Heterotopic ossification within an arthroscopic portal after uneventful partial meniscectomy.

We report the case of a 44-year-old man who underwent a partial medial meniscectomy for a meniscal tear whose postoperative course was complicated by the development of heterotopic ossification (HO) within the medial arthroscopic portal. Following a routine initial procedure, the patient presented with ongoing pain and a palpable, painful lump around the previous medial arthroscopy portal. Plain radiographs and MRI were suggestive of a bony structure within the soft tissues.

Downregulation of COP9 signalosome subunits differentially affects the CSN complex and target protein stability.

Background: The COP9 signalosome (CSN) is a conserved protein complex in eukaryotic cells consisting of eight subunits (CSN1 to CSN8). Recent data demonstrate that the CSN is a regulator of the ubiquitin (Ub) proteasome system (UPS). It controls substrate ubiquitination by cullin-RING Ub ligases (CRLs), a process that determines substrate specificity of the UPS.

Ubiquitin system: JAMMing in the name of the lid.

The isopeptide bonds formed by ubiquitin or its relatives are cleaved by hydrolases with active site cysteines. Recent studies have revealed that similar metalloprotease motifs--JAMMs--in the Rpn11 subunit of the 26S proteasome lid and in the Csn5 subunit of the COP9 signalosome are involved in deubiquitination and deneddylation, respectively.