Validation of potential therapeutic targets in alveolar soft part sarcoma: an immunohistochemical study utilizing tissue microarray.

AIMS: The molecular signature of alveolar soft part sarcoma (ASPS) is a specific der(17)t(X;17)(p11.2;q25) translocation, resulting in a chimeric transcription factor (ASPSCR1-TFE3). When this disease is no longer amenable to surgical curative intervention, uniformly efficacious therapies are lacking. The aim of this study was to evaluate the expression of potential molecular therapeutic targets in a cohort of ASPS tumour samples. METHODS AND RESULTS: Immunohistochemical analysis for hepatocyte growth factor, c-Met, phosphorylated c-Met, phosphorylated AKT, phosphorylated MEK, epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), p53 and vimentin was performed on an ASPS tissue microarray, yielding complete data from 26 tumours. Activation of c-Met and its downstream effectors was noted, whereas only limited EGFR expression was seen. VEGF was expressed to varying degrees. Only one sample exhibited strong nuclear p53 expression, while 10 expressed low levels. Vimentin expression was negative in the vast majority of samples (96%). CONCLUSIONS: There is a crucial need for better anti-ASPS therapies. Activated c-Met and the phosphorylation of its downstream effectors validate an intact signalling cascade probably induced by the ASPSCR1-TFE3 chimeric transcription factor. The angiogenic phenotype of these tumours is supported by increased angiogenic factor expression. Combination therapies targeting both tumour cells and angiogenesis merit further investigation.

The 19S proteasome ATPase Sug1 plays a critical role in regulating MHC class II transcription.

Emerging evidence in yeast suggests roles for ATPases of the 19S proteasome as mediators of transcriptional systems through their association with actively transcribed promoters, facilitation of clearance of paused elongation complexes and recruitment of coactivators. Although 19S subunits also regulate mammalian transcription, their role in recruiting transcription factors remains unclear. Here, we demonstrate for the first time a role for the 19S proteasome ATPase Sug1 in regulating transcription of the critical adaptive immune gene, MHC class II. Sug1 associates with the class II transactivator, CIITA, and with the MHC class II proximal promoter. In the absence of Sug1, HLA-DR promoter activity and MHC class II transcription are decreased. Critically, CIITA association with the MHC II promoter is dramatically decreased when Sug1 expression is reduced, even under conditions of proteasome inhibition. In contrast to the rapid promoter association of the 19S subunit, a 20S proteasome subunit associates with the MHC class II proximal promoter following prolonged cytokine stimulation and its association corresponds with pronounced promoter disassociation of CIITA. Taken together, these data demonstrate that both 19S and 20S subunits of the 26S proteasome play specific and critical roles in regulating CIITA activity and MHC class II transcription.