title: Parathyroid-hormone-related protein signaling mechanisms in lung carcinoma growth inhibition.
abstract: Parathyroid hormone-related protein (PTHrP) inhibits proliferation of several lung cancer cell lines, but the signaling mechanism has not been established. This study tested the hypotheses that growth inhibition is mediated through the PTHrP receptor, PTH1R, and that the process is modified by ERK activation. PTHrP-positive and negative clones of H1944 lung adenocarcinoma cells underwent stable PTH1R knockdown with lentiviral shRNA or transient transfection with ERK1 and ERK2 siRNA. Alternatively, cells were treated with 8-CPT cAMP, 8-CPT 2'-O-methyl cAMP, and N-6-phenyl cAMP analogs. H1944 cells expressing ectopic PTHrP showed 20-40% decrease in proliferation compared to the PTHrP-negative cells in the presence of normal levels of PTH1R (P < 0.01). PTH1R knockdown eliminated this difference and increased cell proliferation regardless of PTHrP status. The three cAMP analogs each inhibited proliferation over 5 days by 30-40%. ERK2 knockdown inhibited proliferation of PTHrP-positive cells alone and in combination with ERK1 knockdown. The growth inhibition mediated by cAMP analogs was unaffected by ERK1 knockdown. In conclusion, ectopic expression of PTHrP 1-87 inhibits H1944 cell proliferation. PTH1R knockdown blocks this effect and stimulates proliferation, indicating that the ligand exerts anti-mitogenic effects. cAMP, the second messenger for PTH1R also inhibits proliferation and activates ERK. PTHrP growth inhibition may be opposed by concomitant ERK activation.
authors.affiliation: Medicine Service, Pulmonary and Critical Care Division, Department of Medicine, VA San Diego Healthcare System, UC San Diego, San Diego, USA.
authors.forename: Philippe R
authors.initials: PR
authors.lastname: Montgrain
authors.affiliation: Research Service, Department of Biology, VA San Diego Healthcare System, UC San Diego, San Diego, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Phun
authors.affiliation: Research Service, Department of Biology, VA San Diego Healthcare System, UC San Diego, San Diego, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Vander Werff
authors.affiliation: Research Service, VA San Diego Healthcare System, San Diego, USA.
authors.forename: Rick A
authors.initials: RA
authors.lastname: Quintana
authors.affiliation: Research Service, VA San Diego Healthcare System, San Diego, USA.
authors.forename: Ariea J
authors.initials: AJ
authors.lastname: Davani
authors.affiliation: Anesthesiology Service, Department of Anesthesiology, VA Medical Center (125), VA San Diego Healthcare System, UC San Diego, 3350 La Jolla Village Dr., San Diego, CA 92161 USA.
authors.forename: Randolph H
authors.initials: RH
authors.lastname: Hastings
keywords: Cell proliferation; Extracellular signal-related MAP kinases; Lung adenocarcinoma; Type 1 parathyroid hormone receptor