VASOPRESSIN MESSENGER-RNA AND NEUROPHYSIN-RELATED CELL-SURFACE ANTIGEN (NRSA) IN SMALL-CELL CARCINOMA

Production by small-cell carcinoma (SCCL) of neurophysins (HNPs) and neurophysin-related cell-surface antigen (NRSA) was examined for two cell lines, for mouse xenografts, and for a resected human tumor, using polyclonal and monoclonal antibodies to vasopressin-associated human neurophysin (VP-HNP) and polyclonal antibodies to vasopressin (VP). The nature of the mRNA responsible for giving rise to these neurophysin-related products was investigated by performing Northern analysis on preparations of poly A+ RNA with cDNA probes complimentary to portions of the exon A, exon B, and exon C regions of the human VP gene. SDS-electrophoresis and Western analysis revealed two prominent proteins of 42,000 and 20,000 Da in acid extracts from all SCCL sources when the monoclonal anti-HNP or one of the two polyclonal anti-HNP preparations were used. These antibodies also disclosed the presence of a minor component of 10,000 Da. A second polyclonal anti-HNP preparation reacted with one prominent protein of 30,000 Da and, for one cell line and mouse xenografts, another protein of 32,000 Da. Both of two anti-VP preparations reacted with proteins of 42,000, 30,000, 25,000, and 20,000 Da in extracts from all SCCL source material. The immunoreactive proteins of 42,000, 30,000, and 20,000 Da were all components of a membrane fraction from SCCL cells and tissues. In Northern analysis, a single RNA of about 900 bases hybridized with exon A and exon B probes, but not with the cDNA probe complimentary to exon C of the VP gene. These data demonstrate that large and heterogeneous forms of neurophysin are a common feature of SCCL production, and that at least three of these proteins contain a sequence for VP and may constitute NRSA. An abnormal VP mRNA of 900 bases seems to be responsible for the generation of these proteins. This tumor VP mRNA appears to differ from the neuronal form at its 3' end and could be the product of abnormal splicing.