MUC5AC and colorectal cancer: Byrd et al. reviewed all mucins and mucin-binding proteins in colorectal cancer and suggested that the MUC2 gene and MUC5AC gene were expressed simultaneously in mucus secreting cells during carcinogenesis, which may be due to the common regulatory mechanism, namely, pKa, PKC, PKG, Ca2, and SP1/SP3 signal transduction) (Byrd and Bresalier, 2004).