Chronic stress targets posttranscriptional mechanisms to rapidly upregulate α1C-subunit of Cav1.2b calcium channels in colonic smooth muscle cells

Qingjie Li, Sushil K. Sarna

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

Chronic stress elevates plasma norepinephrine, which enhances expression of the α1C-subunit of Cav1.2b channels in colonic smooth muscle cells within 1 h. Transcriptional upregulation usually does not explain such rapid protein synthesis. We investigated whether chronic stress-induced release of norepinephrine utilizes posttranscriptional mechanisms to enhance the α1C-subunit. We performed experiments on colonic circular smooth muscle strips and in conscious rats, using a 9-day chronic intermittent stress protocol. Incubation of rat colonic muscularis externa with norepinephrine enhanced α1C-protein expression within 45 min, without a concomitant increase in α1C mRNA, indicating posttranscriptional regulation of α1C-protein by norepinephrine. We found that norepinephrine activates the PI3K/Akt/GSK-3β pathway to concurrently enhance α1C-protein translation and block its polyubiquitination and proteasomal degradation. Incubation of colonic muscularis externa with norepinephrine or LiCl, which inhibits GSK-3β, enhanced p-GSK-3β and α1C-protein time dependently. Using enrichment of phosphoproteins and ubiquitinated proteins, we found that both norepinephrine and LiCl decrease α1C phosphorylation and polyubiquitination. Concurrently, they suppress eIF2α (Ser51) phosphorylation and 4E-BP1 expression, which stimulates gene-specific translation. The antagonism of two upstream kinases, PI3K and Akt, inhibits the induction of α1C-protein by norepinephrine. Cyanopindolol (β3-AR-antagonist) almost completely suppresses and propranolol (β1/2-AR antagonist) partially suppresses norepinephrine-induced α1C-protein expression, whereas phentolamine and prazosin (α-AR and α1-AR antagonist, respectively) have no significant effect. Experiments in conscious animals showed that chronic stress activates the PI3K/Akt/GSK-3β signaling. We conclude that norepinephrine released by chronic stress rapidly enhances the protein expression of α1C-subunit of Cav1.2b channels by concurrently suppressing its degradation and enhancing translation of existing transcripts to maintain homeostasis.

Original languageEnglish (US)
Pages (from-to)G154-G163
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume300
Issue number1
DOIs
StatePublished - Jan 1 2011

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Keywords

  • GSK-3
  • Irritable bowel syndrome
  • Posttranslational regulation
  • Wnt signaling

ASJC Scopus subject areas

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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