Human Insulinoma Hybrids Produce Proinsulin-like Material

We have established somatic cell hybrids by fusing cells from two human insulinomas with an established murine cell line LMTK⁻ CUD. After selection of the hybrids, the media were analyzed and found to contain insulin and human C-peptide immunoreactive material. The newly synthesized material was further characterized by pulse labeling and immunoprecipitation, and shown in five hybrid lines on Sephadex G-50 chroma-tography to have a size similar to proinsulin. The hybrids produced the apparent proinsulin-like material for up to 7 mo. Chromosome composition of the hybrids was determined by isozyme analysis and banding techniques. Chromosome 11, which previously has been assigned the insulin gene using cDNA probes, was identified in the hybrids producing proinsulin-like material. However, the retention of this chromosome did not always assure the production of hormone. This independent technique has confirmed the localization of the insulin gene to chromosome 11 and offers the opportunity of studying insulin processing and developing continuous insulin-producing cell lines.