropriate treatment strategy. Established proteomics studies of IBS-D are only based on urine, blood, or tissue samples from animals. Our study was the first TMT proteomics analysis on intestinal biopsy tissues of patients with IBS-D, which revealed the changes of molecular spectrum of actual intestinal conditions in patients with IBS-D. Some important molecules and signaling pathways have been found abnormal in our study, which were related with nutrient uptake. They not only provided preliminary clues for low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) intolerance, an unsolved conundrum of IBS-D, but also revealed obscure problems of protein, lipid, and other nutrients ingestion in IBS-D patients. Some of these differentially expressed molecules have been preliminarily verified, and will may be potential candidate molecules for diagnostic markers of IBS-D.

Protective Role of IRBIT on Sodium Bicarbonate Cotransporter-n1 for Migratory Cancer Cells

IP₃ receptor-binding protein released with IP₃ (IRBIT) interacts with various ion channels and transporters. An electroneutral type of sodium bicarbonate cotransporter, NBCn1, participates in cell migration, and its enhanced expression is related to cancer metastasis. The effect of IRBIT on NBCn1 and its relation to cancer cell migration remain obscure. We therefore aimed to determine the effect of IRBIT on NBCn1 and the regulation of cancer cell migration due to IRBIT-induced alterations in NBCn1 activity. Overexpression of IRBIT enhanced cancer cell migration and NBC activity. Knockdown of IRBIT or NBCn1 and treatment with an NBC-specific inhibitor, S0859, attenuated cell migration. Stimulation with oncogenic epidermal growth factor enhanced the expression of NBCn1 and migration of cancer cells by recruiting IRBIT. The recruited IRBIT stably maintained the expression of the NBCn1 transporter machinery in the plasma membrane. Combined inhibition of IRBIT and NBCn1 dramatically inhibited the migration of cancer cells. Combined modulation of IRBIT and NBCn1 offers an effective strategy for attenuating cancer metastasis.

Activation of mouse NBCe1-B by Xenopus laevis and mouse IRBITs: Role of the variable Nt appendage of IRBITs

The IP3 receptor binding protein released with inositol 1,4,5-trisphosphate (IRBIT) plays important roles in the regulation of intracellular Ca²⁺ signaling and intracellular pH. The mammals express two IRBIT paralogs, i.e., IRBIT1 (encoded by AHCYL1) and IRBIT2 (encoded by AHCYL2). The clawed frog Xenopus laevis oocyte is widely used for biophysical studies on ion channels and transporters. It remains unknown whether endogenous IRBIT is expressed in Xenopus oocytes. Here, we cloned from frog oocyte irbit2.L and irbit2.S, orthologs of mammalian IRBIT2. When over-expressed, the frog IRBITs powerfully stimulate the electrogenic Na⁺/HCO₃^- cotransporter NBCe1-B as mouse IRBIT2-V2 does. Expression of an isolated Nt fragment of NBCe1-B containing the IRBIT-binding domain greatly decreases NBCe1-B activity in oocytes, suggesting that the basal activity of NBCe1-B contains a large component derived from the stimulation by endogenous frog IRBIT. The frog IRBITs are highly homologous to the mammalian ones in the carboxyl-terminal region, but varies greatly in the amino-terminal (Nt) appendage. Interestingly, truncation study showed that the Nt appendage of IRBIT1 and the long Nt appendage of IRBIT2-V2 modestly enhance, whereas the short Nt appendage of IRBIT2-V4 greatly inhibits the functional interaction between IRBIT and NBCe1-B. Finally, Ala-substitution of Ser68, a key phosphorylation site in the PEST domain of IRBIT, causes distinct functional consequences depending on the structural context of the Nt appendage in different IRBIT isoforms. We conclude that the Nt appendage of IRBITs is not necessary for, but plays an important regulatory role in the functional interaction between IRBIT and NBCe1-B.

Consensus report of the 8 and 9th Weinman Symposia on Gene x Environment Interaction in carcinogenesis: novel opportunities for precision medicine

The relative contribution of intrinsic genetic factors and extrinsic environmental ones to cancer aetiology and natural history is a lengthy and debated issue. Gene-environment interactions (G x E) arise when the combined presence of both a germline genetic variant and a known environmental factor modulates the risk of disease more than either one alone. A panel of experts discussed our current understanding of cancer aetiology, known examples of G × E interactions in cancer, and the expanded concept of G × E interactions to include somatic cancer mutations and iatrogenic environmental factors such as anti-cancer treatment. Specific genetic polymorphisms and genetic mutations increase susceptibility to certain carcinogens and may be targeted in the near future for prevention and treatment of cancer patients with novel molecularly based therapies. There was general consensus that a better understanding of the complexity and numerosity of G × E interactions, supported by adequate technological, epidemiological, modelling and statistical resources, will further promote our understanding of cancer and lead to novel preventive and therapeutic approaches.

