Loss of Rap1GAP in papillary thyroid cancer.
BACKGROUND
Rap1 GTPase-activating protein (GAP) regulates the activity of Rap1, a putative oncogene. We previously reported Rap1GAP was highly expressed in normal human thyroid cells and decreased in five papillary thyroid carcinomas (PTCs).


OBJECTIVE
To confirm the significance of these findings, we analyzed Rap1GAP expression in a larger set of benign tumors (adenomas and hyperplastic nodules) and PTCs. We determined whether the presence of the BRAF(V600E) mutation or allelic loss of Rap1GAP related to changes in Rap1GAP protein expression. To determine the consequences of Rap1GAP loss, we targeted Rap1GAP in culture using small interfering RNA.


METHODS
A highly specific Rap1GAP antibody was applied to sections of 55 human thyroid tissues. Genomic DNA was analyzed for the presence of the BRAF(V600E) mutation, and loss of Rap1GAP. Rap1GAP expression in rat thyroid cells was abolished using small interfering RNA.


RESULTS
We observed that down-regulation of Rap1GAP in benign lesions and PTCs was common. Rap1GAP expression was more severely decreased in PTCs. Loss of Rap1GAP expression was observed in multiple histological variants of PTCs. Approximately 20% of PTCs and adenomas exhibited allelic loss of Rap1GAP. Loss of Rap1GAP was not associated with the presence of the BRAF(V600E) mutation. In vitro, loss of Rap1GAP was sufficient to increase Rap1 activity in thyroid cells.


CONCLUSIONS
These data indicate that loss of Rap1GAP is a frequent event in PTC. The more frequent and greater down-regulation of Rap1GAP in PTCs compared with adenomas suggests a role for Rap1GAP depletion in the progression of human thyroid tumors, possibly through unrestrained Rap activity.
Nellore
Anoma
A
Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Paziana
Karolina
K
Ma
Changqing
C
Tsygankova
Oxana M
OM
Wang
Yan
Y
Puttaswamy
Kanchan
K
Iqbal
Ammarah U
AU
Franks
Susanna R
SR
Lv
Yu
Y
Troxel
Andrea B
AB
Feldman
Michael D
MD
Meinkoth
Judy L
JL
Brose
Marcia S
MS
D002291:Carcinoma, Papillary / Q000737:chemistry* / Q000235:genetics / Q000473:pathology; D020690:GTPase-Activating Proteins / Q000032:analysis* / Q000502:physiology; D005838:Genotype; D006801:Humans; D007150:Immunohistochemistry; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000737:chemistry* / Q000235:genetics / Q000473:pathology
D020690:GTPase-Activating Proteins; C484658:RAP1GAP protein, human; D000089804:Shelterin Complex; C440809:TERF2IP protein, human; D034501:Telomere-Binding Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf