Establishment of two human small cell lung cancer cell lines: the evidence of accelerated production of parathyroid hormone-related protein with tumor progression

Parathyroid hormone-related protein (PTHrP) and malignancy

PTHrP (parathyroid hormone related protein) is an important mediator of malignancy-related tumor progression and hypercalcemia that shares considerable homology and functionality with parathyroid hormone. In this chapter, we review what has been elucidated to date regarding PTHrP's role in malignancies. Starting with a review of calcium metabolism and regulation, we then summarize the discovery and structure of PTHrP and development of sensitive immunoassays for specific measurement. Subsequently, we explore its role in tumor progression, with emphasis on the primary tumor as well as skeletal and non-osseus metastases. We then consider the clinical implications of PTHrP in cancer before concluding with a discussion of both established and potential treatments for malignancy associated hypercalcemia and bone metastases.

Parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor type 1 expression in human lung adenocarcinoma

BACKGROUND

In many primary tumors, parathyroid hormone-related peptide (PTHrP) and PTHrP type 1 receptor (PTH1R) are coexpressed, supporting the possibility that PTHrP/PTH1R system can mediate important signals for tumor progression through paracrine/autocrine mechanisms. In non-small cell lung carcinoma the clinical relevance of the expression of PTH1R remains to be investigated.

METHODS

Fifty-four lung adenocarcinomas of mixed histologic type from patients with stage I and II cancer were assayed by quantitative immunohistochemistry for the expression of PTHrP and PTH1R.

RESULTS

PTHrP and PTH1R were expressed in a wide range of intensity in the cytoplasm of tumor cells, and their values showed a positive correlation. PTH1R, but not PTHrP, was expressed by plasma cells infiltrating the tumor stroma. PTHrP and PTH1R were not associated with age, tumor diameter, or histopathologic grading, whereas they were directly associated with lymph node involvement at presentation. Cox regression analysis, using PTHrP and PTH1R as continuous covariates, showed that the covariate levels were directly associated with the risk of death and metastasis. Patients whose tumors coexpressed high levels of PTHrP and PTH1R showed the highest risk of metastasis (relative risk, 5.89; 95% CI, 2.1-16.6; P = .0003) and death (relative risk, 6.24; 95% CI, 1.6-23.9; P = .0033). The presence of PTH1R-positive plasma cells in the tumor stroma was associated with a more favorable survival rate independently from the PTHrP status of the tumor.

CONCLUSION

The paracrine/autocrine signaling through PTHrP/PTH1R could be important in early-stage lung adenocarcinoma progression.

Parathyroid hormone-related protein and ezrin are up-regulated in human lung cancer bone metastases

Lung cancer often metastasizes to bone in patients with advanced disease. Identification of the factors involved in the interactions between lung cancer cells and bone will improve the prevention and treatment of bone metastases. We identified changes in metastasis-related gene expression of human HARA lung squamous carcinoma cells co-cultured with neonatal mouse calvariae using a pathway-specific microarray analysis. Nine genes were up-regulated and two genes down-regulated in HARA cells co-cultured with mouse calvariae. Five of the nine up-regulated genes, including caveolin 1, CD44, EphB2, ezrin, and Parathyroid hormone-related protein (PTHrP), and one down-regulated gene, SLPI, were further confirmed by Reverse transcription-polymerase chain reaction (RT-PCR). A mouse model was subsequently used to study the role of PTHrP and ezrin in bone metastasis in vivo. PTHrP (all three isoforms) and ezrin were up-regulated in HARA cells at sites of bone metastasis as detected by RT-PCR and immunohistochemistry. The PTHrP 141 mRNA isoform was increased by the greatest extent (13.9-fold) in bone metastases compared to PTHrP 139 and PTHrP 173 mRNA. We then generated a HARA cell line in which PTHrP expression was inducibly silenced by RNA interference. Silencing of PTHrP expression caused significant reduction of submembranous F-actin and decreased HARA cell invasion. Ezrin up-regulation was confirmed by Western blots on HARA cells co-cultured with adult mouse long bones. Further, Transforming growth factor beta (TGF-beta) was identified as one of the factors in the bone microenvironment that was responsible for the up-regulation of ezrin. The identification of PTHrP and ezrin as important regulators of lung cancer bone metastasis offers new mechanistic insights into the metastasis of lung cancer and provides potential targets for the prevention and treatment of lung cancer metastasis.

Skeletal metastasis: Established and emerging roles of parathyroid hormone related protein (PTHrP)

Parathyroid hormone related protein (PTHrP) is a well characterized tumor derived product that also has integral functions in normal development and homeostasis. PTHrP is produced by virtually all tumor types that metastasize to bone and numerous studies have demonstrated a correlation between PTHrP expression and skeletal localization of tumors. PTHrP has prominent effects in bone via its interaction with the PTH-1 receptor on osteoblastic cells. Through indirect means, PTHrP supports osteoclastogenesis by upregulating the receptor activator of NFkappaB ligand (RANKL) in osteoblasts. PTHrP also regulates osteoblast proliferation and differentiation in manners that are temporal and dose dependent. Bone turnover has been implicated in the localization of tumors to bone and PTHrP increases bone turnover. Bone turnover results in the release of growth factors such as TGFbeta and minerals such as calcium, both of which impact tumor cell growth and contribute to continued PTHrP production. PTHrP also has anabolic properties and could be in part responsible for osteoblastic type reactions in prostate cancer. Finally, emerging roles of PTH and PTHrP in the support of hematopoietic stem cell development in the bone marrow microenvironment suggest that an interaction between hematopoietic cells and tumor cells warrants further investigation.

