Cancer-related genes can be classified into two major groups. Proto-oncogenes encode proteins that normally act in promoting cell growth and proliferation. Gain-of-function mutations in proto-oncogenes can therefore transform the cells into a cancerous state. Tumor suppressor genes, on the other hand, encode proteins that normally function to keep cell proliferation in check. Thus, loss-of-function mutations in tumor suppressors can lead to cancer by eliminating the inhibitory effect of these genes. Mutations in genes encoding the components of the canonical Wnt signaling pathway are commonly found in colorectal tumors. Indicate whether the gene for each of the following is a proto-oncogene (P) or tumor suppressor (T). Your answer would be a four-letter string composed of letters P and T only, e.g. PPPP.
( ) Wnt
( ) APC
( ) Axin
( ) ?-Catenin