Remodeling of Ca2+ signaling in cancer: Regulation of inositol 1,4,5-trisphosphate receptors through oncogenes and tumor suppressors

The calcium ion (Ca²⁺) is a ubiquitous intracellular signaling molecule that regulates diverse physiological and pathological processes, including cancer. Increasing evidence indicates that oncogenes and tumor suppressors regulate the Ca²⁺ transport systems. Inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs) are IP₃-activated Ca²⁺ release channels located on the endoplasmic reticulum (ER). They play pivotal roles in the regulation of cell death and survival by controlling Ca²⁺ transfer from the ER to mitochondria through mitochondria-associated ER membranes (MAMs). Optimal levels of Ca²⁺ mobilization to mitochondria are necessary for mitochondrial bioenergetics, whereas excessive Ca²⁺ flux into mitochondria causes loss of mitochondrial membrane integrity and apoptotic cell death. In addition to well-known functions on outer mitochondrial membranes, B-cell lymphoma 2 (Bcl-2) family proteins are localized on the ER and regulate IP₃Rs to control Ca²⁺ transfer into mitochondria. Another regulatory protein of IP₃R, IP₃R-binding protein released with IP₃ (IRBIT), cooperates with or counteracts the Bcl-2 family member depending on cellular states. Furthermore, several oncogenes and tumor suppressors, including Akt, K-Ras, phosphatase and tensin homolog (PTEN), promyelocytic leukemia protein (PML), BRCA1, and BRCA1 associated protein 1 (BAP1), are localized on the ER or at MAMs and negatively or positively regulate apoptotic cell death through interactions with IP₃Rs and regulation of Ca²⁺ dynamics. The remodeling of Ca²⁺ signaling by oncogenes and tumor suppressors that interact with IP₃Rs has fundamental roles in the pathology of cancers.

Splicing variation of Long-IRBIT determines the target selectivity of IRBIT family proteins

IRBIT [inositol 1,4,5-trisphosphate receptor (IP₃R) binding protein released with inositol 1,4,5-trisphosphate (IP₃)] is a multifunctional protein that regulates several target molecules such as ion channels, transporters, polyadenylation complex, and kinases. Through its interaction with multiple targets, IRBIT contributes to calcium signaling, electrolyte transport, mRNA processing, cell cycle, and neuronal function. However, the regulatory mechanism of IRBIT binding to particular targets is poorly understood. Long-IRBIT is an IRBIT homolog with high homology to IRBIT, except for a unique N-terminal appendage. Long-IRBIT splice variants have different N-terminal sequences and a common C-terminal region, which is involved in multimerization of IRBIT and Long-IRBIT. In this study, we characterized IRBIT and Long-IRBIT splice variants (IRBIT family). We determined that the IRBIT family exhibits different mRNA expression patterns in various tissues. The IRBIT family formed homo- and heteromultimers. In addition, N-terminal splicing of Long-IRBIT changed the protein stability and selectivity to target molecules. These results suggest that N-terminal diversity of the IRBIT family and various combinations of multimer formation contribute to the functional diversity of the IRBIT family.

IRBIT controls apoptosis by interacting with the Bcl-2 homolog, Bcl2l10, and by promoting ER-mitochondria contact

IRBIT is a molecule that interacts with the inositol 1,4,5-trisphosphate (IP₃)-binding pocket of the IP₃ receptor (IP₃R), whereas the antiapoptotic protein, Bcl2l10, binds to another part of the IP₃-binding domain. Here we show that Bcl2l10 and IRBIT interact and exert an additive inhibition of IP₃R in the physiological state. Moreover, we found that these proteins associate in a complex in mitochondria-associated membranes (MAMs) and that their interplay is involved in apoptosis regulation. MAMs are a hotspot for Ca²⁺ transfer between endoplasmic reticulum (ER) and mitochondria, and massive Ca²⁺ release through IP₃R in mitochondria induces cell death. We found that upon apoptotic stress, IRBIT is dephosphorylated, becoming an inhibitor of Bcl2l10. Moreover, IRBIT promotes ER mitochondria contact. Our results suggest that by inhibiting Bcl2l10 activity and promoting contact between ER and mitochondria, IRBIT facilitates massive Ca²⁺ transfer to mitochondria and promotes apoptosis. This work then describes IRBIT as a new regulator of cell death.

