IP(3), IP(3) receptor, and cellular senescence.
Herein we demonstrate that replicative cellular senescence in vitro results in sharply reduced inositol 1,4,5-trisphosphate (IP(3)) receptor levels, reduced mitogen-evoked IP(3) formation and Ca(2+) release, and Ca(2+) store depletion. Human diploid fibroblasts (HDFs) underwent either 30 mean population doublings [mean population doublings (MPDs) thymidine labeling index (TI) >92% ("young") or between 53 and 58 MPDs (TI < 28%; "senescent")]. We found that the cytosolic Ca(2+) release triggered by either ionomycin or by several IP(3)-generating mitogens, namely bradykinin, thrombin, platelet-derived growth factor (PDGF), and epidermal growth factor (EGF), was attenuated markedly in senescent HDFs. Notably, the triggered cytosolic Ca(2+) transients were of a smaller magnitude in senescent HDFs. However, the response latency seen with both PDGF and EGF was greater for senescent cells. Finally, a smaller proportion of senescent HDFs showed oscillations. In parallel, IP(3) formation in response to bradykinin or EGF was also attenuated in senescent HDFs. Furthermore, senescent HDFs displayed a sharply diminished Ca(2+) release response to intracellularly applied IP(3). Finally, to compare IP(3) receptor protein levels directly in young and senescent HDFs, their microsomal membranes were probed in Western blots with a highly specific anti-IP(3) receptor antiserum, Ab(40). A approximately 260-kDa band corresponding to the IP(3) receptor protein was noted; its intensity was reduced by approximately 50% in senescent cells. Thus, we suggest that reduced IP(3) receptor expression, lowered IP(3) formation, and Ca(2+) release, as well as Ca(2+) store depletion, all contribute to the deficient Ca(2+) signaling seen in HDFs undergoing replicative senescence.
Huang
M S
MS
University of Arkansas for Medical Sciences and Veterans Affairs Geriatrics Research, Education, and Clinical Center, Little Rock, Arkansas 72205, USA.
Adebanjo
O A
OA
Awumey
E
E
Biswas
G
G
Koval
A
A
Sodam
B R
BR
Sun
L
L
Moonga
B S
BS
Epstein
J
J
Goldstein
S
S
Lai
F A
FA
Lipschitz
D
D
Zaidi
M
M
D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology; D002648:Child; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008934:Mitogens / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D015220:Calcium Channels; D006133:Growth Substances; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008934:Mitogens; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; D013917:Thrombin; D001920:Bradykinin; D002118:Calcium