MOLECULAR ONCOLOGY 1 (2007) 269–287 available at www.sciencedirect.com www.elsevier.com/locate/molonc Review New insights into the functional mechanisms and clinical applications of the kallikrein-related peptidase family Nashmil Emamia,b, Eleftherios P. Diamandisa,b,* aDepartment of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5G 1L5, Canada bDepartment of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada ABSTRACT ARTICLE INFO Article history: The Kallikrein-related peptidase (KLK) family consists of fifteen conserved serine proteases Received 13 July 2007 that form the largest contiguous cluster of proteases in the human genome. While primar- Received in revised form ily recognized for their clinical utilities as potential disease biomarkers, new compelling 4 September 2007 evidence suggests that this family plays a significant role in various physiological pro- Accepted 7 September 2007 cesses, including skin desquamation, semen liquefaction, neural plasticity, and body fluid Available online 15 September 2007 homeostasis. KLK activation is believed to be mediated through highly organized proteo- lytic cascades, regulated through a series of feedback loops, inhibitors, auto-degradation Keywords: and internal cleavages. Gene expression is mainly hormone-dependent, even though tran- Kallikrein-related peptidases scriptional epigenetic regulation has also been reported. These regulatory mechanisms are PSA integrated with various signaling pathways to mediate multiple functions. Dysregulation of Proteolytic cascades these pathways has been implicated in a large number of neoplastic and non-neoplastic Skin desquamation pathological conditions. This review highlights our current knowledge of structural/ * Corresponding author. Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario M5G 1X5, Canada. Tel.: þ1 416 586 8443; fax: þ1 416 619 5521. E-mail address: [email protected] (E.P. Diamandis). Abbreviations: ACC, 7-amino-4-carbamoylmethylcoumarin; ACT, anti-chymotrypsin; AD, Alzheimer’s disease; ADAMTS8, ADAM met- allopeptidase with thrombospondin type 1 motif 8; ANF, atrial natriuretic factor; AI, amelogenesis imperfecta; AP, anti plasmin; APMSF, 4-amidino-phenyl-methane-sulfonyl fluoride; AT, antitrypsin; bFGF, basic fibroblast growth factor; B2R, human bradykinin B2 receptor; CAG, cancer-associated gene; cdk, cyclin-dependent kinase 7; CDSN, corneodesmosin; CNS, central nervous system; DSC, desmocollin; DSG, desmoglein; ECM, extracellular matrix; FN, fibronectin; FTD, frontotemporal dementia; FRET, fluorescence resonance energy trans- fer; HEK, human embryonic kidney; hCAP, human cathelicidin; hGH, human growth hormone; HRE, hormone response element; hsp, heat shock protein; IGF, insulin-like growth factor; IGFBP, IGF binding protein; IFN, interferon; IL, interleukin; KD, kallidin; KLK, kalli- krein-related peptidase; KNRK, Kirsten virus-transformed normal rat kidney; LEKTI, lympho-epithelial Kazal-type inhibitor; LLP, low density lipoprotein; LK, low molecular weight kininogen; LMW, low molecular weight; LTP, long-term potentiation; MAPK, mitogen- activated protein kinase; MBP, myelin basic protein; MMP, matrix metalloproteinase; NS, Netherton syndrome; OLG, oligodendrocyte; PAI, plasminogen activator inhibitor; PAP, poly A polymerase; PAR, protease activated receptor; PCI, protein C inhibitor; PI, protease in- hibitor; PKA, protein kinase A; PKC, protein kinase C; PS-SCL, positional scanning synthetic combinatorial library; PTHrp, parathyroid hormone-related peptide; SC, stratum corneum; Sg, seminogelin; siRNA, small interfering RNA; SLPI, secretory leukocyte protease inhib- itor; SNP, single nucleotide polymorphism; SPINK, serine protease inhibitor Kazal-1; TGF, tumour growth factor; uPA, urokinase plas- minogen activator; uPAR, urokinase plasminogen activator receptor; UTR, untranslated region; VEGF, vascular endothelial growth factor; VIP, vasoactive intestinal peptide. 1574-7891/$ – see front matter ª 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.molonc.2007.09.003 270 MOLECULAR ONCOLOGY 1 (2007) 269–287 Semen liquefaction phylogenetic features, functional role and regulatory/signaling mechanisms of this impor- Tumour growth tant family of enzymes. Tumour invasion ª 2007 Federation of European Biochemical Societies. Angiogenesis Published by Elsevier B.V. All rights reserved. uPA signaling PARs 1. Introduction the genes. Some of the common features shared among KLKs include exon/intron organization, number and length Proteases (also known as peptidases) are a major group of en- of exonic regions, intron phase, and conserved translational zymes participating in multitude of physiological processes, start