Human Trop-2 is a tumor-associated calcium signal transducer.
Trop-2/EGP-1/GA733-1 is a recently identified cell surface glycoprotein highly expressed by human carcinomas. The cytoplasmic tail of Trop-2 possesses potential serine and tyrosine phosphorylation sites and a phosphatidyl-inositol binding consensus sequence. Thus, we investigated whether Trop-2 might be a functional signaling molecule. Using the fluorescent probe Fura-2, we assayed the cytoplasmic calcium levels in human cancer cells stimulated with anti-Trop-2 or control antibodies. Three anti-Trop-2 MAbs, Rs7-7G11, MOv16 and 162-46.2 specifically induced a transient intracellular calcium level increment in up to 40% of the experiments performed. Polyclonal antisera recognizing recombinant Trop-2 molecules possessed a much lower stimulation efficiency. The average latency of antibody-induced Ca2+ rise for OvCa-432 cells was 64+/-26 sec. Internal Ca2+ concentrations reached peaks of 190+/-24 nM vs. basal levels of 61+/-4 nM and returned to baseline within 193+/-37 sec. Similar values were obtained in MCF-7 cells. For comparison, stimulation of P2-purinergic receptors on MCF-7 and OvCa-432 cells induced a Ca2+ rise in most cases, leading to average internal Ca2+ concentrations of 297+/-41 and 391+/-39 nM, respectively. Our findings show that Trop-2 transduces an intracellular calcium signal, are consistent with the hypothesis that it acts as a cell surface receptor and support a search for a physiological ligand.
Ripani
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E
Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, Santa Maria Imbaro (Chieti), Italy.
Sacchetti
A
A
Corda
D
D
Alberti
S
S
D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000918:Antibody Specificity; D000951:Antigens, Neoplasm / Q000494:pharmacology / Q000502:physiology*; D000954:Antigens, Surface / Q000494:pharmacology / Q000502:physiology*; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules; D003600:Cytosol / Q000502:physiology; D000071858:Epithelial Cell Adhesion Molecule; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D018796:Immunoconjugates / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D010051:Ovarian Neoplasms / Q000378:metabolism* / Q000473:pathology; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D018796:Immunoconjugates; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D002118:Calcium