HeLa cDNA Library Research Articles

SPOP promotes ATF2 ubiquitination and degradation to suppress prostate cancer progression

BackgroundNext-generation sequencing of the exome and genome of prostate cancers has identified numerous genetic alterations. SPOP (Speckle-type POZ Protein) is one of the most frequently mutated genes in primary prostate cancer, suggesting that SPOP may be a potential driver of prostate cancer. The aim of this work was to investigate how SPOP mutations contribute to prostate cancer development and progression.MethodsTo identify molecular mediators of the tumor suppressive function of SPOP, we performed a yeast two-hybrid screen in a HeLa cDNA library using the full-length SPOP as bait. Immunoprecipitation and Western Blotting were used to analyze the interaction between SPOP and ATF2. Cell migration and invasion were determined by Transwell assays. Immunohistochemistry were used to analyze protein levels in patients’ tumor samples.ResultsHere we identified ATF2 as a bona fide substrate of the SPOP-CUL3-RBX1 E3 ubiquitin ligase complex. SPOP recognizes multiple Ser/Thr (S/T)-rich degrons in ATF2 and triggers ATF2 degradation via the ubiquitin-proteasome pathway. Strikingly, prostate cancer-associated mutants of SPOP are defective in promoting ATF2 degradation in prostate cancer cells and contribute to facilitating prostate cancer cell proliferation, migration and invasion.ConclusionSPOP promotes ATF2 ubiquitination and degradation, and ATF2 is an important mediator of SPOP inactivation-induced cell proliferation, migration and invasion.

Plk1 interacts with RNF2 and promotes its ubiquitin‑dependent degradation.

Ring finger protein2 (RNF2), also known as RING2 or RING1B, displays oncogenic functions in different types of cancers, yet, the function of RNF2 during mitosis has not been evaluated. A yeast two‑hybrid screen was undertaken using a human HeLa cDNA library to explore and identify proteins that interact with RNF2. Several positive clones, including Polo‑like kinase1 (Plk1), a critical regulator of mitosis, were identified. The interaction between RNF2 and Plk1 was confirmed using a β‑galactosidase and growth test in selective media, invitro glutathione S‑transferase pull‑down, and invivo immunoprecipitation assays. Moreover, we confirmed that RNF2 co‑localized with Plk1 at mitotic chromosomes in the prometaphase and metaphase using an immunofluorescence assay. In addition, our results revealed that Plk1 kinase activity was required for ubiquitin‑dependent degradation of RNF2. These findings provide a new clue for understanding the function of RNF2 during mitotic regulation and tumorigenesis.

A yeast two-hybrid screen reveals a strong interaction between the Legionella chaperonin Hsp60 and the host cell small heat shock protein Hsp10.

L. pneumophila is an intracellular bacterium that replicates inside a membrane-bound vacuole called Legionella-containing vacuole (LCV), where it plentifully liberates its HtpB chaperonin. From LCV, HtpB reaches the host cell cytoplasm, where it interacts with SAMDC, a cytoplasmic protein required for synthesis of host polyamines that are important for intracellular growth of L. pneumophila. Additionally, cytoplasmic expression of HtpB in S. cerevisiae induces pseudohyphal growth, and in mammalian cells recruits mitochondria to LCV, and modifies actin microfilaments organization. This led us to hypothesize here that HtpB recruits a protein(s) from eukaryotic cells that is involved in the emergence of the aforementioned phenotypes. To identify this protein, a commercially available HeLa cDNA library was screened using a yeast two-hybrid system. Approximately 5×10(6) yeast clones carrying HeLa cDNA library plasmid were screened. Twenty-one positive clones were identified. DNA sequence analysis revealed that all of these positive clones encoded the mammalian small heat shock protein Hsp10. Based on the fact that chaperonions are required to interact with co-chaperonins to function properly in protein folding, we believe that HtpB recruits the host cell Hsp10 to appropriately interact with SAMDC and to induce the multifunction phenotypes deemed important in L. pneumophila pathogenesis.

Fas-associated factor (Faf1) is a novel CD40 interactor that regulates CD40-induced NF-κB activation via a negative feedback loop.

CD40-induced signalling through ligation with its natural ligand (CD40L/CD154) is dependent on recruitment of TRAF molecules to the cytoplasmic domain of the receptor. Here, we applied the yeast two-hybrid system to examine whether other proteins can interact with CD40. Fas-Associated Factor 1(FAF1) was isolated from a HeLa cDNA library using the CD40 cytoplasmic tail (216–278 aa) as a bait construct. FAF1 was able to interact with CD40 both in vitro and in vivo. The FAF1 N-terminal domain was sufficient to bind CD40 and required the TRAF6-binding domain within the cytoplasmic tail of CD40 for binding. CD40 ligation induced FAF1 expression in an NFκB-dependent manner. Knockdown of FAF1 prolonged CD40-induced NFκB, whereas overexpression of FAF1 suppressed CD40-induced NFκB activity and this required interaction of FAF1 with the CD40 receptor via its FID domain. Thus, we report a novel role for FAF1in regulating CD40-induced NFκB activation via a negative feedback loop. Loss of FAF1 function in certain human malignancies may contribute to oncogenesis through unchecked NFκB activation, and further understanding of this process may provide a biomarker of NFκB-targeted therapies for such malignancies.

Identification of an endoplasmic reticulum membrane protein interacting with DNA polymerase beta by a yeast two-hybrid screen.

Base excision repair (BER) is a key pathway for maintaining genomic stability. A key enzyme in the BER pathway is DNA polymerase beta (polbeta). It has been shown that more than 11% of breast, bladder, esophageal, colon, and gastric cancer samples studied so far exhibit polbeta mutation. A truncated form of polbeta, polbetadelta (exon 11 deletion), identified in a colon tumour sample, exhibited dominant negative activity. Using this polbetadelta as bait, we screened a HeLa cDNA library for any interacting protein(s) in the yeast two-hybrid (Y2H) system. Polbetadelta was cloned into a pGBKT7 vector (pGBKT7-polbetadelta). pGBKT7-polbetadelta was transformed into the yeast strain AH109. Then the cDNA library was co-transformed into AH109/pGBKT7-polbetadelta and screened by the selection procedure. The yeast-purified plasmids were transformed into Escherichia coli. Plasmid DNA was isolated from the colonies, purified, digested with Sma I and Sal I, and the fragments were sequenced. Four positive clones were obtained. Out of these, three proteins were already known to interact with polbeta (XRCC1, MGC5306, and AP endonuclease 1). The only member previously not known to interact with polbeta was phosphatidylinositol glycosylase type S (PIGS). PIGS is a 64-kDa membrane protein, encoded in chromosome 17. The PIGS protein interacts also with wild-type polbeta which was confirmed by co-immunoprecipitation and Western blot analysis. The role of the newly identified protein in the dominant negative function of the variant form of polbeta remains to be seen.

Identification of Tudor domain containing 7 protein as a novel partner and a substrate for ribosomal protein S6 kinaseS – S6K1 and S6K2

ribosomal protein S6 kinases (S6ks) are principal regulators of cell size, growth and metabolism. Signaling via the PI3k/mtOr pathway mediates the activation of S6ks in response to various mitogenic stimuli, nutrients and stresses. to date, the regulation and cellular functions of S6ks are not fully understood. Our aim was to investigate and characterize the interaction of S6ks with the novel binding partner of S6ks, tudor domain containing 7 protein (tdrd7), which is a scaffold protein detected in complexes involved in the regulation of cytoskeleton dynamics, mrNa transport and translation, non-coding pirNas processing and transposons silencing. this interaction was initially detected in the yeast two-hybrid screening of hela cdNa library and further confirmed by pull-down and co-immunoprecipitation assays. In addition we demonstrated that tdrd7 can form a complex with other isoform of S6k S6k2. Notably, both isoforms of S6k were found to phosphorylate tdrd7 in vitro at multiple phosphorylation sites. altogether, these findings demonstrate that tdrd7 is a novel substrate of S6ks, suggesting the involvement of S6k signaling in the regulation of tdrd7 cellular functions.

Interaction of 14-3-3σ with KCMF1 suppresses the proliferation and colony formation of human colon cancer stem cells

