Review The Expanded Human Kallikrein (KLK) Gene Family: Genomic Organisation, Tissue-Specific Expression and Potential Functions

conserved structurally, their known or predicted enzymic functions are specific and distinct from one another. They also share a wide range of expression patterns that likely indicate involvement in a diverse range of physiological processes (Bhoola et al., 1992; Clements, 1997; Ritten-house et al., 1998; Diamandis et al., 2000). In contrast to the rodent tissue kallikrein (KLK) gene families, the human KLK gene family appeared to consist of just three genes – KLK1 encoding tissue kallikrein, KLK2 encoding glandular kallikrein and KLK3, which en-codes prostate-specific antigen or PSA (Riegman et al., 1992; Clements, 1994). These enzymes play important roles in the (patho)physiology of the kidney, pancreas and brain and cardiovascular, respiratory, gastrointestinal and reproductive systems (tissue kallikrein), prostate (PSA and K2) and breast (PSA) (Bhoola et al., 1992; Clements, 1997; Rittenhouse et al., 1998; Black and Diamandis, 2000). Recently, several groups have identified other hu