Recognition and elimination of malignant cells by cytotoxic T lymphocytes depends on antigenic peptides generated by proteasomes. It has been established that impairment of the immunoproteasome subunits, that is, PSMB8, PSMB9 and PSMB10 (PSMBs), is critical for malignant cells to escape immune recognition. We report here the regulatory mechanism of the repression of PU.1-dependent activation of PSMBs by PML/RARα in the pathogenesis of acute promyelocytic leukemia (APL) and the unidentified function of all-trans retinoic acid (ATRA) as an immunomodulator in the treatment of APL. Chromatin immunoprecipitation and luciferase reporter assays showed that PU.1 directly bound to and coordinately transactivated the promoters of PSMBs, indicating that PSMBs were transcriptional targets of PU.1 and PU.1 regulated their basal expression. Analysis of expression profiling data from a large population of acute myeloid leukemia (AML) patients revealed that the expression levels of PSMBs were significantly lower in APL patients than in non-APL AML patients. Further evidence demonstrated that the decrease in their expression was achieved through PML/RARα-mediated repression of both PU.1-dependent transactivation and PU.1 expression. Moreover, ATRA but not arsenic trioxide induced the expression of PSMBs in APL cells, indicating that ATRA treatment might activate the antigen-processing/presentation machinery. Finally, the above observations were confirmed in primary APL samples. Collectively, our data demonstrate that PML/RARα suppresses PU.1-dependent activation of the immunosubunits, which may facilitate the escape of APL cells from immune surveillance in leukemia development, and ATRA treatment is able to reactivate their expression, which would promote more efficient T-cell-mediated recognition in the treatment.

Objectives: The aim of this retrospective study was to characterize MRI findings of synovial chondromatosis in the temporomandibular joint (TMJ) by correlation with their pathological findings. Methods: 22 patients with synovial chondromatosis in unilateral TMJ were referred for plain MRI prior to surgical management and pathological examinations. Parasagittal and coronal proton density-weighted imaging and T 2 weighted imaging were performed for each case. Results: MRI demonstrated multiple chondroid nodules and joint effusion in all patients (100%) and amorphous iso-intensity signal tissues within expanded joint space and capsule in 19 patients (86.4%). On T 2 weighted imaging, signs of low signal nodules within amorphous iso-intensity signal tissues were used to determine the presence of attached cartilaginous nodules in pathology, resulting in 100% sensitivity, 60% specificity and 90.9% accuracy. Signs of low and intermediate signal nodules within joint fluids were used to detect loose cartilaginous nodules and resulted in 80% sensitivity, 42.9% specificity and 68.2% accuracy. Conclusions: MRI of synovial chondromatosis in TMJ was characterized by multiple chondroid nodules, joint effusion and amorphous iso-intensity signal tissues within the expanded space and capsule. The attached cartilaginous nodules in pathology were better recognized than the loose ones on MRI. Plain MRI was useful for clinical diagnosis of the disorder.

We report the case of a woman who had secondary chondrosarcoma in an osteochondroma in the left mandibular condyle, presenting as a large lobulated bone density mass in the left condyle process, to illustrate the clinical characteristics and imaging findings.