Prolactin signaling to pim-1 expression: a role for phosphatidylinositol 3-kinase

Sublines of the lactogen-dependent, rat pre-T Nb2 lymphoma are useful as a model for the investigation of prolactin (PRL) signaling mechanisms, regula tion of transcription of target genes, and the immunomodulatory and anti-ap optotic actions of the hormone in T lymphocytes. In the present study, coup ling of various tyrosine, serine/threonine, and phospholipid kinase signali ng mechanisms to PRL-stimulated Nb2-11 cell proliferation and expression of the protooncogene, pim-1, was investigated utilizing pharmacologic antagon ists of a broad spectrum of tyrosine kinases (tyrphostin A25), and the spec ific enzymes, Jak2 (tyrphostin B42) and ZAP-70 (piceatannol), as well as mi togen-activated protein kinase (MAPK, PD98059), protein kinase C (PKC, calp hostin C), and phosphatidylinositol 3-kinase (PI3-kinase, LY294002). Inhibi tion of each pathway attenuated PRL-stimulated Nb2-11 cell proliferation in a concentration-dependent manner. Blockade of MAPK was the least efficacio us; it inhibited proliferation maximally by 60%. Northern blot analysis of pim-1 expression in antagonist-treated cells revealed that MAPK, Jak2 and P I3-kinase appeared to signal to initiation of pim-1 transcription; its expr ession was attenuated by each of the antagonists. In other experiments, PRL was shown to rapidly activate a downstream effector of PI3-kinase, Akt, an d this effect was also blocked by LY294002. It is concluded that PRL-stimul ated Nb2 cell proliferation requires participation of each of the signaling pathways investigated. Moreover, hormone-meduated expression of pim-1 appe ars to reflect signaling by MAPK, Jak2, and PI3-kinase. (C) 2001 Elsevier S cience B.V. All rights reserved.