Clonal derivatives of a human B-lymphoblastoid cell line producing prolactin--a cytogenetic characterization.

The IM-9-P cell line is a variant of the human B-lymphoblastoid cell line IM-9 which ectopically secretes prolactin (hPRL). The heterogeneous line IM-9-P and three sublines of clonal origin, two of them positive and one negative for PRL gene expression, were subjected to cytogenetic analysis and compared with the reference line IM-9 which showed a normal female diploid karyotype. G-banding revealed several rearrangements in the chromosomes. Nine altered chromosomes including one stable marker chromosome were common to all analysed karyotypes of IM-9-P cells and their clones. A second marker chromosome 'mar2' occurred only in the karyotypes of the hPRL producing clones, but not in the non-producing clone. None of the visible alterations involve chromosome 6 which carries the PRL gene in humans.