The role of SPARC in the TRAMP model of prostate carcinogenesis and progression

SPARC (Secreted Protein Acidic and Rich in Cysteine), is a matricellular glycoprotein that is produced by tumor and/or neighboring stroma. In human prostate cancer, SPARC immunoreactivity is highest in metastatic lesions but distinct contributions of tumoral and stromal SPARC to tumorigenesis and progression are unclear. To determine the role of SPARC in primary prostate tumorigenesis, we crossed SPARC-null (SP(-/-)) with TRAMP (Transgenic Adenocarcinoma of Mouse Prostate) mice. TRAMP(+)/SP(-/-) mice exhibited accelerated cancer development and progression. Compared to their TRAMP(+)/SP(-/-) counterparts, TRAMP(+)/SP(+/+) tumors had fewer proliferating cells, and decreased cyclins A and D1 with increased p21(Cip) and p27(Kip). Similar effects on proliferation and cell-cycle regulators were observed in human prostate cancer cell lines, transiently transfected with pSPARC. TRAMP(+)/SP(-/-) tumors exhibited decreased stromal collagen, enhanced matrix metalloproteinase activity and increased vascular endothelial growth factor, proinflammatory cytokines. To determine the contribution of stromal SPARC, we evaluated subcutaneous tumor growth of TRAMP cell lines in syngeneic SP(+/+) and SP(-/-) mice. Enhanced growth, decreased stromal collagen and increased proteolysis were noted in SP(-/-) mice. Our findings demonstrate that both tumor and stromal SPARC are limiting for primary prostate tumorigenesis and progression, through effects on the cell cycle and the creation of a less favorable tumor microenvironment.

The envelope gene is a cytopathic determinant of CCR5 tropic HIV-1

Late stage AIDS associated CCR5 tropic HIV-1 clones (R5-AIDS HIV-1) exhibit greater cytopathic effects (CPE) than earlier isolates from the same patients. In this study, envelopes from a series of three biological clones derived from the same patient were evaluated as a cytopathic determinant of R5-AIDS HIV-1 for thymocytes. In a single round of replication in thymocytes, the AIDS associated clone mediated greater initiation of reverse transcription. This enhancement was not due to broadened coreceptor tropism, as all clones studied were exclusively R5 tropic. The full-length R5-AIDS env mediated greater infectivity than R5 pre-AIDS env when used to pseudotype a reporter virus. R5-AIDS env pseudotypes were more resistant to TAK-779 and showed more rapid infection kinetics but similar resistance to a CD4 blocking mAb. We conclude that the enhanced thymic replication and CPE shown by the R5-AIDS clone is due to enhanced efficiency of Env-mediated entry via CCR5.