<prompt> All of the following are tumor suppressor genes except: September 200NF1pRbSMAD1p53  <response>: Ans. C: SMAD1Tumor suppressor geneanti-oncogene is a gene that protects a cell from one step on the path to cancer. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes.The first tumor-suppressor protein discovered was the Retinoblastoma protein pRbRB1 in human retinoblastoma. Another impoant tumor suppressor is the p53 tumor-suppressor protein encoded by the TP53 gene.Homozygous loss of p53 is found in 70 of colon cancers, 30-50 of breast cancers, and 50 of lung cancers. Mutated p53 is also involved in the pathophysiology of leukemias, lymphomas, sarcomas, and neurogenic tumors. Abnormalities of the p53 gene can be inherited in Li-Fraumeni syndrome LFS, which increases the risk of developing various types of cancers. PTEN acts by opposing the action of PI3K, which is essential for anti-apoptotic, pro-tumorogenic Akt activation.NFl somatic mutations is associated with neuroblastomas and neurofibromatosis type 1 is associated with inherited mutations of NFl.Other examples of tumor suppressors include APC, SMAD2, SMAD4 and ST14. 