and stop sites, as well as the catalytic triad codons including coagulation, apoptosis, tissue remodeling, and im- (Borgono et al., 2004; Yousef and Diamandis, 2001). Each mune responses (Barrett et al., 2004). Depending on the cleav- geneconsistsof5codingexons,separatedby4introns age site, proteases are classified as exo- and endo-peptidases with the highly conserved GT-AG splice junction pattern. (Barrett et al., 2004). Endopeptidases (or proteinases) cleave Furthermore, with the exception of the ‘‘classic’’ KLKsthat their target proteins internally, whereas exopeptidases se- lack 50 untranslated exons, KLKs contain both 50 and 30 quentially remove amino acids from either the N or C-termi- UTRs. The 30 UTR contains either the canonical (AATAAA) nus (Barrett et al., 2004). Based on the amino acid residue or a variant polyadenylation site distal to the stop codon present at the active site, endopeptidases can further be (Fig. 1)(Borgono et al., 2004). grouped into four major classes of serine-, cysteine-, KLK proteins are secreted serine endoproteases, expressed aspartic-, and metallo-proteinases (Barrett et al., 2004). as single chain preproenzymes of approximately 30–40 kDa Serine proteases exhibit diverse functions in digestion, co- (Fig. 1)(Obiezu and Diamandis, 2005). The signal (pre-) se- agulation, and cellular and humoral immunity (Rawlings and quence is 16–30 amino acids in length and is cleaved from Barrett, 1994). Based on their evolutionary relationships, ser- the N-terminus of the protein prior to secretion (Yousef and ine proteases can further be grouped into eleven clans (Raw- Diamandis, 2001). Enzyme activation may subsequently occur lings and Barrett, 1994). The trypsin/chymotrypsin-like (clan through limited proteolysis targeted to the peptide bond be- SA) enzymes are considered as the main clan in the subfamily tween basic and hydrophobic residues of the ‘‘pro’’- sequence of the serine proteases (Rawlings and Barrett, 1994). (Gomis-Ruth et al., 2002)(Table 1). Characteristic to serine pro- Kallikrein-related peptidases belong to a subgroup of teases, KLKs contain a catalytic serine residue at their active secreted serine proteases within the S1 family of clan SA site cleft. Along with the active serine, histidine and aspartic (Borgono et al., 2004). So far, fifteen members of the family acid residues of the catalytic triad, serve as a charge relay sys- (KLK1-15) have been identified, most of which have been tem (Obiezu and Diamandis, 2005; Gomis-Ruth et al., 2002). reported as potential prognostic and/or diagnostic tumour KLKs share a high level of amino acid identity in areas biomarkers. flanking the catalytic triad (Obiezu and Diamandis, 2005). The initial work in the kallikrein-related peptidase re- The overall sequence similarity, however, is estimated at search was devoted to the discovery and characterization of a lower level (40%–80%) with highest sequence similarity the three members of the family known as the ‘‘classic’’ kalli- between the ‘‘classic’’ KLKs (Obiezu and Diamandis, 2005). krein-related peptidases (KLK1, 2, and 3), during 1930s–1980s So far, the 3D structure of mature KLK1, KLK4, and both (Borgono et al., 2004). Subsequent work from our laboratory mature and pro-KLK6 have been determined by X-ray crystal- and others has eventually led to the characterization of twelve lography (Debela et al., 2006a; Laxmikanthan et al., 2005; Ber- novel members in the past decade. nett et al., 2002; Gomis-Ruth et al., 2002). As a subgroup of the According to the official nomenclature system recommen- trypsin/chymotrypsin-like serine proteases, these KLKs are ded by the Kallikrein subcommittee of HGNC (HUGO Nomen- folded into two hydrophobically interacting domains of six- clature Committee) in 2006, kallikrein-related peptidases are stranded b-barrels and an a-helix. The catalytic triad is located denoted as KLKs (Lundwall et al., 2006a). To distinguish be- at the interface between the two domains, as a shallow tween proteins and genes, proteins are written in standard depression on the frontal surface (Debela et al., 2006a; font, e.g. KLK2, while genes are in italics, e.g. KLK2. Gomis-Ruth et al., 2002; Bernett et al., 2002). KLK1 contains an additional ‘‘kallikrein loop’’, unique to the ‘‘classic’’ KLKs (Laxmikanthan et al., 2005). The loop consists of 11 amino 2. Gene organization and protein structure acids, inserted at position 95 (Laxmikanthan et al., 2005). Given its close proximity to the active site, the kallikrein KLKs are encoded by a cluster of strikingly similar genes loop is believed to affect the substrate accessibility of the en- with varying length, ranging from 4.4 to 10.5 kbp (Obiezu