Ahcyl2 upregulates NBCe1-B via multiple serine residues of the PEST domain-mediated association

Inositol-1,4,5-triphosphate [IP₃] receptors binding protein released with IP₃ (IRBIT) was previously reported as an activator of NBCe1-B. Recent studies have characterized IRBIT homologue S-Adenosylhomocysteine hydrolase-like 2 (AHCYL2). AHCYL2 is highly homologous to IRBIT (88%) and heteromerizes with IRBIT. The two important domains in the N-terminus of AHCYL2 are a PEST domain and a coiled-coil domain which are highly comparable to those in IRBIT. Therefore, in this study, we tried to identify the role of those domains in mouse AHCYL2 (Ahcyl2), and we succeeded in identifying PEST domain of Ahcyl2 as a regulation region for NBCe1-B activity. Site directed mutagenesis and coimmunoprecipitation assay showed that NBCe1-B binds to the N-terminal Ahcyl2-PEST domain, and its binding is determined by the phosphorylation of 4 critical serine residues (Ser151, Ser154, Ser157, and Ser160) in Ahcyl2 PEST domain. Also we revealed that 4 critical serine residues in Ahcyl2 PEST domain are indispensable for the activation of NBCe1-B using measurement of intracellular pH experiment. Thus, these results suggested that the NBCe1-B is interacted with 4 critical serine residues in Ahcyl2 PEST domain, which play an important role in intracellular pH regulation through NBCe1-B.

IRBIT Interacts with the Catalytic Core of Phosphatidylinositol Phosphate Kinase Type Iα and IIα through Conserved Catalytic Aspartate Residues

Phosphatidylinositol phosphate kinases (PIPKs) are lipid kinases that generate phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂), a critical lipid signaling molecule that regulates diverse cellular functions, including the activities of membrane channels and transporters. IRBIT (IP₃R-binding protein released with inositol 1,4,5-trisphosphate) is a multifunctional protein that regulates diverse target proteins. Here, we report that IRBIT forms signaling complexes with members of the PIPK family. IRBIT bound to all PIPK isoforms in heterologous expression systems and specifically interacted with PIPK type Iα (PIPKIα) and type IIα (PIPKIIα) in mouse cerebellum. Site-directed mutagenesis revealed that two conserved catalytic aspartate residues of PIPKIα and PIPKIIα are involved in the interaction with IRBIT. Furthermore, phosphatidylinositol 4-phosphate, Mg²⁺, and/or ATP interfered with the interaction, suggesting that IRBIT interacts with catalytic cores of PIPKs. Mutations of phosphorylation sites in the serine-rich region of IRBIT affected the selectivity of its interaction with PIPKIα and PIPKIIα. The structural flexibility of the serine-rich region, located in the intrinsically disordered protein region, is assumed to underlie the mechanism of this interaction. Furthermore, in vitro binding experiments and immunocytochemistry suggest that IRBIT and PIPKIα interact with the Na⁺/HCO₃⁻ cotransporter NBCe1-B. These results suggest that IRBIT forms signaling complexes with PIPKIα and NBCe1-B, whose activity is regulated by PI(4,5)P₂.

The IP3 R Binding Protein Released With Inositol 1,4,5-Trisphosphate Is Expressed in Rodent Reproductive Tissue and Spermatozoa

Besides its capacity to inhibit the 1,4,5-trisphosphate (IP3) receptor, the regulatory protein IRBIT (IP3 receptor binding protein released with IP3) is also able to control the activity of numerous ion channels and electrolyte transporters and thereby creates an optimal electrolyte composition of various biological fluids. Since a reliable execution of spermatogenesis and sperm maturation critically depends on the establishment of an adequate microenvironment, the expression of IRBIT in male reproductive tissue was examined using immunohistochemical approaches combined with biochemical fractionation methods. The present study documents that IRBIT is expressed in Leydig and Sertoli cells. In addition, pronounced IRBIT expression was detected in sperm precursors during early stages of spermatogenesis as well as in spermatozoa. Analyzing tissue sections of rodent epididymides, IRBIT was found to co-localize with the proton pumping V-ATPase and the cystic fibrosis transmembrane conductance regulator (CFTR) at the apical surface of narrow and clear cells. A similar co-localization of IRBIT with CFTR was also observed for Sertoli cells and developing germ cells. Remarkably, assaying caudal sperm in immunogold electron microscopy, IRBIT was found to localize to the acrosomal cap and the flagellum as well as to the sperm nucleus; moreover, a prominent oligomerization was observed for spermatozoa. The pronounced occurrence of IRBIT in the male reproductive system and mature spermatozoa indicates a potential role for IRBIT in establishing the essential luminal environment for a faithful execution of spermatogenesis and epididymal sperm maturation, and suggest a participation of IRBIT during maturation steps after ejaculation and/or the final fertilization process.

Regulators of Slc4 bicarbonate transporter activity

The Slc4 family of transporters is comprised of anion exchangers (AE1-4), Na⁺-coupled bicarbonate transporters (NCBTs) including electrogenic Na/bicarbonate cotransporters (NBCe1 and NBCe2), electroneutral Na/bicarbonate cotransporters (NBCn1 and NBCn2), and the electroneutral Na-driven Cl-bicarbonate exchanger (NDCBE), as well as a borate transporter (BTR1). These transporters regulate intracellular pH (pH_i) and contribute to steady-state pH_i, but are also involved in other physiological processes including CO₂ carriage by red blood cells and solute secretion/reabsorption across epithelia. Acid-base transporters function as either acid extruders or acid loaders, with the Slc4 proteins moving HCO⁻₃ either into or out of cells. According to results from both molecular and functional studies, multiple Slc4 proteins and/or associated splice variants with similar expected effects on pH_i are often found in the same tissue or cell. Such apparent redundancy is likely to be physiologically important. In addition to regulating pH_i, a HCO⁻₃ transporter contributes to a cell's ability to fine tune the intracellular regulation of the cotransported/exchanged ion(s) (e.g., Na⁺ or Cl⁻). In addition, functionally similar transporters or splice variants with different regulatory profiles will optimize pH physiology and solute transport under various conditions or within subcellular domains. Such optimization will depend on activated signaling pathways and transporter expression profiles. In this review, we will summarize and discuss both well-known and more recently identified regulators of the Slc4 proteins. Some of these regulators include traditional second messengers, lipids, binding proteins, autoregulatory domains, and less conventional regulators. The material presented will provide insight into the diversity and physiological significance of multiple members within the Slc4 gene family.

IRBIT: a regulator of ion channels and ion transporters

IRBIT (also called AHCYL1) was originally identified as a binding protein of the intracellular Ca(2+) channel inositol 1,4,5-trisphosphate (IP3) receptor and functions as an inhibitory regulator of this receptor. Unexpectedly, many functions have subsequently been identified for IRBIT including the activation of multiple ion channels and ion transporters, such as the Na(+)/HCO3(-) co-transporter NBCe1-B, the Na(+)/H(+) exchanger NHE3, the Cl(-) channel cystic fibrosis transmembrane conductance regulator (CFTR), and the Cl(-)/HCO3(-) exchanger Slc26a6. The characteristic serine-rich region in IRBIT plays a critical role in the functions of this protein. In this review, we describe the evolution, domain structure, expression pattern, and physiological roles of IRBIT and discuss the potential molecular mechanisms underlying the coordinated regulation of these diverse ion channels/transporters through IRBIT. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

AHCYL2 (long-IRBIT) as a potential regulator of the electrogenic Na(+)-HCO3(-) cotransporter NBCe1-B

Although AHCYL2 (long-IRBIT) is highly homologous to IRBIT, which regulates ion-transporting proteins including the electrogenic Na(+)-HCO3(-) cotransporter NBCe1-B, its functions are poorly understood. Here, we found that AHCYL2 interacts with NBCe1-B in bovine parotid acinar cells using yeast two-hybrid, immunofluorescence confocal microscopy and co-immunoprecipitation analyses. Whole-cell patch-clamp experiments revealed that co-expression of AHCYL2 reduces the apparent affinity for intracellular Mg(2+) in inhibition of NBCe1-B currents specifically in a HCO3(-)-deficient cellular condition. Our data unveil AHCYL2 as a potential regulator of NBCe1-B in mammalian cells. We propose that cytosolic ionic condition appropriate for AHCYL2 to function might be different from IRBIT.

The WNK/SPAK and IRBIT/PP1 pathways in epithelial fluid and electrolyte transport

Fluid and electrolyte homeostasis is a fundamental physiological function required for survival and is associated with a plethora of diseases when aberrant. Systemic fluid and electrolyte composition is regulated by the kidney, and all secretory epithelia generate biological fluids with defined electrolyte composition by vectorial transport of ions and the obligatory water. A major regulatory pathway that immerged in the last several years is regulation of ion transporters by the WNK/SPAK kinases and IRBIT/PP1 pathways. The IRBIT/PP1 pathway functions to reverse the effects of the WNK/SPAK kinases pathway, as was demonstrated for NBCe1-B and CFTR. Since many transporters involved in fluid and electrolyte homeostasis are affected by PP1 and/or calcineurin, it is possible that WNK/SPAK and IRBIT/PP1 form a common regulatory pathway to tune the activity of fluid and electrolyte transport in response to physiological demands.

