Neuroblastoma Differentiation Involves the Expression of Two Isoforms of the α‐Subunit of Go

Abstract

The regulation of GTP-binding proteins (G proteins) was examined during the course of differentiation of neuroblastoma N1E-115 cells. N1E-115 cell membranes possess three Bordetella pertussis toxin (PTX) substrates assigned to .alpha.-subunits (G.alpha.) of Go (a G protein of unknown function) and "Gi (a G protein inhibitory to adenylate cyclase)-like" proteins and one substrate of Vibrio cholerae toxin corresponding to an .alpha.-subunit of Gs (a G protein stimulatory to adenylate cyclase). In undifferentiated cells, only one form of Go.alpha. was found, having a pI of 5.8. Go.alpha. content increased by approximately twofold from the undifferentiated state to 96 h of cell differentiation. This is mainly due to the appearance of another Go.alpha. form having a pI of 5.55. Both Go.alpha. isoforms have similar sizes on sodium dodecyl sulfate-polyacrylamide gels, are recognized by polyclonal antibodies to bovine brain Go.alpha., are ADP-ribosylated by PTX, and are covalently myristylated in whole N1E-115 cells. In addition, immunofluorescent staining of N1E-115 cells with Go.alpha. antibodies revealed that association of Go.alpha. with the plasma membrane appears to coincide with the expression of the most acidic isoform and morphological cell differentiation. In contrast, the levels of both Gi.alpha. and Gs.alpha. did not significantly change, whereas that of the common .beta.-subunit increased by .apprx. 30% over the same period. These results demonstrate specific regulation of the expression of Go.alpha. during neuronal differentiation.