Rapid modulation of the apoptosis regulatory genes, bcl-2 and bax by prolactin in rat Nb2 lymphoma cells

Endocrinology. 1996 Dec;137(12):5456-62. doi: 10.1210/endo.137.12.8940371.

Abstract

The Nb2 rat lymphoma represents a useful model for investigation of molecular events coupled to PRL-induced proliferation. Moreover, recent evidence has also demonstrated the utility of this system to study mechanisms linked to programmed cell death (apoptosis). Thus, glucocorticosteroids activate apoptosis in lactogen-dependent Nb2 cells, whereas the addition of PRL abrogates this effect. The present study was conducted to determine whether PRL stimulation in lactogen-dependent Nb2-11 or autonomous Nb2-SFJCD1 cultures alters expression of bcl-2 or bax, genes that suppress or facilitate apoptosis, respectively. We demonstrate that PRL stimulation in stationary Nb2-11 cultures significantly increased the level of bcl-2 messenger RNA (mRNA) within 3 h (15-fold) and its protein product by 6 h, time points previously shown to correspond with G1 cell cycle progression. In Nb2-SFJCD1 cells, bcl-2 mRNA was found to be constitutively present. Addition of PRL to these lactogen-independent cultures further enhanced its expression at the mRNA and protein levels with a kinetic pattern similar to that observed in the PRL-dependent line. Results from stability studies indicated that increased bcl-2 mRNA evoked by PRL in Nb2 cell lines was most likely not attributable to increased stability of its transcripts. Furthermore, the rapid increase in its expression in PRL-stimulated Nb2-11 cells was not altered by inhibition of protein synthesis suggesting a direct action of the hormone. PRL also increased bax mRNA by 8 h in Nb2-11 cultures. However, hormone stimulation markedly attenuated the level of the Bax protein from 2-6 h. In contrast, bax expression in Nb2-SFJCD1 cultures remained unaltered by the addition of the hormone. These results demonstrate that altered expression of bcl-2 and bax are each associated with PRL-stimulated cell cycle progression in Nb2 cells. Moreover, bcl-2 appears to be an immediate-early gene induced by PRL in the hormone-dependent line and may represent an important regulator of early G1 cell cycle progression most likely by suppressing cell death mechanisms.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apoptosis / physiology*
  • Cycloheximide / pharmacology
  • Drug Stability
  • Gene Expression / drug effects*
  • Genes, Regulator*
  • Genes, bcl-2*
  • Humans
  • Lymphoma / genetics
  • Lymphoma / pathology
  • Mice
  • Prolactin / pharmacology*
  • Protein Synthesis Inhibitors / pharmacology
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins c-bcl-2*
  • RNA, Messenger / chemistry
  • RNA, Messenger / metabolism
  • Rats
  • Time Factors
  • Tumor Cells, Cultured
  • bcl-2-Associated X Protein

Substances

  • BAX protein, human
  • Bax protein, mouse
  • Bax protein, rat
  • Protein Synthesis Inhibitors
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Messenger
  • bcl-2-Associated X Protein
  • Prolactin
  • Cycloheximide