The Ubiquitin-Proteasome Reporter GFPu Does Not Accumulate in Neurons of the R6/2 Transgenic Mouse Model of Huntington's Disease

Impairment of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the selective dysfunction and death of neurons in polyglutamine disorders such as Huntington's disease (HD). The fact that inclusion bodies in HD mouse models and patient brains are rich in ubiquitin and proteasome components suggests that the UPS may be hindered directly or indirectly by inclusion bodies or their misfolded monomeric or oligomeric precursors. However, studies into UPS function in various polyglutamine disease models have yielded conflicting results, suggesting mutant polyglutamine tracts may exert different effects on the UPS depending on protein context, expression level, subcellular localisation and cell-type. To investigate UPS function in a well-characterised mouse model of HD, we have crossed R6/2 HD mice with transgenic UPS reporter mice expressing the GFPu construct. The GFPu construct comprises GFP fused to a constitutive degradation signal (CL-1) that promotes its rapid degradation under conditions of a healthy UPS. Using a combination of immunoblot analysis, fluorescence and immunofluorescence microscopy studies, we found that steady-state GFPu levels were not detectably different between R6/2 and non-R6/2 brain. We observed no correlation between inclusion body formation and GFPu accumulation, suggesting no direct relationship between protein aggregation and global UPS inhibition in R6/2 mice. These findings suggest that while certain branches of the UPS can be impaired by mutant polyglutamine proteins, such proteins do not necessarily cause total blockade of UPS-dependent degradation. It is therefore likely that the relationship between mutant polyglutamine proteins and the UPS is more complex than originally anticipated

Prognostic significance of calcitonin immunoreactivity, amyloid staining, and flow cytometric DNA measurements in medullary thyroid carcinoma

The proven power of DNA ploidy to predict mortality risk in medullary thyroid carcinoma (MTC) may be weakened when analyzed in conjunction with calcitonin immunoreactivity (CI) and amyloid staining (AS) of tumors. In this study 12 prognostic variables, including DNA ploidy, CI, and AS, were studied in 65 patients with MTC (57 sporadic; mean age 51 years) treated during 1946 through 1970. Cause-specific mortality rates at 10 and 15 years were 15% and 26%, respectively. By univariate analysis, TNM stages III or IV (p < 0.0001), tumor unresectability (p < 0.0001), male sex (p = 0.019), negative AS (p = 0.032), and low CI (p = 0.033) were significant predictors of increased mortality rates. DNA ploidy (p = 0.058) and inheritance pattern (p = 0.25) were nonsignificant. By multivariate analysis, only TNM stage, tumor resectability, and AS were independently significant (p < 0.005). A prognostic model was created, based on presence or absence of these independent risk factors, and four risk groups were defined, capable of predictably defining mortality rates in MTC (p < 0.0001). The model requires validation in larger series and independent verification by others. However, we believe that a risk-group scheme for MTC based on AS, disease stage, and completeness of tumor resection may have wide applicability and prove relevant to clinicians treating this disease