MOLECULAR AND FUNCTIONAL CHARACTERIZATION OF RECOMBINANT FRAGMENTS OF SPARC, A TUMOR PROGNOSIS-RELATED PROTEIN

CYNTHIA LÓPEZ HABER; FEDERICO PRADA; LEONARDO ALONSO; GONZALO DE PRAT GAY; OSVALDO PODHAJCER; ANDREA S. LLERA

Bariloche, Argentina

Congreso; XXXIX Reunión Anual de la Sociedad Argentina de Investigaciones Bioquímicas; 2003

SPARC is a matricellular glycoprotein that elicits changes in cell shape and proliferation. It was found to be overexpressed in different tumors, in association with tumor progression and metastasis. SPARC consists of three domains, named NT (for N-terminal), FS (for follistatin-like) and EC (for extracellular calcium-binding domain), each of which has showed unique structural and functional properties. Importantly, its NT domain consists in a highly acidic stretch of 52 amino acids, which is believed to be natively unfolded, that is, naturally lacking a defined secondary structure. In order to investigate the possibility that a disordered structure could account for some of many different SPARC activities, we decided to express recombinant human SPARC as well as fragments comprising the following domains: 1) FS-EC ,2 ) EC, 3) NT-FS . They were successfully expressed as soluble His-tag fusions in S3 D.melanogaster cell conditioned medium. CD spectra of the whole protein and the EC construction showed concordance with published structural characteristics, while the NT-FS fragment, although not disordered, lacks several secondary structure features. Initial studies on the effects of the fragments in cell proliferation show that, contrary to what is seen with the whole protein and other constructions, NT-FS enhances proliferation of HeLa and A375N tumor cell lines. Further studies are planned to confirm these observations as well as to evaluate the behavior of fragments on other aspects of tumor malignancy.