Submitted on June 24, 2004
Accepted on July 24, 2004
Parathyroid Hormone-Related Protein Regulates Apoptosis in Lung Cancer Cells through Protein Kinase A
Randolph H Hastings1*, Flavio Araiza2, Douglas W Burton3, Maxwell Bedley2, and Leonard J Deftos3
1 Research, VA San Diego Healthcare System, San Diego, CA, USA; Anesthesiology, VA San Diego Healthcare System, San Diego, CA, USA; Anesthesiology, University of California, San Diego, La Jolla, CA, USA
2 Research, VA San Diego Healthcare System, San Diego, CA, USA
3 Research, VA San Diego Healthcare System, San Diego, CA, USA; Medicine Services, VA San Diego Healthcare System, San Diego, CA, USA; Medicine, University of California, San Diego, La Jolla, CA, USA
* To whom correspondence should be addressed. E-mail: rhhastings{at}ucsd.edu.
Parathyroid hormone-related protein (PTHrP) 1-34 and PTHrP 140-173 protect lung cancer cells from apoptosis after UV-irradiation. This study evaluated upstream signaling in PTHrPmediated alteration of lung cancer cell sensitivity to apoptosis. The two peptides increased cAMP levels in BEN lung cancer cells by 15-35% in 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, isobutylmethylxanthine or chlorophenylthio-cAMP
attenuated and H89 augmented apoptosis after UV exposure as indicated by caspase 3 activation, cell DNA loss, and morphologic 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 UVinduced 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.