To investigate the biological function of 14-3-3σ protein and to look for proteins that interact with 14-3-3σ protein in colon cancer stem cells. Reverse transcription polymerase chain reaction was performed to amplify the 14-3-3σ gene from the mRNA of colon cancer stem cells. The gene was then cloned into the pGEM-T vector. After being sequenced, the target gene 14-3-3σ was cut from the pGEM-T vector and cloned into the pGBKT7 yeast expression plasmid. Then, the bait plasmid pGBKT7-14-3-3σ was transformed into the yeast strain AH109. After the expression of the pGBKT7-14-3-3σ fusion protein in the AH109 yeast strain was accomplished, a yeast two-hybrid screening assay was performed by mating AH109 with Y187 that contained a HeLa cDNA library plasmid. The interaction between the 14-3-3σ protein and the proteins obtained from positive colonies was further confirmed by repeating the yeast two-hybrid screen. After extracting and sequencing the plasmids from the positive colonies, we performed a bioinformatics analysis. A coimmunoprecipitation assay was performed to confirm the interaction between 14-3-3σ and the proteins obtained from the positive colonies. Finally, we constructed 14-3-3σ and potassium channel modulatory factor 1 (KCMF1) siRNA expression plasmids and transfected them into colon cancer stem cells. The bait plasmid pGBKT7-14-3-3σ was constructed successfully, and the 14-3-3σ protein had no toxic or autonomous activation effect on the yeast. Nineteen true-positive colonies were selected and sequenced, and their full-length sequences were obtained. We searched for homologous DNA sequences for these sequences from GenBank. Among the positive colonies, four coding genes with known functions were obtained, including KCMF1, quinone oxidoreductase (NQO2), hydroxyisobutyrate dehydrogenase (HIBADH) and 14-3-3σ. For the subsequent coimmunoprecipitation assay, the plasmids PCDEF-Flag-14-3-3σ, PCDEF-Myc-KCMF1, PCDEF-Myc-NQO2 and PCDEF-Myc-HIBADH were successfully constructed, and the sequences were further confirmed by DNA sequencing. The Fugene 6 reagent was used to transfect the plasmids, and fluorescence-activated cell sorting analysis showed the transfection efficiency was 97.8% after 48 h. The HEK 293FT cells showed the stable expression of the PCDEF-Flag-14-3-3σ, PCDEF-Myc-KCMF1, PCDEF-Myc-NQO2 and PCDEF-Myc-HIBADH plasmids. After anti-Myc antibody immunoprecipitation with Myc-KCMF1, Myc-NQO2 and Myc-HIBADH from cell lysates, the presence of Flag-14-3-3σ protein in the immunoprecipitated complex was determined by western blot analysis. The knock-down expression of the 14-3-3σ and KCMF1 proteins significantly inhibited cell proliferation and colony formation of SW1116csc. Genes of the proteins that interacted with 14-3-3σ were successfully screened from a HeLa cDNA library. KCMF1 and 14-3-3σ protein may affect the proliferation and colony formation of human colon cancer stem cells.

HEXIM1-binding elements on mRNAs identified through transcriptomic SELEX and computational screening

The positive transcription elongation factor b (P-TEFb) is one of the main regulatory factors of the transcription mediated by RNA polymerase II (RNAPII). P-TEFb promotes transcriptional elongation by phosphorylating its targets, which include the C-terminal domain of RNAPII. The activity of P-TEFb is negatively regulated by an RNA-binding protein HEXIM1 in association with 7SK snRNA. To search for other cellular RNAs that bind to HEXIM1, we used systematic evolution of ligands by exponential enrichment (SELEX) with the HeLa cDNA library as the initial pool source. We identified cad mRNA as a HEXIM1-binding RNA and confirmed their association in HeLa cells. Invitro mutational analysis showed that cad mRNA binds to HEXIM1 through its bulged stem structure located in exon 11. In addition, a computational search revealed other RNAs with similar stem structures, including brd4 and tcf3 mRNAs, both of which were shown to be coimmunoprecipitable with anti-HEXIM1 antibody in HeLa cells. Our findings suggest a possible role for HEXIM1 in the regulation of specific gene expressions.

