Nb2 cell proliferation

The Nb2 cell line was derived from a rat lymphoma and can be grown in vitro indefinitely. Its growth is dependent on the presence of serum in particular, in the presence of 10% horse serum and 10% fetal calf serum, proliferation of Nb2 cells is rapid, but if the fetal calf serum is omitted proliferation almost ceases. A series of studies showed that the requirement for fetal calf serum could be replaced by prolactin or other lactogenic hormones (human GH has frequently been used) [105], It is not clear that the component in fetal calf serum that provides the stimulant for growth of the cell line actually is prolactin [106], but it is established that under appropriate conditions (presence of horse serum) lactogenic hormones act as specific mitogens for the line (Fig. 8). The response is very sensitive, 1 ng/ml giving a max- 

The nature of the second messenger(s) involved in the action of prolactin on Nb2 cells has been studied [108]. Levels of intracellular cyclic AMP do not change when the cells are treated with prolactin, and cyclic AMP analogues and phosphodiesterase inhibitors do not induce proliferation. Similarly, no clear evidence could be obtained for a clear-cut involvement of prostaglandins in Nb2 cell proliferation. 

A possible involvement of polyamines in the response has been suggested. Prolactin stimulated ornithine decarboxylase activity in Nb2 cells [109]. A specific inhibitor of this enzyme partially blocked the actions of lactogenic hormones on Nb2 cell proliferation [110], and addition of polyamines (putrescine, spermidine or spermine) restored normal growth. However, polyamines alone had no effect on Nb2 cell proliferation, suggesting that they are not the sole or major factors involved in mediating the actions of prolactin on cell growth. 

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Lebrun, J. J., Ali, S., Sofer, L., Ullrich, A., and Kelly, P. A. (1994). Prolactin-induced proliferation of Nb2 cells involves tyrosine phosphorylation of the prolactin receptor and its associated tyrosine kinase JAK2./. Biol. Chem. 269, 14021-14026. 

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