肿瘤细胞信号转导汇.ppt

* * * * * HH signaling is linked to an increasing number of cancers * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * LEF/TCF Wnt CK1 GSK-3b APC b-catenin axin Frizzled LRP E-cadherin Wnt signaling pathway C. Liu et al. 2002. Cell 108:837. Complicated phosphorylation controls b-catenin stability How does b-catenin reach target genes? ? LEF/TCF transcription factors ? HMG (High Mobility Group) proteins ? mammalian LEF-1 and TCF-1 identified in T lymphocytes in 1991 ? two more members cloned by low stringency screening of Libraries and degenerate PCR in 1993 ? b-catenin was used in a yeast two-hybrid assay and LEF-1 was cloned as an interacting protein in 1997 - endpoint of the pathway determined - merged two independent groups of scientists - subcellular localization of b-catenin finally settled General Structure of LEF/TCF Transcription Factors b-catenin binding Co-repressor binding DNA binding/ bending alt. COOH TCF-1 TCF-3 TCF-4 NLS HMG N LEF-1 B B B E E E 94% 96% 99% 55% 52% 64% Target Genes of Wnt Signaling ? cell cycle regulators and transcription factors -c-MYC -cyclin D1 ? tissue specific genes ? tissue remodeling proteins - matrix metalloproteinases - ephrin receptors and ligands - adhesion proteins ? angiogenesis - VEGF In the absence of Wnt signaling: NLS HMG N LEF-1 B NLS HMG N dnLEF-1 B Groucho LEF/TCF Wnt GSK-3b axin Frizzled LRP APC LEF/TCF LEF/TCF LEF/TCF LEF/TCF LEF/TCF LEF/TCF LEF/TCF LEF/TCF Activation of LEF-1 target genes can transform cells Aoki, M. et al. 1999. Proc. Natl. Acad. Sci. USA. 96:139-144 anchorage-independent growth contact inhibition colony formation Adenomatous Polyposis Coli ? Identified by Joanna Groden and Ray White as a tumor suppressor gene suffering LOH in families with very high rates of colon cancer. ? Truncation mutations or loss of the entire gene occurs in most Sporadic colon cancers ? /~rnusse/wntwindow.htm Hereditary colorectal cancer (~ 15%) Familial Adenomat