Stimulation of GRP78 gene transcription by phorbol ester and cAMP in GH3 pituitary cells. The accommodation of protein synthesis to chronic deprivation of intracellular sequestered calcium.
GRP78/BiP resides in the lumen of the endoplasmic reticulum (ER), a major site of Ca2+ sequestration and early protein processing. Agents, such as ionophore A23187, that mobilize sequestered ER Ca2+ suppress translational initiation within minutes and induce GRP78 within 1-3 h accompanied by development of translational tolerance to the inhibitor. Accommodation is prevented by actinomycin D and reduced by antisense oligonucleotides directed against GRP78 mRNA. In GH3 cells, optimal induction of GRP78 and translational accommodation depended on cAMP elevation and phorbol ester. GRP78 mRNA was induced 3-6-fold with A23187 alone as compared with 12-20-fold with ionophore plus cAMP-elevating agent and phorbol ester, but was not markedly induced without A23187. GRP78 gene transcription in nuclei isolated from A23187-treated cells was increased 2-4-fold by cAMP and phorbol ester. A nucleotide sequence homologous to the cAMP-responsive element consensus potentially exists in the promoter region of the GRP78 gene. GRP78 mRNA in ionophore-treated cells was largely associated with mono- and polysomal fractions rather than ribonuclear protein particles, a distribution different from actin and tubulin mRNAs. While polysomal content increased in cells undergoing translational recovery, cAMP and phorbol esters did not affect GRP78 mRNA stability. Translational accommodation in ionophore-treated GH3 cells is proposed to involve enhanced transcription of GRP78 mRNA promoted by cAMP/phorbol ester in conjunction with preferential polysomal loading of the message.
Prostko
C R
CR
Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854.
Brostrom
M A
MA
Galuska-Malara
E M
EM
Brostrom
C O
CO
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000737:chemistry; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*
D012333:RNA, Messenger; D000001:Calcimycin; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium