Ras signaling through PI3K confers hormone-independent proliferation that is compatible with differentiation

Dedifferentiation of thyroid carcinoma is accompanied by increased accumulation of the PET tracer 18 F-FDG. The molecular mechanisms responsible for this phenomenon are poorly understood. Therefore, we studied the regulation of 18 F-FDG uptake by the human follicular thyroid carcinoma cell line ML-1 and the as-yetunknown oncogene expression of that cell line. The data obtained in ML-1 were compared with those of a well-differentiated thyroid cell line of rat origin . Methods: The expression of the thyroid-stimulating hormone (TSH) receptor was investigated by immunocytochemistry, and the expression of the glucose transporters (GLUTs) was determined by Western blotting. Mutation analysis of ML-1 was performed for K-ras codons 12 and 13. The effect of TSH on intracellular cAMP levels was determined by a competitive enzyme immunoassay. Cells were incubated with 18 F-FDG (0.5-1.0 MBq/mL) for 1 h, and tracer uptake was related to protein concentration. The effects of bovine TSH, the cAMP analog (Bu) 2 cAMP, and the phosphatidylinositol-3-kinase (PI3-kinase) inhibitor LY294002 on 18 F-FDG uptake were investigated. Results: The TSH receptor was present in both cell lines. FRTL-5 clearly expressed GLUT-1 and also GLUT-4. In ML-1 only, the expression of GLUT-3 was detected. TSH and (Bu) 2 cAMP had a significant effect on 18 F-FDG uptake or GLUT-1 expression in FRTL-5, but not in ML-1 cells. PI3-kinase inhibition by LY294002 downregulated 18 F-FDG uptake in FRTL-5 by 58% 6 9% (n 5 6) and in ML-1 by 26% 6 5% (n 5 42, both P , 0.05). Mutation analysis of ML-1 cells revealed a Gly12Ser point mutation at codon 12 of the K-ras gene. Conclusion: 18 F-FDG uptake in the thyroid carcinoma cell line ML-1 is no longer regulated by TSH or cAMP or mediated by GLUT-1. However, in this cell line, this variable is still governed to some extent by PI3-kinase located downstream to the constitutively active K-ras in the Ras-PI3-kinase-Akt pathway. These data suggest that increases in 18 F-FDG uptake in thyroid carcinomas observed in vivo by PET may reflect activation of intracellular signal transduction cascades by oncogenes.

show abstract

“…This cross-talk seems organ-specific and has been demonstrated for glucose uptake (7,8) and cell proliferation (26,27).…”

Section: Discussionmentioning

confidence: 99%

Regulation of Uptake of¹⁸F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Prante¹,

Maschauer²,

Frémont³

et al. 2009

J Nucl Med

View full text Add to dashboard Cite

show abstract

“…bFGF, HGF as well as EGF are all able to induce robust DNA synthesis in synergy with TSH or insulin. In FRTL-5 cells proliferation induced by TSH or by cAMP requires RAS, AKT and PI3K signalling (Cass & Meinkoth, 2000;Ciullo et al, 2001). RAS activity is apparently necessary for TSH to induce the transition from quiescence to G1, though the ERK pathway seems not involved.…”

Section: Biochemical Aspects Of Signal Transduction and Cell Cycle Rementioning

confidence: 99%

Molecular Biology of Thyroid Cancer

Viglietto¹,

Marco²

2011

Contemporary Aspects of Endocrinology

View full text Add to dashboard Cite

“…RasL61 adenovirus was infected at a multiplicity of infection (MOI) of 5 infectious units/cell (IU/cell, as determined by titration in 293 cells) and RasV12 at MOI of 3.5 IU/cell, conditions where >95% of the cells were infected. RasV12-transformed WRT cells (15,16) were propagated in the same medium as WRT cells, with the addition of geneticin (150 Ag/mL).…”

Section: Introductionmentioning

confidence: 99%

Ras Induces Chromosome Instability and Abrogation of the DNA Damage Response

Abulaiti

Fikaris²,

Tsygankova³

et al. 2006

Cancer Research

View full text Add to dashboard Cite

Ras mutations are frequent in thyroid tumors, the most common endocrine malignancy. The ability of Ras to transform thyroid cells is thought to rely on its mitogenic activity. Unexpectedly, acute expression of activated Ras in normal rat thyroid cells induced a DNA damage response, followed by apoptosis. Notably, a subpopulation of cells evaded apoptosis and emerged with features of transformation, including the loss of epithelial morphology, dedifferentiation, and the acquisition of hormone-and anchorage-independent proliferation. Strikingly, the surviving cells showed marked chromosomal instability. Acutely, Ras stimulated replication stress as evidenced by the induction of ataxia telangiectasia mutated and Rad3-related protein kinase (ATR) activity (Chk1 phosphorylation) and of ;H2A.X, a marker of DNA damage. Despite the activation of a checkpoint, cells continued through mitosis in the face of DNA damage, resulting in an increase in cells harboring micronuclei, an indication of defects in chromosome segregation and other forms of chromosome damage. Cells that survived exposure to Ras continued to exhibit replication stress (ATR activation) but no longer exhibited ;H2A.X or full activation of p53. When rechallenged with Ras or DNA-damaging agents, the surviving cells were more resistant to apoptosis than parental cells. These data show that acute expression of activated Ras is sufficient to induce chromosomal instability in the absence of other signals, and suggest that Ras-induced chromosomal instability arises as a consequence of defects in the processing of DNA damage. Hence, abrogation of the DNA damage response may constitute a novel mechanism for Ras transformation. (Cancer Res 2006; 66(21): 10505-12)

show abstract

Ras signaling through PI3K confers hormone-independent proliferation that is compatible with differentiation

Cited by 52 publications

References 61 publications

Regulation of Uptake of¹⁸F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Regulation of Uptake of¹⁸F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Molecular Biology of Thyroid Cancer

Ras Induces Chromosome Instability and Abrogation of the DNA Damage Response

Contact Info

Product

Resources

About

Ras signaling through PI3K confers hormone-independent proliferation that is compatible with differentiation

Cited by 52 publications

References 61 publications

Regulation of Uptake of18F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Regulation of Uptake of18F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Molecular Biology of Thyroid Cancer

Ras Induces Chromosome Instability and Abrogation of the DNA Damage Response

Contact Info

Product

Resources

About

Regulation of Uptake of¹⁸F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras

Regulation of Uptake of¹⁸F-FDG by a Follicular Human Thyroid Cancer Cell Line with Mutation-Activated K-Ras