Prohibitin is overexpressed in papillary thyroid carcinomas bearing the BRAF(V600E) mutation.
BACKGROUND
Prohibitin (PHB) is a multifunctional protein that is localized in different intracellular sites. PHB may exert different roles in tumorigenesis, having either a permissive action on tumor growth or an oncosuppressor role, depending on the cellular context. The objective of this study was to evaluate PHB expression in normal thyroid tissues, thyroid follicular adenomas (FAs), and papillary thyroid carcinomas (PTCs).


METHODS
PHB expression was analyzed by immunohistochemistry, Western blot, and quantitative reverse transcription polymerase chain reaction (RT-PCR). Transfections in the BCPAP and TPC-1 thyroid cancer cell lines were used to evaluate the PHB promoter activity.


RESULTS
In terms of protein and mRNA levels, normal tissues from patients with serum thyrotropin (TSH) values >0.8mU/L had PHB levels that were significantly reduced compared to specimens from patients with serum TSH values <0.5mU/L, suggesting that TSH exerts an inhibitory effect on PHB expression. Consistent with this was the finding that the presence of TSH was associated with low PHB levels in normal FRTL5 thyroid cells. Immunohistochemical analysis showed relatively low and high PHB expression in FAs and PTCs, respectively. PHB mRNA and protein overexpression, as assessed by quantitative RT-PCR and Western blot, was noted only in PTCs bearing the BRAF(V600E) mutation. Notably, cell transfection experiments suggested that presence of the BRAF(V600E) mutation may be associated to increase of the PHB promoter activity.


CONCLUSIONS
PHB is overexpressed in PTCs bearing the BRAF(V600E) mutation. We postulate that the presence of the BRAF(V600E) mutation increases PHB promoter activity and therefore potentially mediates effects of this mutation on the behavior of BRAF(V600E) positive PTCs.
Franzoni
Alessandra
A
Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, Udine, Italy.
Dima
Mariavittoria
M
D'Agostino
Maria
M
Puppin
Cinzia
C
Fabbro
Dora
D
Loreto
Carla Di
CD
Pandolfi
Maura
M
Puxeddu
Efisio
E
Moretti
Sonia
S
Celano
Marilena
M
Bruno
Rocco
R
Filetti
Sebastiano
S
Russo
Diego
D
Damante
Giuseppe
G
D000236:Adenoma / Q000378:metabolism; D000328:Adult; D015153:Blotting, Western; D002291:Carcinoma, Papillary / Q000378:metabolism*; D002460:Cell Line; D017931:DNA Primers; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics / Q000502:physiology*; D000091402:Prohibitins; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013961:Thyroid Gland / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000378:metabolism*; D013972:Thyrotropin / Q000096:biosynthesis
D017931:DNA Primers; C000717328:PHB protein, human; D000091402:Prohibitins; D012333:RNA, Messenger; D012097:Repressor Proteins; D013972:Thyrotropin; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf