Increase of Intracellular Cyclic AMP by PDE4 Inhibitors Affects HepG2 Cell Cycle Progression and Survival

Abstract

Type 4 cyclic nucleotide phosphodiesterases (PDE4) are major members of a superfamily of enzymes (PDE) involved in modulation of intracellular signaling mediated by cAMP. Broadly expressed in most human tissues and present in large amounts in the liver, PDEs have in the last decade been key therapeutic targets for several inflammatory diseases. Recently, a significant body of work has underscored their involvement in different kinds of cancer, but with no attention paid to liver cancer. The present study investigated the effects of two PDE4 inhibitors, rolipram and DC-TA-46, on the growth of human hepatoma HepG2 cells. Treatment with these inhibitors caused a marked increase of intracellular cAMP level and a dose- and time-dependent effect on cell growth. The concentrations of inhibitors that halved cell proliferation to about 50% were used for cell cycle experiments. Rolipram (10 μM) and DC-TA-46 (0.5 μM) produced a decrease of cyclin expression, in particular of cyclin A, as well as an increase in p21, p27 and p53, as evaluated by Western blot analysis. Changes in the intracellular localization of cyclin D1 were also observed after treatments. In addition, both inhibitors caused apoptosis, as demonstrated by an Annexin-V cytofluorimetric assay and analysis of caspase-3/7 activity. Results demonstrated that treatment with PDE4 inhibitors affected HepG2 cell cycle and survival, suggesting that they might be useful as potential adjuvant, chemotherapeutic or chemopreventive agents in hepatocellular carcinoma. J. Cell. Biochem. 118: 1401-1411, 2017. © 2016 Wiley Periodicals, Inc.

Role of cAMP and phosphodiesterase signaling in liver health and disease

“…This, in turn, led to de-phosphorylation of the signal transducer and activator of transcription 3 (STAT3) resulting in repressed STAT3 target genes and inhibition of hepatocarcinogenesis. Additionally, another study utilizing PDE4 inhibitors to increase intracellular cAMP levels reported that cAMP interfered with cell cycle progression (decreased availability of cyclin A and increased expression of p21) and inhibited cell proliferation in a hepatocarcinoma-derived cell line (HepG2 cells) [119]. …”

Human hepatocellular carcinoma: Protection by melatonin

“…Melatonin (2.5 mM) incubation of HepG2 cells could reduce cAMP level that further counteracted using luzindole (Carbajo‐Pescador et al, ), thereby suppression of MT1 receptor prevents cytotoxic and cytostatic effects of melatonin on HepG2 cells, possibly contributed to alterations in the intracellular concentrations of cAMP (Ordoñez et al, ). CAMP is also inhibited by type 4 cyclic nucleotide phosphodiesterases (PDE4) that is a main member of a superfamily of enzymes (PDE) responsible for inhibition of cAMP, p27 kip1 , p21, and p53 (Massimi et al, ). P27 is contributed to inhibition of cell cycle progression from G0 to G1 by regulating cdk2‐cyclin complex (cyclin A) (Massimi et al, ).…”

“…CAMP is also inhibited by type 4 cyclic nucleotide phosphodiesterases (PDE4) that is a main member of a superfamily of enzymes (PDE) responsible for inhibition of cAMP, p27 kip1 , p21, and p53 (Massimi et al, ). P27 is contributed to inhibition of cell cycle progression from G0 to G1 by regulating cdk2‐cyclin complex (cyclin A) (Massimi et al, ). As it has been previously discussed, melatonin is capable of inhibiting cell arrest in the G0/G1 phase of cell cycle (Carbajo‐Pescador et al, ) and increasing the rate for expressions of p21 (Carbajo‐Pescador et al, ) and p53 (Martín‐Renedo et al, ) (Figure ), so it seems that this indoleamine possibly regulates most of the functions for PDE4 in HepG2 cells.…”

Insights for the Inhibition of Cancer Progression: Revisiting Ca2+ and Camp Signalling Pathways

“…Thus, whether this interaction may be a novel therapeutic target to alter cancer tumor growth, angiogenesis and metastasis, without affecting normal cell physiology deserves special attention. Then, it would not be a surprise the suggestion of using CCBs in combination with pharmaceuticals which increase cAMP to inhibit cancer progression [8,9,15]. Therefore, the current knowledge about regulation of intracellular Ca 2+ and cAMP homeostasis in cancer tumor cells, and the search for new pharmacological strategies to control these intracellular messengers may be able to lead the development of new pharmacological and non-pharmacological strategies that specifically alter tumor growth, angiogenesis and metastasis, without affecting normal cell physiology.…”

“…In addition to Ca 2+ , cAMP has been implicated in the regulation of cancer progression [15]. From this concept in mind, phosphodiesterase IV inhibitors like rolipram, which increase cAMP have been proposed as potential adjuvant, chemotherapeutic or chemopreventive agents in hepatocellular carcinoma [15].…”