Identification of a candidate tumor suppressor gene RHOBTB1 located at a novel allelic loss region 10q21 in head and neck cancer.
OBJECTIVE
Aims of the study are to narrow-down the hotspot region on 10q21 defined by previous genome-wide loss of heterozygosity (LOH) analysis in head and neck squamous cell carcinomas (HNSCC) and to define candidate tumor suppressor genes (TSG) concerned with 10q21.


METHODS
LOH analysis was carried out with ten polymorphic microsatellite markers. Expression analysis was performed by semi-quantitative RT-PCR, and mutation analysis by PCR and direct sequencing.


RESULTS
LOH analysis on 10q21 in 52 HNSCC indicated distinctive and frequent allelic loss at D10S589 (42%). Among flanking genes, we found the RHOBTB1 gene as a candidate TSG, since an intragenic marker demonstrated the highest LOH (44%). Expression analysis revealed down-regulation of RHOBTB1 mRNA in 37% of tumors. Interestingly, all the five tumors that showed decreased expression of RHOBTB1 were accompanied with LOH, supporting the haploinsufficiency and class 2 TSG characteristics of RHOBTB1. No pathogenic mutation of RHOBTB1 was found. Furthermore, another gene within the region, EGR2, was also taken under scope. LOH frequencies around the EGR2 gene were relatively low (23 and 33%). Albeit semi-quantitative expression analysis of EGR2 demonstrated downregulation in 45% of tumor samples, no relation was found between the expression levels and LOH status.


CONCLUSIONS
Frequent allelic loss and decreased expression of RHOBTB1 suggested that this gene has a role in tumorigenesis of a subset of HNSCC.
Beder
Levent B
LB
Department of Otolaryngology, Graduate School of Medicine and Dentistry, Okayama University, Okayama, Japan.
Gunduz
Mehmet
M
Ouchida
Mamoru
M
Gunduz
Esra
E
Sakai
Akiko
A
Fukushima
Kunihiro
K
Nagatsuka
Hitoshi
H
Ito
Sachio
S
Honjo
Noriyasu
N
Nishizaki
Kazunori
K
Shimizu
Kenji
K
D001483:Base Sequence; D002294:Carcinoma, Squamous Cell / Q000235:genetics*; D002879:Chromosomes, Human, Pair 10; D004252:DNA Mutational Analysis; D015536:Down-Regulation; D051767:Early Growth Response Protein 2 / Q000235:genetics*; D005091:Exons; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D005819:Genetic Markers; D006258:Head and Neck Neoplasms / Q000235:genetics*; D006801:Humans; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction
C497326:EGR2 protein, human; D051767:Early Growth Response Protein 2; D005819:Genetic Markers; D012333:RNA, Messenger