calpastatin and Sarcoma--Ewing

p107 protein, a member of the retinoblastoma family protein, suppresses growth promotion in cancer cells. We have already reported evidence that calpain, a calcium dependent protease is involved in the cleavage of p107 protein. We show here that p107 protein can also be a substrate for ubiquitination. A negative growth regulator, the HMG-CoA reductase inhibitor lovastatin was found to induce loss of p107 protein which was reversible by a specific protease inhibitor lactacystin as well as calpain inhibitor. Following treatment with lovastatin higher molecular weight ubiquitinated forms of p107 were detected by anti-p107 immunoprecipitation and anti-ubiquitin Western blotting. These forms further increased when lactacystin was added to culture medium. These results indicate that ubiquitin-proteasome pathway plays a potential role in the degradation as well as calpain. The data presented here suggest a model in which calpain and ubiquitin-proteasome system possibly play a cooperative role in targeting the protein under certain conditions.

Topics: Acetylcysteine; Antineoplastic Agents; Blotting, Western; Calcium-Binding Proteins; Calpain; CDC2-CDC28 Kinases; Cell Cycle; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinases; Cysteine Proteinase Inhibitors; Humans; Lovastatin; Male; Nuclear Proteins; Proliferating Cell Nuclear Antigen; Prostatic Neoplasms; Protein Serine-Threonine Kinases; Retinoblastoma Protein; Retinoblastoma-Like Protein p107; Sarcoma, Ewing; Transfection; Tumor Cells, Cultured; Ubiquitins