Sarcoplasmic reticulum Ca(2+) pump mRNA stability in cardiac and smooth muscle: role of the 3'-untranslated region.
Stomach smooth muscle (SSM) and left ventricular muscle (LVM) express the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pump gene SERCA2. Alternative splicing yields two major isoforms, SERCA2a in LVM and slow twitch muscle and SERCA2b in SSM and most other tissues. The splices have different 3'-untranslated regions (UTR) and also encode proteins that differ slightly in their COOH-terminal domains. SERCA2 transcription rates are similar in the two tissues, yet LVM has a much higher level of SERCA2 mRNA than SSM. To understand the control of SERCA2 RNA expression, we inhibited transcription and showed that the half-life of SERCA2 mRNA is significantly longer (P < 0.05) in primary cultures of LVM cells than in SSM cells. Nuclear SERCA2 mRNA levels were also higher in LVM than in SSM. In vitro decay assays using synthetic RNA corresponding to the 3'-UTR of SERCA2a and -2b showed that nuclear extracts produced a faster decay of SERCA2 RNA than cytoplasmic extracts and that nuclear extracts produced a faster decay of SERCA2b than -2a. This was also true when the full-length native mRNA was used instead of the 3'-UTR RNA, and SERCA2b decay by cytoplasmic extracts was faster for LVM than for SSM. We propose that nuclear decay is an initial step in the control of SERCA2 RNA abundance and that this control is maintained or modulated in the cytoplasm. We discuss how these control mechanisms may be part of a control switch in cardiac development and pathophysiology.
Misquitta
Christine M
CM
Department of Biology, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
Mwanjewe
James
J
Nie
Lin
L
Grover
Ashok K
AK
D020413:3' Untranslated Regions / Q000502:physiology*; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000235:genetics*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D006352:Heart Ventricles; D009130:Muscle, Smooth / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D020413:3' Untranslated Regions; D012333:RNA, Messenger; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases