Cell cycle actions of parathyroid hormone-related protein in non-small cell lung carcinoma

Abstract

Parathyroid hormone-related protein (PTHrP), a paraneoplastic protein expressed by two-thirds of human non-small cell lung cancers, has been reported to slow progression of lung carcinomas in mouse models and to lengthen survival of patients with lung cancer. This study investigated the effects of ectopic expression of PTHrP on proliferation and cell cycle progression of two human lung adenocarcinoma cell lines that are normally PTHrP negative. Stable transfection with PTHrP decreased H1944 cell DNA synthesis, measured by thymidine incorporation, bromodeoxyuridine uptake, and MTT proliferation assay. A substantial fraction of PTHrP-positive cells was arrested in or slowly progressing through G1. Cyclin D2 and cyclin A2 protein levels were 60-70% lower in PTHrP-expressing cells compared with control cells (P < 0.05, N = 3 independent clones per group), while expression of p27(Kip1), a cyclin-dependent kinase inhibitor, was increased by 35 +/- 9% (mean +/- SE, P < 0.05) in the presence of PTHrP. Expression of other cyclins, including cyclins D1 and D3, and cyclin-dependent kinases was unaffected by PTHrP. PTHrP did not alter the phosphorylation state of Rb, but decreased cyclin-dependent kinase (CDK) 2-cyclin A2 complex formation. Ectopic expression of PTHrP stimulated ERK phosphorylation. In MV522 cells, PTHrP had similar effects on DNA synthesis, cyclin A2 expression, pRb levels, CDK2-cyclin A2 association, and ERK activation. In summary, PTHrP appears to slow progression of lung cancer cells into S phase, possibly by decreasing activation of CDK2. Slower cancer cell proliferation could contribute to slower tumor progression and increased survival of patients with PTHrP-positive lung cancer.

Parathyroid-hormone-related protein signaling mechanisms in lung carcinoma growth inhibition

“…Similar to our 2009 findings (Hastings et al 2009), PTHrP-positive H1944 cells demonstrated pERK1 and pERK2 levels roughly twice as great as those in PTHrP-negative cells (Figure 3a). Total ERK protein expression was not altered significantly by PTHrP, based on immunoblotting.…”

“…Exogenous PTHrP inhibited wild type H1944 cell growth in dose-dependent fashion (Figure 1c), as we have reported previously (Hastings et al 2009). Wild type, PTHrP-negative H1944 cells underwent PTH1R knockdown to develop two independent knockdown clones along with two NTC clones.…”

“…In smooth muscle cells, the effects involve an increase in p27kip1, inhibition of cyclin dependent kinase activity and reduction of Rb phosphorylation, similar to the effects of PTHrP in H1944 lung cancer cells (Hastings et al 2009). …”

“…PTHrP and the cAMP analogs activated ERK in H1944 cells (Figure 3a; Figure 7b in Hastings et al 2009). ERK activation could either contribute to growth inhibition or limit it depending on the direction of the ERK effect.…”

Parathyroid Hormone-Related Protein (PTHrP): A Key Regulator of Life/Death Decisions by Tumor Cells with Potential Clinical Applications

“…When PTHrP production-lacking lung adenocarcinoma cells, transfected with with a pciNeo-PTHrP 1–87 expression plasmid, were examined for their growth and intracellular signalization aspects, the reduced mitogenesis observed was found linked to a block in G 1 and, from a molecular point of view, to the decreased expression of cyclin D2 and cyclin A2, increased expression of p27, decreased association of cyclin A2 and CDK2, and increased activation of ERK [30]. The authors, therefore, stressed the necessity of further investigation to explore this promising association between N-terminal PTHrP, slowing of tumor progression and increased patient survival.…”