Veronika Siegl

The Role of Cdk5 in Neuroendocrine Thyroid Cancer

Medullary thyroid carcinoma (MTC) is a neuroendocrine cancer that originates from calcitonin-secreting parafollicular cells, or C cells. We found that Cdk5 and its cofactors p35 and p25 are highly expressed in human MTC and that Cdk5 activity promotes MTC proliferation. A conditional MTC mouse model was generated and corroborated the role of aberrant Cdk5 activation in MTC. C cell-specific overexpression of p25 caused rapid C cell hyperplasia leading to lethal MTC, which was arrested by repressing p25 overexpression. A comparative phosphoproteomic screen between proliferating and arrested MTC identified the retinoblastoma protein (Rb) as a crucial Cdk5 downstream target. Prevention of Rb phosphorylation at Ser807/Ser811 attenuated MTC proliferation. These findings implicate Cdk5 signaling via Rb as critical to MTC tumorigenesis and progression.

Ursolic acid from Trailliaedoxa gracilis induces apoptosis in medullary thyroid carcinoma cells.

Medullary thyroid carcinoma (MTC) originates from the C-cells of the thyroid and is not sensitive to radiation or chemotherapy. Therefore, surgical removal of the tumor tissue in its entirety is the only curative treatment for MTC. The present study aimed to examine the potential mechanisms of action of extracts of Trailliaedoxa gracilis (TG; WW Smith & Forrest), a plant from the province of Sichuan, China, and of ursolic acid (UA), a pentacyclic triterpen present in TG, on the MTC-SK MTC cell line. A total of 13 TG fractions and UA were examined in vitro for their effects on cell morphology, cell number, proliferation and rates of apoptosis. Reverse transcription-quantitative polymerase chain reaction of nuclear factor-κB essential modifier (NEMO) was performed to delineate the role of the apoptotic pathway following treatment with UA. TG and UA were examined in vivo in xenotransplanted MTC-bearing severe combined immunodeficient mice. The TG fractions exhibited antiproliferative effects, with inhibition of mitochondrial activity in the tumor cells at concentrations, which caused no impairment of the normal control cells. The apoptotic rates of the MTC-SK cells treated with the TG fractions and UA were determined, in which no marked tumor inhibition was observed in the treated MTC-mice, and no change in the expression of NEMO was detected in the treated MTC-SK cells. The observation of early-onset activation of caspase 8 suggested that the responsible factor was linked to NEMO, an anti-apoptotic protein. However, no differences in the mRNA transcription levels of NEMO were detected in MTC-SK cells treated with UA, suggesting that this protein was not associated with the signal transducer and activator of transcription 3 pathway.

Effect of Interferon-γ and LPS on Tetrahydrobiopterin in Rat PC 12 and Human KNA Cells

Abstract The first human phaeochromocytorna cell line KNA was tested with regard to stimulation of dopamine biosynthesis by nicotinamide adenine dinucleotide (NADH). Differently from rat phaeochromocytoma cells - clone PC12, where NADH increased dopamine biosynthesis significantly, no stimulation in KNA cells was found. NADH is effective on speeding up the formation of the active cofactor tetrahydrobiopterin by a recycling pathway via the dihydropteridinreductase system. Another way of formation of tetrahydrobiopterin is the induction of de novo synthesis by cytokines such as interferon-y or by lipopolysaccharide via activation of GTP cyclohydrolase I, as shown in rnacrophages. Neither rat PC12 nor human KNA cells showed in vitro a stimulation of tetrahydrobiopterin de novo synthesis by interferon-y and/or lipopolysaccharide.