Monoclonal antibodies to alpha I spectrin Src homology 3 domain associate with macropinocytic vesicles in nonerythroid cells

Spectrins represent a family of membrane-associated proteins responsible fo r membrane flexibility and cell shape in erythrocytes, and probably in most nonerythroid cells. Spectrin functions as a tetramer consisting of two het erodimers each containing two subunits termed alpha and beta. In humans, al phaI and alpha II spectrins but not beta spectrins are characterized by the presence of an Src homology 3 (SH3) domain. As a tool to investigate the f unction of spectrin SH3 domains we derived several monoclonal antibodies (m Ab) to the recombinant human alphaI or alpha II spectrin SH3 domain. Immuno staining using these monoclonal antibodies indicated expression of alphaI s pectrin in cell bodies and alpha II spectrin in neurites of granule neurons in mouse primary cerebellar cultures. Monoclonal antibodies reactive to aI spectrin SH3 domain indicated expression of a protein(s) containing an alp haI-like SH3 domain in cytoplasmic vesicular-like structures in GFAP-positi ve cells in these cultures. In NIH 3T3 fibroblasts, these antibodies label macropinocytic vesicles. Together, these data and Western blotting results suggest expression of at least three spectrin-SH3 domain antibody-reactive proteins. (C) 2001 Elsevier Science B.V. All rights reserved.