Prolactin-Regulated Apoptosis of Nb2 Lymphoma Cells: pim-1 , bcl-2 , and bax Expression

Abstract

Lactogen-dependent Nb2 lymphoma cells, widely employed for studying prolactin (PRL) mitogenic mechanisms, are also useful for investigations of apoptosis in T-lineage lymphocytes. Utilizing PRL-dependent Nb2-11 cultures, apoptosis-regulatory genes were evaluated for participation in dexamethasone- (DEX) provoked cell death or its inhibition by PRL. Treatment of lactogen-starved, G1-arrested Nb2-11 cells with DEX (100 nM) activated apoptosis within 12 h evaluated by flow cytometric analysis of fragmented DNA. This effect was not associated with altered expression of bcl-2, bax, or pim-1. PRL (10 ng/mL), coincubated with DEX-treated cells, completely blocked DEX-induced apoptosis. This inhibition was associated with increased expression of bcl-2 and pim-1 mRNAs, genes reported to suppress apoptosis, within 2-6 h after addition of the hormone. Moreover, the increased transcription of bcl-2 and pim-1 was coupled to increases in their protein levels. The results suggest that bcl-2, bax, and pim-1 do not play a critical role in DEX-induced apoptosis in Nb2 cells. However, expression of bcl-2, together with pim-1, may have a role in mediating the antiapoptotic actions of PRL.

Human prolactin (hPRL) antagonists inhibit hPRL-activated signaling pathways involved in breast cancer cell proliferation

“…This result is diametrically opposed to our observations which clearly show that G129R-hPRL lacks signaling ability, whatever the molecular target analysed. Moreover, since hPRL has been shown to exert an anti-apoptotic role in lymphoid cells (Krumenacker et al, 1998) and potentially in mouse mammary cells (Gordon et al, 2000), this would imply that the hPRLR may transmit opposite signals depending on the ligand, which is very unlikely. On the other hand, the decrease of cell number observed by Chen et al (1999) in the presence of G129R-hPRL more probably re¯ects the competitive inhibition of the proliferative e ect exerted by endogenous hPRL, as previously observed using anti-hPRL antibodies (Ginsburg and Vonderhaar, 1995).…”

Prolactin gene-disruption arrests mammary gland development and retards T-antigen-induced tumor growth

“…An anti-apoptotic action of PRL in the tumors might also explain the increase in their overall growth rate. Whether PRL a ects apoptosis in mammary gland cells is not known, but PRL is a potent anti-apoptotic agent in Nb2 lymphoma cells (Krumenacker et al, 1998). Stat5a, which is activated in response to PRL, is antiapoptotic in mouse mammary glands (Li et al, 1997).…”

Regulation of bcl-2 gene expression in human breast cancer cells by prolactin and its antagonist, hPRL-G129R

“…There are numerous molecules that can regulate Bcl-2. For example, IL-3 has been shown to increase the expression of bcl-2 in hematopoietic cell lines (Krumenacker et al, 1998). Studies using Nb2 cells, a rat lymphoma cell line, show that bcl-2 is upregulated in immortalized cell lines (Krumenacker et al, 1998;Leff et al, 1996).…”

“…For example, IL-3 has been shown to increase the expression of bcl-2 in hematopoietic cell lines (Krumenacker et al, 1998). Studies using Nb2 cells, a rat lymphoma cell line, show that bcl-2 is upregulated in immortalized cell lines (Krumenacker et al, 1998;Leff et al, 1996). One of the more relevant studies involving bcl-2 demonstrated that treatment of Nb2 cells with PRL results in bcl-2 up-regulation and bax down-regulation (Krumenacker et al, 1998).…”

“…Studies using Nb2 cells, a rat lymphoma cell line, show that bcl-2 is upregulated in immortalized cell lines (Krumenacker et al, 1998;Leff et al, 1996). One of the more relevant studies involving bcl-2 demonstrated that treatment of Nb2 cells with PRL results in bcl-2 up-regulation and bax down-regulation (Krumenacker et al, 1998). However, there have been no definitive studies linking hPRL to Bcl-2 activity in human breast cancer cells.…”