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α‐Adrenergic inhibition of proliferation in HepG2 cells stably transfected with the α 1B ‐adrenergic receptor through a p42 MAP kinase /p21 Cip1/WAF1 ‐dependent pathway
Author(s) -
Auer Kelly L,
Spector Mark S,
Tombes Robert M,
Seth Prem,
Fisher Paul B,
Gao Bin,
Dent Paul,
Kunos George
Publication year - 1998
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(98)01074-6
Subject(s) - transfection , cell growth , microbiology and biotechnology , phenylephrine , growth inhibition , biology , cell cycle , dna synthesis , kinase , recombinant dna , cell culture , cell , endocrinology , biochemistry , dna , gene , genetics , blood pressure
Activation of α 1B adrenergic receptors (α 1B AR) promotes DNA synthesis in primary cultures of hepatocytes, yet expression of α 1B AR in hepatocytes rapidly declines during proliferative events. HepG2 human hepatoma cells, which do not express α 1B AR, were stably transfected with a rat α 1B AR cDNA (TFG2 cells), in order to study the effects of maintained α 1B AR expression on hepatoma cell proliferation. TFG2 cells had a decreased rate of growth compared to mock transfected HepG2 cells as revealed by a decrease in [ 3 H]thymidine incorporation into DNA. Stimulation of α 1B AR with phenylephrine caused a further large reduction in TFG2 cell growth, whereas no effect on growth was observed in mock transfected cells. Reduced cell growth correlated with increased percentages of cells found in G 0 /G 1 and G 2 /M phases of the cell cycle. In TFG2 cells, phenylephrine increased p42 MAP kinase activity by 1.5‐ to 2.0‐fold for up to 24 h and increased expression of the cyclin dependent kinase inhibitor protein p21 Cip1/WAF1 . Treatment of TFG2 cells with the specific MEK1 inhibitor PD98059, or infection with a −/− MEK1 recombinant adenovirus permitted phenylephrine to increase rather than decrease [ 3 H]thymidine incorporation. In addition, inhibition of MAP kinase signaling by PD98059 or MEK1 −/− blunted the ability of phenylephrine to increase p21 Cip1/WAF1 expression. In agreement with a role for increased p21 Cip1/WAF1 expression in causing growth arrest, infection of TFG2 cells with a recombinant adenovirus to express antisense p21 Cip1/WAF1 mRNA blocked the ability of phenylephrine to increase p21 Cip1/WAF1 expression and to inhibit DNA synthesis. Antisense p21 Cip1/WAF1 permitted phenylephrine to stimulate DNA synthesis in TFG2 cells, and abrogated growth arrest. These results suggest that transformed hepatocytes may turn off the expression of α 1B ARs in order to prevent the activation of a growth inhibitory pathway. Activation of this inhibitory pathway via α 1B AR appears to be p42 MAP kinase and p21 Cip1/WAF1 dependent.