RET Regulates Human Medullary Thyroid Cancer Cell Proliferation through CDK5 and STAT3 Activation.

Medullary thyroid cancer (MTC) is a neuroendocrine tumor that arises from the parafollicular C-cells, which produces the hormone calcitonin. RET is a transmembrane receptor protein-tyrosine kinase, which is highly expressed in MTC. Our previous studies reported that cyclin-dependent kinase 5 (CDK5) plays a crucial role in cancer progression, including MTC. However, the role of CDK5 in GDNF-induced RET signaling in medullary thyroid cancer proliferation remains unknown. Here, we investigated RET activation and its biochemically interaction with CDK5 in GDNF-induced medullary thyroid cancer proliferation. Our results demonstrated that GDNF stimulated RET phosphorylation and thus subsequently resulted in CDK5 activation by its phosphorylation. Activated CDK5 further caused STAT3 activation by its specific phosphorylation at Ser727. Moreover, we also found that GDNF treatment enhanced ERK1/2 and EGR1 activity, which is involved in p35 activation. Interestingly, we identified for the first time that CDK5 physically interacted with RET protein in MTC. Overall, our results provide a new mechanism for medullary thyroid cancer cell proliferation, suggesting that targeting CDK5 may be a promising therapeutic candidate for human medullary thyroid cancer in the near future.

Left ventricular extracellular matrix remodeling in dogs with right ventricular apical pacing.

INTRODUCTION: Right ventricle (RV) apical pacing is associated with increased incidence of heart failure due to left ventricle (LV) desynchronization. We aim to investigate extracellular matrix (ECM) remodeling of the LV in dogs with atria-sensed RV apical pacing. METHODS AND RESULTS: Dogs with pacemakers underwent AV nodal ablation. After 12 weeks of atria-sensed obligatory RV pacing, LVs were separated into septum and lateral wall for analysis. Zymographic activity, including matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitors of metalloproteinase-1 (TIMP-1), TIMP-3, collagen transcript expression, and histology were examined in opposite portions of the LV to identify possible ECM remodeling changes by RV apical pacing. Compared with sham-operated dogs, increased interstitial fibrosis and fragmentation of myofibrils was found in the LV lateral wall in the pacing group. Collagen type II mRNA showed a significant 2-fold increase in the LV lateral wall in the pacing group. Although collagen type I mRNA was increased, the difference was not significant. Zymography demonstrated MMP-9 activity was enhanced in both the LV lateral wall and septum in the pacing group, but MMP-2 activity was enhanced in the LV lateral wall. Immunofluorescence stain confirmed the activation of MMP-2 and MMP-9 in the LV lateral wall in the pacing group. Protein expression of TIMP-1 and TIMP-3 showed regional differences in the pacing group and both proteins were increased in the LV lateral wall. CONCLUSION: LV dyssynchrony by RV apical pacing elicits heterogeneous ECM remodeling in the LV. These findings assist in the elucidation of the pathophysiology of LV desynchronization.

A comparison of elementary schoolchildren's exposure to arsenic and lead.

One hundred fifty seven fifth-grade students (aged 10-12 years) from three elementary schools in three different towns in Taichung County, Taiwan were chosen as study subjects for the present arsenic and lead exposure study. The three towns--Longgang, Shalach, and Shuntain--are known to be highly, moderately, and lightly (control) polluted by As and Pb, respectively. Spot morning urine samples of students were collected and analyzed for arsenic and lead. The levels of As in the urine of Longgang schoolchildren showed the highest value among the three schools, while those of the control group (Shuntain) had the lowest values. In addition, the levels of Pb in the urine of the schoolchildren in Shuntain were significantly lower than those in Longgang and Shalach, while the levels of Pb in the urine of the schoolchildren in Longgang and Shalach showed no significant difference. Results of daily intake of metals from the different exposure pathways (i.e., ingestion from drinking water, household dust and food, and inhalation from airborne particles) showed that the Longgang area had the highest daily intake of As and Pb among the three areas, while the lowest daily intake of As and Pb occurred in the control area (Shuntain). A significant correlation between the doses of daily intake and urinary concentrations of As (p = 0.002) and Pb (p = 0.020) was observed. This correlation suggests that the increase of unit dose of the daily intake for As resulted in an increase of 0.953 microg g(-1) creatinine of As, whereas the increase of unit dose of the daily intake for Pb led to an increase of 0.053 microg g(-1) creatinine of Pb. These data indicate that the level of As in urine increased about 18 times higher than that of Pb for the same amount of increase in daily intake.

Cdk5 regulates STAT3 activation and cell proliferation in medullary thyroid carcinoma cells.

The biological behaviors of thyroid cancer are varied, and the pathological mechanisms remain unclear. Some reports indicated an apparent aggregation of amyloid accompanying medullary thyroid carcinoma (MTC). Amyloid aggregation in neurodegeneration leads to hyperactivation of Cdk5 and subsequent neuronal death. Based on the connection with amyloid, the role of Cdk5 in MTC is worthy of investigation. Initially, the expression of Cdk5 and its activator, p35, in MTC cell lines was identified. Cdk5 inhibition by specific inhibitors or short interfering RNA decreased the proliferation of MTC cell lines, which reveals the importance of Cdk5 in MTC cell growth. Although p35 cleavage has been considered as an important element in neurodegeneration, it seems that p35 cleavage was not a major cause in Cdk5 activity-dependent MTC cell proliferation because neither Cdk5 activity nor cell growth was affected by the inhibition of p35 cleavage. Clearance of amyloid by antibody neutralization indicated that MTC cell proliferation was supported by calcitonin-derived extracellular amyloid and subsequent Her2 and Cdk5 activation. Significantly, the STAT3 pathway was involved in Cdk5-dependent proliferation of MTC cells through Ser-727 phosphorylation. In addition, Cdk5 inhibition reduced nuclear distributions of both the Cdk5-p35 complex and phospho-STAT3 in MTC cells. Finally, Cdk5 inhibition retarded tumor formation in vivo accompanying the reduction of phospho-STAT3. Our findings suggest the first demonstration of a novel and specific role for Cdk5 kinase in supporting the proliferation of the medullary thyroid carcinoma cells and could shed light on a new field for diagnosis and therapy of thyroid cancer.