Thrombospondin-1 Is Modulated by the B-RafV600E Pathway in Papillary Thyroid Cancer
C Nucera, A Porrello, Z Antonello, S Finn, C Priolo, T Giordano, B Jarzab, F Trimarchi, A Pontecorvi, V Nose, J Lawler, S Parangi. MGH, Harvard Medical School (HMS), Boston; Beth Israel Deaconess Medical Center, HMS, Boston; Duke Univ, Durham; DFCI, HMS, Boston; Michigan Univ, MI; Gliwice Univ, Gliwice, Poland; Messina Univ, Messina, Italy; Catholic Univ, Rome, Italy; Brigham & Women's Hospital, HMS, Boston, MA
Background: B-RafV600E is the most common genetic alteration in papillary thyroid cancer (PTC), especially in aggressive subtypes such as tall cell PTC, and in those with extra-thyroidal extension. However, mechanisms by which B-RafV600E induce tumor aggressiveness are still not fully understood. Thrombospondin (TSP-1) is a multifunctional extracellular protein that has been positively associated with tumor cell migration. We chose to look at whether B-RafV600E modulates TSP-1 in PTC, both in vitro and in vivo.
Design: We applied Gene Set Enrichment Analysis (GSEA) to gene microarray data from 26 PTCs-RafV600E, 14 PTCs-wild type (wt) Braf, and 10 normal thyroid (NT) tissue samples to look at significantly altered genes (leading edge). Short hairpin RNAs were used to knock-down (KD) wtBraf and BrafV600E mRNA.
Results: The leading edge of gene sets significantly associated to B-RafV600E PTCs included several adhesion molecules, such as TSP-1, which is a member of the Breast Cancer Signaling gene set (BCS). Validation for TSP-1 was performed by immunostaining in tissue microarrays (TMAs) of a cohort of thyroid tissue samples including PTC-RafV600E, PTC wtBraf and benign/NT samples. PTC-RafV600E showed higher tumoral TSP-1 expression levels, whereas benign/NT samples showed consistently lower levels. KD of B-RafV600E in an aggressive human PTC cell line 8505 (homozygous for B-RafV600E) resulted in TSP-1 mRNA and protein down-regulation, as well as in a reduction of cell migration/invasion. KD of TSP-1 in 8505 cells also resulted in a similar reduction in cell migration/invasion. Both B-RafV600E and TSP-1 KD vs control reduced cell proliferation. Conversely, wt Braf KD in the human PTC cell line TPC-1 (RET/PTC1 and wtBraf) did not affect TSP-1 mRNA and protein levels, and neither cellular proliferation nor migration/invasion.
Conclusions: B-RafV600E 's role in the aggressiveness of thyroid cancer may be linked to adhesion molecules in the BCS gene set, in particular TSP-1. Further studies with TSP-1 and other BCS genes should be performed to identify new therapeutic targets.
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 88, Monday Morning