Identification of PTK6, via RNA sequencing analysis, as a suppressor of esophageal squamous cell carcinoma.
OBJECTIVE
Esophageal squamous cell carcinoma (ESCC) is the most commonly observed histologic subtype of esophageal cancer. ESCC is believed to develop via accumulation of numerous genetic alterations, including inactivation of tumor suppressor genes and activation of oncogenes. We searched for transcripts that were altered in human ESCC samples compared with nontumor tissues.


METHODS
We performed integrative transcriptome sequencing (RNA-Seq) analysis using ESCC samples from 3 patients and adjacent nontumor tissues to identify transcripts that were altered in ESCC tissue. We performed molecular and functional studies of the transcripts identified and investigated the mechanisms of alteration.


RESULTS
We identified protein tyrosine kinase 6 (PTK6) as a transcript that was significantly down-regulated in ESCC tissues and cell lines compared with nontumor tissues or immortalized normal esophageal cell lines. The promoter of the PTK6 gene was inactivated in ESCC tissues at least in part via hypermethylation and histone deacetylation. Knockdown of PTK6 in KYSE30 ESCC cells using small hairpin RNAs increased their ability to form foci, migrate, and invade extracellular matrix in culture and form tumors in nude mice. Overexpression of PTK6 in these cells reduced their proliferation in culture and tumor formation in mice. PTK6 reduced phosphorylation of Akt and glycogen synthase kinase (GSK)3β, leading to activation of β-catenin.


CONCLUSIONS
PTK6 was identified as a transcript that is down-regulated in human ESCC tissues via epigenetic modification at the PTK6 locus. Its product appears to regulate cell proliferation by reducing phosphorylation of Akt and GSK3β, leading to activation of β-catenin. Reduced levels of PTK6 promote growth of xenograft tumors in mice; it might be developed as a marker of ESCC.
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Stephanie
S
Ma
Genome Research Centre, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Jessie Y J
JYJ
Bao
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Pak Shing
PS
Kwan
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Yuen Piu
YP
Chan
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Carol M
CM
Tong
Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Li
L
Fu
Genome Research Centre, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Na
N
Zhang
Genome Research Centre, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Amy H Y
AHY
Tong
Department of Clinical Oncology, First Affiliated Hospital, Zhengzhou University, Zhengzhou, China.
Yan-Ru
YR
Qin
Department of Anatomy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Sai Wah
SW
Tsao
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Kwok Wah
KW
Chan
Genome Research Centre, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China. Electronic address: silok@genome.hku.hk.
Si
S
Lok
Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China. Electronic address: xyguan@hkucc.hku.hk.
Xin-Yuan
XY
Guan
D000107:Acetylation; D000328:Adult; D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D004938:Esophageal Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D059585:G1 Phase Cell Cycle Checkpoints; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D017423:Sequence Analysis, RNA; D015398:Signal Transduction; D014158:Transcription, Genetic; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism
C495270:CTNNB1 protein, human; D006657:Histones; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D051176:beta Catenin; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3