Telomerase-mediated lifespan extension of human bronchial cells does not affect hexavalent chromium-induced cytotoxicity or genotoxicity

Abstract

Hexavalent chromium (Cr(VI)) is a metal of increasing public health concern, as exposure to it is widespread and it is a well-established cause of human bronchial carcinomas and fibrosarcomas. The water-insoluble Cr(VI) salts are potent carcinogens compared to the water soluble salts; yet the genotoxic mechanisms of both may be mediated by soluble Cr(VI) ions. Currently, these mechanisms are poorly understood. Emerging evidence suggests that initial cell culture models used to study the general toxicity of Cr(VI) may be suboptimal for investigating mechanisms specific to human bronchial cells. Accordingly, we have developed a new model system of human bronchial cells by introducing hTERT, the catalytic subunit of human telomerase, into primary human bronchial fibroblasts (PHBF). We have isolated a stable, clonally derived cell line, WHTBF-6, that demonstrate reconstitution of telomerase activity and maintenance of telomere lengths with increasing culture age. WHTBF-6 has been characterized as having an extended in vitro lifespan, a normal growth rate, a normal diploid karyotype that is maintained over time, and exhibits serum-dependent contact-inhibited anchorage-dependent growth. Moreover, we find that both particulate and soluble hexavalent chromium induce a pattern and degree of cytotoxicity and clastogenicity in WHTBF-6 that is similar to the parental PHBF cells. Because telomerase does not compromise growth or the response to Cr(VI), our results indicate that this is an excellent system for studying the mechanisms of Cr(VI) and potentially other carcinogens implicated in the development of lung cancer.

Particulate Depleted Uranium Is Cytotoxic and Clastogenic to Human Lung Cells

“…However, in our study, soluble DU was not clastogenic. This difference may be due to the cell models studied; the cells in our study reflect the behavior of normal primary cells (20), and the HOS cells are derived from a tumor and may have alterations in genes critical for genomic stability. This possibility is supported by the fact that they only reported dicentrics chromosomes after DU exposure and not more common lesions such as chromatid and isochromatid lesions.…”

“…WTHBF-6 cells, a clonal cell line derived from normal human bronchial fibroblasts that ectopically express human telomerase, were used in all experiments. These cells have a similar doubling time (24 h) and clastogenic and cytotoxic responses to metals compared to those of their parent cells (20). Ectopically expressing telomerase can induce a variety of phenotypes in mass cultured cells from normal to genomically unstable cells (21); thus, this cell line was subcloned from a mass culture and chosen as a model system because it reflects the normal phenotype (20).…”

“…These cells have a similar doubling time (24 h) and clastogenic and cytotoxic responses to metals compared to those of their parent cells (20). Ectopically expressing telomerase can induce a variety of phenotypes in mass cultured cells from normal to genomically unstable cells (21); thus, this cell line was subcloned from a mass culture and chosen as a model system because it reflects the normal phenotype (20). After more than 1000 population doublings, these cells retain a normal diploid karyotype (data not shown).…”

Homologous recombination repair protects against particulate chromate-induced chromosome instability in Chinese hamster cells

“…Cr(VI) is a well-established human lung carcinogen and previous studies show that Cr(VI) chromium is most potent in particulate form. Particulate Cr(VI) induces DNA strand breaks, Cr-DNA adducts, Cr-DNA crosslinks and mutation to 6-thioguanine resistance in diploid human fibroblasts [8,[14][15][16][17]12,35,36], however how these lesions are repaired and their relationship to Cr(VI)-induced CIN are uncertain.…”

Chronic Exposure to Lead Chromate Causes Centrosome Abnormalities and Aneuploidy in Human Lung Cells

“…Studies using lead chromate as a model particulate Cr(VI) compound show that the particles partially dissolve outside the cell releasing Pb cations and chromate anions (7)(8)(9). The internalized Cr ions induce chromosome aberrations, DNA adducts, and DNA double-strand breaks (10)(11)(12)(13)(14)(15), whereas the internalized Pb ions are generally nongenotoxic (8,16). Two studies investigating potential epigenetic effects of Pb in lead chromate-induced carcinogenesis also show that Pb does not interfere with Crinduced cell death (17) or cause mitotic stimulation of Cr-damaged cells (18).…”