Sex-Specific Survival Advantage with Parathyroid Hormone–Related Protein in Non–Small Cell Lung Carcinoma Patients

PURPOSE

Parathyroid hormone-related protein (PTHrP) is commonly expressed in non-small cell lung carcinomas (NSCLC). Expression of the protein could have implications for progression of the disease because it regulates cancer cell growth, apoptosis, and angiogenesis. However, its relationship with survival has not been evaluated in a large-scale investigation.

EXPERIMENTAL DESIGN

PTHrP expression was assessed in paraffin-embedded tumor samples from 407 patients with NSCLC by immunohistochemistry. A pathologist unaware of the clinical history classified specimens as PTHrP positive or PTHrP negative. The log-rank test was used to compare survivals of PTHrP-positive and PTHrP-negative groups, and Cox regression was used to adjust for additional covariates.

RESULTS

Median survival was 55 versus 22 months (P < 0.001) in female patients with and without tumor PTHrP, respectively. Male survival was 38 months independent of PTHrP status. Stage, histology, age, and smoking history were also associated with increased longevity. PTHrP remained a significant predictor of survival for female patients after controlling for stage, histology, and age.

CONCLUSIONS

In this study, PTHrP expression was associated with a survival advantage in female patients. Additional investigations must be done to ascertain whether the result is reproducible and independent of potential confounding covariates. Sex-dependent effects of PTHrP in lung cancer would open new avenues of research into the role of sex in cancer progression.

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.

Parathyroid hormone-related protein and lung biology

Parathyroid hormone-related protein (PTHrP) is expressed in normal and malignant lung and has roles in development, homeostasis, and pathophysiology of injury and cancer. Its effects in developing lung include regulation of branching morphogenesis and type II cell maturation. In adult lung, PTHrP stimulates disaturated phosphatidylcholine secretion, inhibits type II cell growth, and sensitizes them to apoptosis. In lung cancer, PTHrP may play a role in carcinoma progression, or metastasis. The protein could be a useful marker for assessing lung maturity or type II cell function, predicting risk of injury, and detecting lung cancer. PTHrP-based therapies could also prove useful in lung injury and lung cancer.

Parathyroid hormone-related protein ameliorates death receptor-mediated apoptosis in lung cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed in more advanced, aggressive tumors and may play an active role in cancer progression. This study investigated the effects of PTHrP on apoptosis after UV irradiation, Fas ligation, or staurosporine treatment in BEN human squamous lung carcinoma cells. Cells at 70% confluency were treated for 24 h with 100 nM PTHrP-(1-34), PTHrP-(38-64), PTHrP-(67-86), PTHrP-(107-139), or PTHrP-(140-173) in media with serum, exposed for 30 min to UV-B radiation (0.9 mJ/cm2), and maintained for another 24 h. Caspase-3, caspase-8, and caspase-9 activities increased fivefold. Pretreatment with PTHrP-(1-34) and PTHrP-(140-173) ameliorated apoptosis after UV irradiation, as indicated by reduced caspase activities, increased cell protein, decreased nuclear condensation, and increased clonal survival. Other peptides had no effect on measures of apoptosis. PTHrP-(140-173) also reduced caspase activities after Fas ligation by activating antibody, but neither peptide had effects on caspase-3 or caspase-9 activity after 1 microM staurosporine. These data indicate that PTHrP-(1-34) and PTHrP-(140-173) protect against death receptor-induced apoptosis in BEN lung cancer cells but are ineffective against mitochondrial pathways. PTHrP contributes to lung cancer cell survival in culture and could promote cancer progression in vivo. The mechanism for the protective effect against apoptosis remains to be determined.

Parathyroid hormone-related protein regulates the growth of orthotopic human lung tumors in athymic mice

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has growth regulatory effects for many malignant cells and may influence the progression of carcinomas of the breast, prostate, and lung. In the current study, the authors investigated the in vivo and in vitro effects of PTHrP neutralizing antibody and PTHrP treatment on the growth of BEN cells, a human lung squamous cell carcinoma line that expresses PTHrP and its receptor.

METHODS

Orthotopic lung tumors were produced in 20 athymic mice with BEN-GFP cells (a clonal line that stably expresses green fluorescent protein [GFP]) by instilling suspensions of 3 x 10(6) cells per mouse into the lungs of anesthetized animals. The mice were divided into 2 groups receiving either subcutaneous mouse antihuman PTHrP antibodies or irrelevant mouse immunoglobulin (Ig) G (150 microg) twice weekly.

RESULTS

After 30 days, 6 of 10 mice receiving anti-PTHrP antibodies had lung tumors visible on macroscopic inspection, but only 1 of the 10 mice treated with irrelevant IgG had a lung tumor that was of that size (P < 0.01). GFP fluorescence was significantly greater in lung homogenates of the PTHrP antibody-treated mice than in the mice treated with IgG (6006 +/- 411 vs. 2907 +/- 282 relative fluorescent units, respectively; P < 0.001). Although neutralizing antibodies stimulated BEN cell lung tumor growth, exogenous PTHrP 1-34 treatment (0.01-1 nM) inhibited the growth of cultured BEN cells by approximately 40%.

CONCLUSIONS

Although PTHrP expression has been reported to be associated with more aggressive malignancies, the data from the current study suggest that PTHrP 1-34 was a paracrine growth inhibitor in BEN human lung carcinoma cells. The growth-related effects of PTHrP are complex, and can be both stimulatory and inhibitory.