Effects of partner proteins on BCA2 RING ligase activity

BackgroundBCA2 is an E3 ligase linked with hormone responsive breast cancers. We have demonstrated previously that the RING E3 ligase BCA2 has autoubiquitination activity and is a very unstable protein. Previously, only Rab7, tetherin, ubiquitin and UBC9 were known to directly interact with BCA2.MethodsHere, additional BCA2 binding proteins were found using yeast two-hybrid and bacterial-II-hybrid screening techniques with Human breast and HeLa cDNA libraries. Co-expression of these proteins was analyzed through IHC of TMAs. Investigation of the molecular interactions and effects were examined through a series of in vivo and in vitro assays.ResultsTen unique BCA2 interacting proteins were identified, two of which were hHR23a and 14-3-3sigma. Both hHR23a and 14-3-3sigma are co-expressed with BCA2 in breast cancer cell lines and patient breast tumors (n = 105). hHR23a and BCA2 expression was significantly correlated (P = < 0.0001 and P = 0.0113) in both nucleus and cytoplasm. BCA2 expression showed a statistically significant correlation with tumor grade. High cytoplasmic hHR23a trended towards negative nodal status. Binding to BCA2 by hHR23a and 14-3-3sigma was confirmed in vitro using tagged partner proteins and BCA2. hHR23a and 14-3-3sigma effect the autoubiquitination and auto-degradation activity of BCA2. Ubiquitination of hHR23a-bound BCA2 was found to be dramatically lower than that of free BCA2, suggesting that hHR23a promotes the stabilization of BCA2 by inactivating its autoubiquitination activity, without degradation of hHR23a. On the other hand, phosphorylated BCA2 protein is stabilized by interaction with 14-3-3sigma both with and without proteasome inhibitor MG-132 suggesting that BCA2 is regulated by multiple degradation pathways.ConclusionsThe interaction between BCA2 and hHR23a in breast cancer cells stabilizes BCA2. High expression of BCA2 is correlated with grade in breast cancer, suggesting regulation of this E3 ligase is important to cancer progression.

Protein Kinase D Regulates Cofilin Activity through p21-activated Kinase 4

Dynamic reorganization of the actin cytoskeleton at the leading edge is required for directed cell migration. Cofilin, a small actin-binding protein with F-actin severing activities, is a key enzyme initiating such actin remodeling processes. Cofilin activity is tightly regulated by phosphorylation and dephosphorylation events that are mediated by LIM kinase (LIMK) and the phosphatase slingshot (SSH), respectively. Protein kinase D (PKD) is a serine/threonine kinase that inhibits actin-driven directed cell migration by phosphorylation and inactivation of SSH. Here, we show that PKD can also regulate LIMK through direct phosphorylation and activation of its upstream kinase p21-activated kinase 4 (PAK4). Therefore, active PKD increases the net amount of phosphorylated inactive cofilin in cells through both pathways. The regulation of cofilin activity at multiple levels may explain the inhibitory effects of PKD on barbed end formation as well as on directed cell migration.

Studies on Human DNA Polymerase ϵ and GINS Complex and Their Role in DNA Replication

Studies on Human DNA Polymerase ϵ and GINS Complex and Their Role in DNA Replication

A Novel Cytoplasmic Adaptor for Retinoic Acid Receptor (RAR) and Thyroid Receptor Functions as a Derepressor of RAR in the Absence of Retinoic Acid*

In most mammalian cells, the retinoic acid receptor (RAR) is nuclear rather than cytoplasmic, regardless of its cognate ligand, retinoic acid (RA). In testis Sertoli cells, however, RAR is retained in the cytoplasm and moves to the nucleus only when RA is supplied. This led us to identify a protein that regulates the translocation of RAR. From yeast two-hybrid screening, we identified a novel RAR-interacting protein called CART1 (cytoplasmic adaptor for RAR and TR). Systematic interaction assays using deletion mutants showed that the C-terminal CoRNR box of CART1 was responsible for the interaction with the NCoR binding region of RAR and TR. Such interaction was impaired in the presence of ligand RA, as further determined by GST pulldown assays in vitro and immunoprecipitation assays in vivo. Fluorescence microscopy showed that unliganded RAR was captured by CART1 in the cytoplasm, whereas liganded RAR was liberated and moved to the nucleus. Overexpression of CART1 blocked the transcriptional repressing activity of unliganded apoRAR, mediated by corepressor NCoR in the nucleus. CART1 siRNA treatment in a mouse Sertoli cell line, TM4, allowed RAR to move to the nucleus and blocked the derepressing function of CART1, suggesting that CART1 might be a cytoplasmic, testis-specific derepressor of RAR.

Influence of the Human Cohesion Establishment Factor Ctf4/AND-1 on DNA Replication

Ctf4/AND-1 is a highly conserved gene product required for both DNA replication and the establishment of sister chromatid cohesion. In this report, we examined the mechanism of action of human Ctf4 (hCtf4) in DNA replication both in vitro and in vivo. Our findings show that the purified hCtf4 exists as a dimer and that the hCtf4 SepB domain likely plays a primary role determining the dimeric structure. hCtf4 binds preferentially to DNA template-primer structures, interacts directly with the replicative DNA polymerases (alpha, delta, and epsilon), and markedly stimulates the polymerase activities of DNA polymerases alpha and epsilon in vitro. Depletion of hCtf4 in HeLa cells by small interfering RNA resulted in G(1)/S phase arrest. DNA fiber analysis revealed that cells depleted of hCtf4 exhibited a rate of DNA replication slower than cells treated with control small interfering RNA. These findings suggest that in human cells, hCtf4 plays an essential role in DNA replication and its ability to stimulate the replicative DNA polymerases may contribute to this effect.

