Anyone know ,Oncogenes supresses cancer or responsible for cancer?
its a gene that when mutated can be responsible for turning a normal cell into a cancerous one...In other word...these are suseptibility genes...presence and expression of a mutated form causes cancer...
I would disagree that an oncogene is 'mutated' in the development of cancer. On the contrary, oncogenes are generally activated or over-expressed in cancers. Not very many mutations can actually activate a protein, so mutations are more often found in tumour suppressor genes.
By the strict definition of an oncogene, an oncogene is a gene that when activated can contribute to the development of cancer. The prevailing theory behind the development of cancer these days is that it is caused by multiple events, not just the alteration of a single gene. This "activation" typically refers to an increase in expression of a so called proto-oncogene. A proto-oncogene is a gene that is acting normally in a cell until it is "activated" and becomes an oncogene. A cell that with a proto-oncogene that undergoes the necessary activation to become an oncogene is said to have been "transformed". Note the distinction between a transformed cell and a cancerous cell. While a transformed cell may lose its control over mitosis, it does not necessarily become cancerous.
As for mutations, it is typically believe that mutations lead to cancer, and in some cases that is the case. Note that when cells lose mitotic control, they start to divide a lot more than normal. When this happens mutations tend to accumulate a lot more than usual and thus may lead to cancer. Furthermore, a mutation in a gene's promoter may cause an increase in that gene's expression, which could lead to the activation of an oncogene. There is also evidence (although I can't remember an example right now) that a virus may integrate next to a proto-oncogene and under the right conditions increase its expression leading to the activation of the oncogene.
Those are good examples. Another mode of activation that should be added for completeness is chromosomal rearrangements such as translocations. This can either result in an enhancer from one gene driving the expression of an oncogene (e.g. the translocation of BCL2 near the IGH enhancer) or the generation of an oncogenic fusion transcript resulting from the cotranscription of the two genes involved in the translocation (e.g. BCR-ABL in leukemia).
Thank you for the addition and for using one of my favorite re-arrangements: the Philadelphia chromosome. Indeed chromosomal re-arrangements are a significant source of oncogenic activation. They actually are one of the "scariest" ones from a geneticist perspective since they are so hard to identify using conventional techniques. It is becoming easier to detect them but even current technology has to scan tons of DNA sites in search of re-arrangements. Of course if you know what you are looking for it becomes easier :).
There are also many examples of normal embryonic genes that get switched back on by mistake later in life. Melanoma-associated antigen genes (MAGE) for example.
To add to all that have been correctly mentioned previously, i am sure everyone is aware of the epigenetics (DNA methylation and associated changes) in playing a role in gene activation and suppression. However i just wanted to add that Oncogenes can be activated by hypomethylation of CpG(s) in the vicinity of its promoter and Tumor suppressor genes can be turned off by hypermethylation. Global DNA hypomethylation and hypermethylation of gene promoter specifc CpGs are important epigenetic finding in some cancers.
Its proto oncogenes which upon undergoing the mutation turn into the active oncogenes.