Parathyroid hormone-related protein regulates apoptosis in lung cancer cells through protein kinase A.
Parathyroid hormone-related protein (PTHrP)-(1-34) and PTHrP-(140-173) protect lung cancer cells from apoptosis after ultraviolet (UV) irradiation. This study evaluated upstream signaling in PTHrP-mediated alteration of lung cancer cell sensitivity to apoptosis. The two peptides increased cAMP levels in BEN lung cancer cells by 15-35% in a dose-dependent fashion, suggesting signaling through protein kinase A (PKA). In line with this view, the PKA inhibitor H89 abrogated the protective effects of PTHrP-(1-34) and PTHrP-(140-173) against caspase activation and DNA loss. PKA activation by forskolin, 3-isobutyl-1-methylxanthine (IBMX), or 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate attenuated and H89 augmented apoptosis after UV exposure as indicated by caspase-3 activation, cell DNA loss, and morphological criteria. Studies with IBMX and varying doses of forskolin indicated that small increases in cAMP, on the order of those generated by IBMX alone and the PTHrP peptides, were sufficient to protect lung cancer cells from apoptosis. In summary, PTHrP-(1-34) and PTHrP-(140-173) stimulate PKA in lung carcinoma cells and protect cells against UV-induced caspase-3 activation and DNA fragmentation. PKA activation by other means also induces resistance to apoptosis, and the protective effect of the PTHrP peptide is blocked by PKA inhibition. Thus PKA appears to have a role in the regulatory effects of PTHrP on lung cancer cell survival.
Hastings
Randolph H
RH
VA Medical Center (125), 3350 La Jolla Village Dr., San Diego, CA 92161-5085, USA. rhhastings@ucsd.edu
Araiza
Flavio
F
Burton
Douglas W
DW
Bedley
Maxwell
M
Deftos
Leonard J
LJ
D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053938:DNA Fragmentation / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D008175:Lung Neoplasms; D018307:Neoplasms, Squamous Cell; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism* / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology; D014466:Ultraviolet Rays
D007546:Isoquinolines; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C054296:parathyroid hormone-related protein (1-34); D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D020169:Caspases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide