Title

Sequestosome1 (SQSTM1) and the molecular genetics of Paget's Disease of Bone

Date of Completion

January 2008

Keywords

Biology, Molecular|Biology, Genetics|Biology, Cell

Degree

Ph.D.

Abstract

Background. Paget's Disease of Bone (PDB) is an exaggerated bone remodeling disease that results in abnormal skeletal structure, and in rare cases progresses to osteosarcoma. Genetic studies of familial PDB have revealed that most germline mutations lie within the Sequestosome1 gene (SQSTM1). Interestingly, all known mutations associated with familial PDB cluster around the conserved domain of the encoded p62SQSTM1 protein, which is a critical scaffold for signaling pathways. In contrast to familial PDB, little is known about the role of mutations in SQSTM1 in the etiology of sporadic PDB. To better elucidate the molecular pathogenesis of sporadic Paget's disease, we hypothesized that somatic SQSTM1 mutations may occur within the pagetic tissues.^ Materials and methods. Laser microdissection was used to capture populations of pagetic cells from bone sections of patients with sporadic PDB, as well as matched normal and tumor sets of patients with sporadic Paget's osteosarcoma. ^ DNA was extracted from these captured cells, from blood samples of patients with sporadic PDB, and appropriate controls, for sequence analysis and allelic discrimination.^ Results. SQSTM1C1215T mutations were found in affected bone from two patients with sporadic PDB but not in their blood samples, indicating the somatic origin of the mutations. Curiously, not all affected cells carried the mutation, suggesting that the pagetic bone was mosaic for the mutation. Three of five pagetic osteosarcoma samples had the SQSTM1C1215T mutation. None of the adolescent primary osteosarcoma samples showed any mutations.^ Conclusions. The discovery of somatic SQSTM1 mutations in sporadic PDB and pagetic osteosarcoma demonstrates a role for SQSTM1 in both sporadic and inherited PDB. The varying frequency of mutations in the pagetic cells suggests involvement of SQSTM1 in the progression of PDB. The occurrence of these somatic mutations is a paradigm shift in our understanding of this disease. Future studies will focus on which bone cells harbor these mutations or whether other stromal cells in the tumor microenvironment are also affected. This may help us better understand the dynamics associated with pathological skeletal remodeling. ^