Among circulating hematopoietic cells, B-CLL uniquely expresses functional EPAC1, but EPAC1-mediated Rap1 activation does not account for PDE4 inhibitor-induced apoptosis

Blood. 2004 Apr 1;103(7):2661-7. doi: 10.1182/blood-2003-06-2154. Epub 2003 Nov 13.

Abstract

Type 4 cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE4) inhibitors and other agents that raise intracellular cAMP levels induce apoptosis in B-cell chronic lymphocytic leukemia (B-CLL) but not in T-CLL or peripheral blood T cells. Two principal effector proteins for cAMP are protein kinase A (PKA) and EPAC (exchange protein directly activated by cAMP), a Rap guanosine 5'-diphosphate (GDP) exchange factor. We here examine whether varying expression of EPAC accounts for the discrepant sensitivity of B-CLL and T cells to PDE4 inhibitor-induced apoptosis. B-CLL and peripheral blood B cells express EPAC1 transcript, whereas T-CLL, peripheral blood T cells, monocytes, and neutrophils do not. Treatment with the PDE4 inhibitor rolipram induces Rap1 activation in B-CLL cells but not in peripheral blood B cells, T-CLL, or any of the normal hematopoietic lineages examined. The EPAC-specific cAMP analog 8CPT-2Me-cAMP (8-(4-chloro-phenylthio)-2'-O-methyladenosine-3',5'-cAMP) activates Rap1 in B-CLL cells, but, unlike rolipram/forskolin or 8-Bromo-cAMP, it does not induce PKA activation, as judged by phosphorylation of the transcription factor cAMP-response element binding protein (CREB). Unexpectedly, whereas rolipram/forskolin and 8-Bromo-cAMP induce apoptosis in B-CLL cells, 8CPT-2Me-cAMP decreased basal apoptosis in B-CLL cells by an average of 25% (P<.002). Our results demonstrate that B-CLL cells uniquely activate Rap1 in response to PDE4 inhibitors and suggest that physiologic stimuli that activate EPAC may transmit an antiapoptotic signal.

Publication types

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

MeSH terms

  • 3',5'-Cyclic-AMP Phosphodiesterases / antagonists & inhibitors*
  • Apoptosis / drug effects*
  • B-Lymphocytes / immunology
  • Benzimidazoles / pharmacology
  • Colforsin / pharmacology
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cyclic Nucleotide Phosphodiesterases, Type 4
  • Enzyme Inhibitors / pharmacology*
  • Fluorescent Dyes
  • Guanine Nucleotide Exchange Factors / genetics*
  • Guanine Nucleotide Exchange Factors / metabolism
  • Humans
  • Leukemia, Lymphocytic, Chronic, B-Cell / physiopathology*
  • Leukocytes, Mononuclear / physiology
  • Monocytes / immunology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Rolipram / pharmacology
  • T-Lymphocytes / immunology
  • rap1 GTP-Binding Proteins / metabolism*

Substances

  • Benzimidazoles
  • Enzyme Inhibitors
  • Fluorescent Dyes
  • Guanine Nucleotide Exchange Factors
  • RAPGEF3 protein, human
  • Colforsin
  • Cyclic AMP-Dependent Protein Kinases
  • 3',5'-Cyclic-AMP Phosphodiesterases
  • Cyclic Nucleotide Phosphodiesterases, Type 4
  • rap1 GTP-Binding Proteins
  • Rolipram
  • bisbenzimide ethoxide trihydrochloride