Disease relevance of Gpa33

• We have developed an immunoblot method, based on nonreducing/non-urea precast 2-DE gels, that has facilitated the purification of the detergent (0.3% Triton X-100) solubilised A33 antigen from the human colon cancer cell lines LIM1215 and SW1222 [1].
• Similarity with recently described human cell surface molecules, A33 antigen and CAR (coxsackie and adenovirus 5 receptor), and a number of expressed sequence tags leads us to propose that CTX defines a novel subset of the Igsf, conserved throughout vertebrates and extending beyond the immune system [2].
• Encouraged by the success of the biodistribution and imaging characteristic studies performed at Memorial Sloan-Kettering Cancer Center by the New York Branch of the Ludwig Institute in colorectal cancers, a new clinical study of humanized monoclonal antibody huA33 against A33 antigen-positive gastric cancers has been initiated in Japan [3].

High impact information on Gpa33

• The A33 antigen is a transmembrane protein expressed almost exclusively by intestinal epithelial cells [4].
• Analysis of the regulation of the A33 antigen gene reveals intestine-specific mechanisms of gene expression [4].
• Thus, the A33 antigen has emerged as a definitive marker for all intestinal epithelial cells, irrespective of cell lineage and differentiation status [4].
• Explants taken from specific regions of the gut and placed into organ culture develop and express molecular markers (Cdx1, Cdx2 and A33 antigen) in the same spatial and temporal pattern observed in vivo indicating that regional specification is maintained [5].
• Using polyclonal antibodies raised against a synthetic peptide corresponding to the N-terminal region of the A33 antigen we have used Western blot analysis to localise the molecule in our master 2-DE protein database for normal human colon crypts and several colon carcinoma cell lines (URL address: http:(/)/www.ludwig.edu.au) [1].

Biological context of Gpa33

• During embryonic development, mA33 antigen expression is first observed in the inner cell mass of blastocysts before implantation [6].
• The onset of mA33 antigen expression in the gut occurs at the beginning of an extensive phase of cell movement involved in the conversion of the endoderm cell layer to a single cell layer of polarized epithelium [7].

Anatomical context of Gpa33

• Expression of mA33 antigen is then maintained into adulthood, where it is a definitive marker of intestinal epithelium [7].
• The A33 antigen is not secreted or shed and after mAb A33 binds to antigen on the cell membrane, a fraction of membrane-bound mAb A33 is internalized into endosomes [8].

Associations of Gpa33 with chemical compounds

• In this report we show that the A33 antigen is (I) N-glycosylated, containing approximately 8 K of N-linked carbohydrate and there is no evidence for O-glycosylation, sialylation or glycophosphatidylinositol, and (ii) S-acylated in vitro, incorporating [3H] palmitic acid linked through a hydroxylamine-sensitive thioester bond [9].

Analytical, diagnostic and therapeutic context of Gpa33

• Cloning and sequence determination of cDNAs encoding mA33 antigen predict a novel type 1 transmembrane protein of 298 amino acids, comprising an extracellular domain with two immunoglobulin-like domains, a single-span transmembrane domain, and a highly acidic cytoplasmic domain [6].
• The expression pattern of the murine A33 antigen has been defined during development using wholemount immunohistochemistry [7].
• Under these 2-DE conditions, the A33 antigen electrophoreses with an apparent M(r) approximately 41000 and pI 5.0-6 [1].
• However, using Western blot and biosensor detection the A33 antigen has been purified chromatographically and N-terminal sequence analysis was possible [1].
• There are several intestinal cell surface proteins such as the A33 antigen which have been used as targets for immunotherapy [10].

References