RbAp48 is a target of nuclear factor-kappaB activity in thyroid cancer.
BACKGROUND
We have recently shown that nuclear factor (NF)-kappaB activity is constitutively elevated in anaplastic human thyroid carcinomas. The inhibition of NF-kappaB in the anaplastic thyroid carcinoma cell line (FRO) leads to increased susceptibility to apoptosis induced by chemotherapeutic drugs and to the block of oncogenic activity.


OBJECTIVE
To understand better the molecular mechanisms played by NF-kappaB in thyroid oncogenesis, we performed a differential proteomic analysis between FRO transfected with a superrepressor form of inhibitor of kappaBalpha (IkappaBalphaM) and the parental counterpart (FRO Neo cells).


RESULTS
Differential proteomic analysis revealed that the retinoblastoma-associated protein 48 (RbAp48) is down-regulated in the absence of functional NF-kappaB. Immunohistochemical analysis of normal and pathological human thyroid specimens confirmed that RbAp48 is strongly overexpressed in primary human carcinomas. Reduction of RbAp48 expression using small interfering RNA determined the suppression of tumorigenicity, very likely due to the decrease of their growth rate rather than to an increased susceptibility to apoptosis. In addition, we showed that NF-kappaB, at least in part, transcriptionally controls RbAp 48. A functional NF-kappaB consensus sequence was located within the promoter region of RbAp48 human gene, and embryonic fibroblasts isolated from the p65 knockout mouse (murine embryonic fibroblasts p65-/-) showed decreased expression of RbAp48.


CONCLUSIONS
Our results show that RbAp48 is a NF-kappaB-regulated gene playing an important role in thyroid cancer cell autonomous proliferation.
Pacifico
Francesco
F
Istituto di Endocrinologia e Oncologia Sperimentale, Consiglio Nazionale delle Richerche, Naples, Italy.
Paolillo
Michele
M
Chiappetta
Gennaro
G
Crescenzi
Elvira
E
Arena
Simona
S
Scaloni
Andrea
A
Monaco
Mario
M
Vascotto
Carlo
C
Tell
Gianluca
G
Formisano
Silvestro
S
Leonardi
Antonio
A
D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics*; D016384:Consensus Sequence; D004273:DNA, Neoplasm / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D013058:Mass Spectrometry; D016328:NF-kappa B / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D056505:Retinoblastoma-Binding Protein 4; D013936:Thymidine / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000378:metabolism*
D002352:Carrier Proteins; D004273:DNA, Neoplasm; D016328:NF-kappa B; D009687:Nuclear Proteins; C082637:RBBP4 protein, human; D034741:RNA, Small Interfering; D056505:Retinoblastoma-Binding Protein 4; D013936:Thymidine