Identification of novel PTEN-binding partners: PTEN interaction with fatty acid binding protein FABP4

PTEN is a tumor suppressor with dual protein and lipid-phosphatase activity, which is frequently deleted or mutated in many human advanced cancers. Recent studies have also demonstrated that PTEN is a promising target in type II diabetes and obesity treatment. Using C-terminal PTEN sequence in pEG202-NLS as bait, yeast two-hybrid screening on Mouse Embryo, Colon Cancer, and HeLa cDNA libraries was carried out. Isolated positive clones were validated by mating assay and identified through automated DNA sequencing and BLAST database searches. Sequence analysis revealed a number of PTEN-binding proteins linking this phosphatase to a number of different signaling cascades, suggesting that PTEN may perform other functions besides tumor-suppressing activity in different cell types. In particular, the interplay between PTEN function and adipocyte-specific fatty-acid-binding protein FABP4 is of notable interest. The demonstrable tautology of PTEN to FABP4 suggested a role for this phosphatase in the regulation of lipid metabolism and adipocyte differentiation. This interaction was further studied using coimmunoprecipitation and gel-filtration assays. Finally, based on Biacore assay, we have calculated the K(D) of PTEN-FABP4 complex, which is around 2.8 microM.

CK2 phosphorylates TNFAIP1 to affect its subcellular localization and interaction with PCNA

TNFAIP1 is a protein which can be induced by tumor necrosis factoralpha (TNFalpha) and interleukin-6 (IL-6), it may play roles in DNA synthesis, DNA repair, cell apoptosis and human diseases. However, very little has been known about how TNFAIP1 acts in these physiological processes. In this paper, CK2beta was identified as a partner of TNFAIP1 by screening the HeLa cDNA library in yeast two-hybrid system with TNFAIP1 as a bait. Furthermore, it was demonstrated that CK2 could phosphorylate TNFAIP1 in vitro and in vivo, which facilitated the distribution of TNFAIP1 in nucleus and enhanced its interaction with PCNA. It is suggested that the phosphorylation of TNFAIP1 may be required for its functions.

Identification of FANCA as a protein interacting with centromere-associated protein E

This study sought to isolate and identify proteins that interact with centromere-associated protein E (CENPE), provide new clues for exploring the function of CENP-E in cell cycle control and the pathogenesis of tumor. Yeast two-hybrid screen and regular molecular biologic techniques were undertaken to screen human HeLa cDNA library with the kinetochore binding domain of CENP-E. The bait from the C-terminus of CENP-E was created by subcloning methods to find out optimal candidate proteins that interact with the kinetochore binding domain of CENP-E. Eight novel CENP-E interacting proteins including Homo sapiens Fanconi anemia complementation group A (FANCA) were obtained. In yeast two-hybrid assay, the N-terminal 260 amino acids of FANCA were found to be necessary and sufficient for the interaction with the C-terminus of CENP-E. The interaction was confirmed by in vitro glutathione S-transferase pull-down assay and in vivo coimmunoprecipitation assay. Our finding of the interaction of CENP-E with FANCA demonstrates that CENP-E and FANCA may play important roles in the functional regulation of the mitotic checkpoint signal pathway.

Pin1 Catalyzes Conformational Changes of Thr-187 in p27Kip1 and Mediates Its Stability through a Polyubiquitination Process

The cis-trans peptidylprolyl isomerase Pin1 plays a critical role in regulating a subset of phosphoproteins by catalyzing conformational changes on the phosphorylated Ser/Thr-Pro motifs. The phosphorylation-directed ubiquitination is one of the major mechanisms to regulate the abundance of p27(Kip1). In this study, we demonstrate that Pin1 catalyzes the cis-trans conformational changes of p27(Kip1) and further mediates its stability through the polyubiquitination mechanism. Our results show that the phosphorylated Thr-187-Pro motif in p27(Kip1) is a key Pin1-binding site. In addition, NMR analyses show that this phosphorylated Thr-187-Pro site undergoes conformational change catalyzed by Pin1. Moreover, in Pin1 knock-out mouse embryonic fibroblasts, p27(Kip1) has a shorter lifetime and displays a higher degree of polyubiquitination than in Pin1 wild-type mouse embryonic fibroblasts, suggesting that Pin1 plays a critical role in regulating p27(Kip1) degradation. Additionally, Pin1 dramatically reduces the interaction between p27(Kip1) and Cks1, possibly via isomerizing the cis-trans conformation of p27(Kip1). Our study thus reveals a novel regulatory mechanism for p27(Kip1) stability and sheds new light on the biological function of Pin1 as a general regulator of protein stability.

