SMAD4 and inflammatory bowel disease: CRC - colorectal cancer; KRAS - Kirsten rat sarcoma virus; JNK - c-Jun N-terminal kinase; APC - adenomatous polyposis coli; SMAD4 - Mothers against decapentaplegic homolog 4; IBD - inflammatory bowel disease; HDL-C - high-density lipoprotein cholesterol; LDL-C - low-density lipoprotein cholesterol