Karyotypic changes associated with loss of prolactin dependency of rat Nb2 node lymphoma cell cultures

The parent line of cultured "Nb2 node" lymphoma cells is dependent on the hormone prolactin (PRL) for growth and is widely used for the in vitro bioassay of lactogenic hormones. As reported previously, PRL-independent sublines have been developed in vitro from the parental line by lactogen deprivation. The present study describes the G-banded karyotypes of the Noble (Nb) strain of rat (in which the original lymphoma developed), the PRL-dependent cell line (157th generation), and two of its PRL-independent sublines (1220th and 2372nd generations). The karyotype of the Nb rat was determined to be the same as that of Rattus norvegicus. The stemline karyotype of the PRL-dependent cells contains a number of well-defined chromosomal abnormalities. The PRL-independent sublines examined have the same chromosomal abnormalities as the PRL-dependent cells plus a few additional changes indicative of clonal evolution from the PRL-dependent stemline. The development of PRL independence (as seen in the 1220th generation) was associated with only two karyotypic changes, i.e., loss of the Y chromosome and a translocation involving chromosomes 14 and 17. The recently reported mapping of the rat PRL gene and other PRL-related genes to chromosome 17 suggests that rearrangement of chromosome 17 could be involved in the development of the PRL independence. The PRL-dependent and PRL-independent Nb2 cell lines provide a useful system for studying chromosomal and molecular genetic events associated with the malignant progression of polypeptide hormone-dependent cancers.