Augmentation of ethanol-induced cell damage and activation of nuclear factor-kappa B by annexin IV in cultured cells

Highly pathogenic natural monoclonal antibody B4-IgM recognizes a post-translational modification comprised of acetylated N-terminal methionine followed by aspartic or glutamic acid

The natural monoclonal antibody B4-IgM recognizes murine annexin 4 (mAn4) and exacerbates ischemia-reperfusion injury in many mouse models. During apoptosis, the intracellular mAn4 protein translocates to the membrane surface, remaining attached to the outer membrane leaflet where it is recognized by the anti-mAn4 B4-IgM antibody. B4-IgM does not recognize human annexin 4 (hAn4). However, the B4-IgM antibody epitope was detected by Western blot of unknown human proteins and by flow cytometry on all studied human cell lines undergoing apoptosis and on a minor subset of healthy cells. The B4-IgM antibody also recognizes the epitope on necrotic cells in cytoplasmic proteins, apparently entering through pores large enough to allow natural antibodies to penetrate the cells and bind to the epitope expressed on self-proteins. Using proteomics and site-directed mutagenesis, we found that B4-IgM binds to an epitope with post-translationally modified acetylated N-terminal methionine, followed by either glutamic or aspartic acid. The epitope is not induced by apoptosis or injury because this modification can also occur during protein translation. This finding reveals an additional novel mechanism whereby injured cells are detected by natural antibodies that initiate pathogenic complement activation through the recognition of epitopes that are shared across multiple proteins found in variable cell lines.

Identification of Annexin A4 as a hepatopancreas factor involved in liver cell survival

To gain insight into liver and pancreas development, we investigated the target of 2F11, a monoclonal antibody of unknown antigen, widely used in zebrafish studies for labeling hepatopancreatic ducts. Utilizing mass spectrometry and in vivo assays, we determined the molecular target of 2F11 to be Annexin A4 (Anxa4), a calcium binding protein. We further found that in both zebrafish and mouse endoderm, Anxa4 is broadly expressed in the developing liver and pancreas, and later becomes more restricted to the hepatopancreatic ducts and pancreatic islets, including the insulin producing ß-cells. Although Anxa4 is a known target of several monogenic diabetes genes and its elevated expression is associated with chemoresistance in malignancy, its in vivo role is largely unexplored. Knockdown of Anxa4 in zebrafish leads to elevated expression of caspase 8 and Δ113p53, and liver bud specific activation of Caspase 3 and apoptosis. Mosaic knockdown reveal that Anxa4 is required cell-autonomously in the liver bud for cell survival. This finding is further corroborated with mosaic anxa4 knockout studies using the CRISPR/Cas9 system. Collectively, we identify Anxa4 as a new, evolutionarily conserved hepatopancreatic factor that is required in zebrafish for liver progenitor viability, through inhibition of the extrinsic apoptotic pathway. A role for Anxa4 in cell survival may have implications for the mechanism of diabetic ß-cell apoptosis and cancer cell chemoresistance.

Targeting annexin A4 to counteract chemoresistance in clear cell carcinoma of the ovary

IMPORTANCE OF THE FIELD

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecological malignancies in Western countries. Among the four major histological subtypes of EOC, clear cell carcinoma (CCC) of the ovary is highly resistant to platinum-based chemotherapy and is consequently associated with poor patient prognosis in advanced stages.

AREAS COVERED IN THIS REVIEW

An overview of the clinical characteristics of ovarian CCC; the role of annexin family proteins in tumor development and progression; the role of annexin A4 in enhancing cellular drug resistance; recent studies linking annexin A4 overexpression to chemoresistance in tumors of ovarian CCC.

WHAT THE READER WILL GAIN

Insight into the emerging role for annexin A4 in enhancing chemoresistance in ovarian CCC.

TAKE HOME MESSAGE

Annexin A4 enhances cancer cell chemoresistance and is overexpressed in tumors of patients with ovarian CCC. Targeting of annexin A4 may represent a future strategy to counteract resistance to chemotherapy in ovarian CCC.

Pathogenic natural antibodies recognizing annexin IV are required to develop intestinal ischemia-reperfusion injury

Intestinal ischemia-reperfusion (IR) injury is initiated when natural IgM Abs recognize neo-epitopes that are revealed on ischemic cells. The target molecules and mechanisms whereby these neo-epitopes become accessible to recognition are not well understood. Proposing that isolated intestinal epithelial cells (IEC) may carry IR-related neo-epitopes, we used in vitro IEC binding assays to screen hybridomas created from B cells of unmanipulated wild-type C57BL/6 mice. We identified a novel IgM mAb (mAb B4) that reacted with the surface of IEC by flow cytometric analysis and was alone capable of causing complement activation, neutrophil recruitment and intestinal injury in otherwise IR-resistant Rag1(-/-) mice. mAb B4 was found to specifically recognize mouse annexin IV. Preinjection of recombinant annexin IV blocked IR injury in wild-type C57BL/6 mice, demonstrating the requirement for recognition of this protein to develop IR injury in the context of a complex natural Ab repertoire. Humans were also found to exhibit IgM natural Abs that recognize annexin IV. These data in toto identify annexin IV as a key ischemia-related target Ag that is recognized by natural Abs in a pathologic process required in vivo to develop intestinal IR injury.

Partial hepatectomy induced liver proteome changes in mice

Acceleration of liver regeneration could be of great clinical benefit in various liver-associated diseases. However, at present little is known about therapeutic interventions to enhance this regenerative process. Our limited understanding and the complexity of the mechanisms involved have prevented the identification of new targets for treatment. Here we propose a broad-range proteomic approach to this problem that makes possible the simultaneous study of different signaling and metabolic pathways on the liver proteome. Changes in protein expression in mouse livers (n = 5 per group) at 6 h and 12 h after partial hepatectomy and sham operation, as compared to untreated controls, were analyzed using two-dimensional gel electrophoresis, mass spectrometry (MS), and mass fingerprinting. Twelve proteins, identified by MS, were up-regulated by at least 2-fold after partial hepatectomy. These included adipose differentiation-related protein, gamma-actin, enoyl coenzyme A hydratase 1, serum amyloid A and eukaryotic translation initiation factor 3. These results indicate that liver regeneration following partial hepatectomy affects various signaling and metabolic pathways.