N‐ras protein: Frequent quantitative and qualitative changes occur in human colorectal carcinomas

• Published in: International journal of cancer 1997-05, Vol.71 (5), p.767-775
• Main Authors: Kim, Kwonseop, Kuo, Tom, Cai, Jinguo, Shuja, Sania, Murnane, Mary Jo
• Format: Article
• Language: English
• Subjects: Antibodies, Monoclonal; Biological and medical sciences; Blotting, Western; Colorectal Neoplasms - metabolism; Gastroenterology. Liver. Pancreas. Abdomen; Gene Expression; Genes, ras - genetics; Humans; Intestinal Mucosa - metabolism; Medical sciences; Point Mutation; ras Proteins - analysis; ras Proteins - metabolism; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; Tumors
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/(SICI)1097-0215(19970529)71:5<767::AID-IJC13>3.0.CO;2-5

Point mutation and overexpression are recognized mechanisms for ras activation in malignancy. However, little information is available on overexpression of N‐ras protein compared with H‐ or K‐ras proteins, as N‐ras‐specific antibodies have only recently become available. For comparative analyses of ras protein levels, we have probed Western blots of extracts from 9 normal human tissues and 55 pairs of colorectal carcinoma and matched control mucosa, using monoclonal antibodies (MAbs) specific for H‐, K‐ or N‐ras proteins. On multi‐tissue blots, N‐ras protein was more highly expressed in colon than in the other human tissues analyzed, suggesting a role for N‐ras in colorectal function. N‐ras protein levels in multiple independent extracts of normal colon mucosa were consistently higher than either K‐ras protein or H‐ras protein levels. In 69% of colon carcinomas, N‐ras protein levels were increased an average of 4.8‐fold over normal mucosa. Overexpression of K‐ras protein was also observed in colon cancers but less frequently (13% of cases) than N‐ras protein. H‐ras protein levels were too low for comparative studies. Alterations in N‐ras protein mobility, possibly reflecting increased post‐translational processing, were also detected in 42% of colon carcinomas. N‐ras protein, typically present as a single 23 kDa band in normal mucosa, was expressed in some cancers as a 22 kDa band or as multiple bands of 20‐23 kDa. Sequencing of N‐ras DNA from 6 carcinomas with these variations in protein mobility did not reveal mutations in codons 12, 13, 59 or 61. Thus, frequent quantitative and qualitative changes in N‐ras protein expression, which do not appear to correlate with the presence of typical N‐ras point mutations, result in abnormal N‐ras protein patterns in human colorectal carcinomas. Int. J. Cancer 71: 767‐775, 1997. © 1997 Wiley‐Liss Inc.