Osteopontin provides early proliferative drive and may be dependent upon aberrant c-myc signalling in murine intestinal tumours.
Osteopontin is thought to play an important role in tumour metastasis. In a previous expression profiling study of murine intestinal adenomas, we found that Opn was up-regulated. We also found beta-catenin binding motifs in the Opn promoter implying that, contrary to current beliefs, induction of Opn may occur during early tumourigenesis. We studied 59 murine intestinal adenomas for Opn expression and every tumour showed up-regulation compared to normal mucosa confirming early deregulation in these tumours. To determine whether Opn makes a functional contribution to tumourigenesis, Opn was knocked down in the murine colorectal cancer cell line CMT93. Inhibition of Opn expression resulted in decreased cell numbers. To determine the mechanism of Opn induction in these tumours, the Opn promoter was cloned and each of the putative beta-catenin binding motifs was mutated. No major change in Opn promoter activity was observed thereby excluding Opn as a direct beta-catenin target gene. However, mutation of one of two putative c-myc binding sites in the Opn promoter led to near complete loss of promoter activity whilst mutation of one of four PEA3 binding sites led to a 50% reduction in promoter activity. We conclude that Opn deregulation is an early event in intestinal tumourigenesis which may promote tumour development by altering either proliferation or apoptosis to increase tumour cell numbers. Opn expression in the intestine is dependent on c-myc binding sites in the promoter. Since c-myc is a known beta-catenin target gene, deregulation of Opn may be a secondary effect of aberrant Wnt signalling.
Martinez
Cristina
C
Digestive Diseases Research Unit, Institut Fundacio Recerca, Hospital General Vall D'hebron, 08035 Barcelona, Spain.
Churchman
Michael
M
Freeman
Tom
T
Ilyas
Mohammad
M
D000818:Animals; D002455:Cell Division / Q000502:physiology*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D003110:Colonic Neoplasms / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D015972:Gene Expression Regulation, Neoplastic; D007413:Intestinal Mucosa / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D053495:Osteopontin / Q000235:genetics* / Q000502:physiology; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D051176:beta Catenin / Q000502:physiology
D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin; D053495:Osteopontin; C495971:Hras protein, mouse; D016283:Proto-Oncogene Proteins p21(ras)