AHCYL1 is mediated by estrogen-induced ERK1/2 MAPK cell signaling and microRNA regulation to effect functional aspects of the avian oviduct

S-adenosylhomocysteine hydrolase-like protein 1 (AHCYL1), also known as IP(3) receptor-binding protein released with IP(3) (IRBIT), regulates IP(3)-induced Ca(2+) release into the cytoplasm of cells. AHCYL1 is a critical regulator of early developmental stages in zebrafish, but little is known about the function of AHCYL1 or hormonal regulation of expression of the AHCYL1 gene in avian species. Therefore, we investigated differential expression profiles of the AHCYL1 gene in various adult organs and in oviducts from estrogen-treated chickens. Chicken AHCYL1 encodes for a protein of 540 amino acids that is highly conserved and has considerable homology to mammalian AHCYL1 proteins (>94% identity). AHCYL1 mRNA was expressed abundantly in various organs of chickens. Further, the synthetic estrogen agonist induced AHCYL1 mRNA and protein predominantly in luminal and glandular epithelial cells of the chick oviduct. In addition, estrogen activated AHCYL1 through the ERK1/2 signal transduction cascade and that activated expression of AHCYL1 regulated genes affecting oviduct development in chicks as well as calcium release in epithelial cells of the oviduct. Also, microRNAs, miR-124a, miR-1669, miR-1710 and miR-1782 influenced AHCYL1 expression in vitro via its 3'-UTR which suggests that post-transcriptional events are involved in the regulation of AHCYL1 expression in the chick oviduct. In conclusion, these results indicate that AHCYL1 is a novel estrogen-stimulated gene expressed in epithelial cells of the chicken oviduct that likely affects growth, development and calcium metabolism of the mature oviduct of hens via an estrogen-mediated ERK1/2 MAPK cell signaling pathway.

Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion

Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.

IRBIT: it is everywhere

IRBIT (IP(3)Rs binding protein released with IP(3)) is a protein originally identified by the Mikoshiba group as an inhibitor of IP(3) receptors function. Subsequently it was found to have multiple functions and regulate the activity of diverse proteins, including regulation of HCO(3)(-) transporters to coordinate epithelial HCO(3)(-) secretion and to determine localization of the Fip1 subunit of the CPSF complex to regulate mRNA processing. This review highlights the remarkably divers functions of IRBIT that are likely only a fraction of all the potential functions of this protein.

Inositol 1,4,5-triphosphate receptor-binding protein released with inositol 1,4,5-triphosphate (IRBIT) associates with components of the mRNA 3' processing machinery in a phosphorylation-dependent manner and inhibits polyadenylation

IRBIT is a recently identified protein that modulates the activities of both inositol 1,4,5-triphosphate receptor and pancreas-type Na(+)/HCO(3)(-) cotransporter 1, and the multisite phosphorylation of IRBIT is required for achieving this modulatory action. Here, we report the identification of the cleavage and polyadenylation specificity factor (CPSF), which is a multi-protein complex involved in 3' processing of mRNA precursors, as an additional binding partner for IRBIT. We found that IRBIT interacted with CPSF and was recruited to an exogenous polyadenylation signal-containing RNA. The main target for IRBIT in CPSF was Fip1 subunit, and the phosphorylation of the serine-rich region of IRBIT was required both for direct association with Fip1 in vitro and for redistribution of Fip1 into the cytoplasm of intact cells. Furthermore, tert-butylhydroquinone (tBHQ), an agent that induces oxidative stress, increased the phosphorylation level of IRBIT in vivo and in parallel enhanced the interaction between IRBIT and CPSF and promoted the cytoplasmic distribution of endogenous Fip1. In addition to CPSF, IRBIT interacted in vitro with poly(A) polymerase (PAP), which is the enzyme recruited by CPSF to elongate the poly(A) tail, and inhibited PAP activity in a phosphorylation-dependent manner. These findings raise the possibility that IRBIT modulates the polyadenylation state of specific mRNAs, both by controlling the cytoplasmic/nuclear partitioning of Fip1 and by inhibiting PAP activity, in response to a stimulus that alters its phosphorylation state.