Functional and Physical Interaction between Human Lactate Dehydrogenase B and Na+/H+ Exchanger Isoform 1

The ubiquitous plasma membrane Na+/H+ exchanger 1 (NHE1) is rapidly activated in response to various extracellular stimuli and maintains normal cytoplasmic pH. Yeast two‐hybrid screening was used in order to identify proteins interacting with NHE1 using its cytoplasmic domain as a bait from HeLa cDNA library. One of the interacting cDNA clones was human Lactate dehydrogenase B (LDHB). In vitro translated LDHB was pulled down together with GST‐NHE1.cd protein in the GST pull down assay, confirming the interaction in vitro. LDHB antibody immuno‐precipitated endogenous LDHB together with NHE1 from H9c2 cells, validating cellular interaction between NHE1 and LDHB. Subsequent analysis revealed that the overexpression of LDHB increased intracellular PH, implying opening of the NHE1 transporter. Moreover, overexpression of LDHB activated caspase 3 and induced cell death, consistent with the expected phenotype of hyper‐activation of NHE1. Collectively, our data indicate that LDHB modulates NHE1 activity via physical interaction.

이스트 two-hybrid 시스템을 이용한 hnRNP E1 cDNA의 클로닝과 hnRNP E1-hnRNP K 상호결합에 대한 연구

hnRNP K 단백질은 hnRNP 복합체를 구성하는 핵단백질들 중의 하나이며 시토신이 많은 RNA/DNA sequence에 잘 결합한다. 이 단백질은 핵 내에서만 머무르지 않고 핵과 세포질을 왕복하는 특징을 지니고 있다. hnRNP K의 기능을 조사하기 위하여 우선 hnRNP K와 상호 결합하는 세포내 단백질을 찾아내고자 하였다. 이를 위하여 본 연구에서는 이스트 two-hybrid 시스템을 사용하여 HeLa CDNA librar를 탐색하였다. 그 결과 얻은 클론들 중에는 사람의 hnRNP E1 (poly(rC) binding protein 1) cDNA (GenBank accession number XM_031585) 클론이 포함되어 있었다. 본 논문에서는 이스트 two-hybrid 시스템과 in vitro에서의 생화학적 실험을 통하여 hnRNP E1은 hnRNP K와 특이적으로 상호 결합한다는 것을 밝혔다. The heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a component of hnRNP complexes. This protein binds strongly to cytidine-rich RNA/DNA sequences. It is a nucleocytoplasmic shuttling protein. To investigate the functions of hnRNP K, I searched for hnRNP K-interacting proteins in HeLa cDNA library using a yeast two-hybrid screening system. One of the cDNA clones is identical to human hnRNP E1 (poly(rC) binding protein 1) cDNA (GenBank accession number XM_031585). In this study, hnRNP K is shown to specifically interact with hnRNP E1 in yeast two-hybrid system and in vitro biochemical assay.

Goodpasture Antigen-binding Protein and Its Spliced Variant, Ceramide Transfer Protein, Have Different Functions in the Modulation of Apoptosis during Zebrafish Development

Human Goodpasture antigen-binding protein (GPBP) is an atypical protein kinase that phosphorylates the Goodpasture auto-antigen, the alpha3 chain of collagen IV. The COL4A3BP gene is alternatively spliced producing two protein isoforms: GPBP and GPBPDelta26. The latter lacks a serine-rich domain composed of 26 amino acid residues. Both isoforms also function as ceramide transfer proteins (CERT). Here, we explored the function of Gpbp and GpbpDelta26/CERT during embryogenesis in zebrafish. We cloned both splice variants of the zebrafish gene and found that they are differentially expressed during development. We used antisense oligonucleotide-mediated loss-of-function and synthetic mRNA-based gain-of-function approaches. Our results show that the loss-of-function phenotype is linked to cell death, evident primarily in the muscle of the somites, extensive loss of myelinated tracks, and brain edema. These results indicate that disruption of the nonvesicular ceramide transport is detrimental to normal embryonic development of somites and brain because of increased apoptosis. Moreover, this phenotype is mediated by Gpbp but not GpbpDelta26/CERT, suggesting that Gpbp is an important factor for normal skeletal muscle and brain development.