Affinage

KLK2

Kallikrein-2 · UniProt P20151

Length
261 aa
Mass
28.7 kDa
Annotated
2026-06-10
21 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

KLK2 is a prostate-specific, androgen-regulated trypsin-like serine protease that participates in prostate biology and prostate cancer through proteolytic processing of multiple substrates (PMID:20058238, PMID:20180640, PMID:39106042). Its transcription is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus driving enhancer activation; consistent with this dependence, KLK2 expression is absent in AR-negative and neuroendocrine prostate cancer (PMID:42189191). Enzymatically, KLK2 cleaves preferentially after arginine residues, activating the PSA (KLK3) zymogen (PMID:20058238), degrading IGFBP-3 into small fragments (PMID:20180640), and cleaving the extracellular domain of macrophage IL-10 receptor chain-2 (IL-10R2) at the SYRIF sequence to reduce IL-10R2 surface levels and blunt IL-10-mediated anti-inflammatory signaling, an activity favored at pH 8.0–8.2 and enhanced by sodium citrate and glycosaminoglycans (PMID:39106042). Beyond proteolysis, KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance AR transactivation, with knockdown causing apoptosis and G1 arrest (PMID:24122203). An oncogenic KLK2-FGFR2 fusion identified in metastatic disease constitutively activates FGFR signaling and is sensitive to selective FGFR inhibitors (PMID:31043681). Its enzymatic activity can be specifically blocked by cyclized inhibitory peptides developed for in vivo application (PMID:18627344).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2002 Medium

    Established that the KLK2 locus generates more than the canonical protease, revealing an alternatively spliced, androgen-regulated transcript encoding a distinct prostate-specific protein.

    Evidence Molecular cloning of splice-variant mRNAs and androgen-stimulation expression analysis

    PMID:11834722

    Open questions at the time
    • Functional role of the K-LM protein not established
    • No protein-level activity or partner identified
  2. 2008 Medium

    Showed that KLK2 proteolytic activity is specifically druggable, providing chemical tools to dissect and inhibit its function in vivo.

    Evidence In vitro enzymatic activity assays with cyclized inhibitory peptides

    PMID:18627344

    Open questions at the time
    • Abstract-level detail only
    • In vivo efficacy not demonstrated in this work
    • Substrate specificity of inhibition not defined
  3. 2010 High

    Resolved which protease activates the PSA zymogen by demonstrating KLK2-mediated PSA activation across orthogonal models, defining a key step in prostate kallikrein cascades.

    Evidence Cell co-incubation, xenograft co-inoculation, and PSA/KLK2 double-transgenic mice measuring free/total PSA

    PMID:20058238

    Open questions at the time
    • Physiological/pathological consequence of PSA activation not addressed
    • Cleavage kinetics versus other activators not compared
  4. 2010 High

    Defined a substrate relevant to growth-factor signaling by mapping KLK2 cleavage of IGFBP-3, consistent with its trypsin-like Arg-directed specificity.

    Evidence In vitro proteolysis with immunoblot, native/total immunoassays, mass-spec site mapping, and peptide-inhibitor dose response

    PMID:20180640

    Open questions at the time
    • Downstream effect on IGF signaling not directly demonstrated
    • Cellular relevance versus in vitro proteolysis not established
  5. 2014 Medium

    Linked KLK2 to prostate cancer cell proliferation through a non-proteolytic transcriptional mechanism, showing it enhances AR transactivation via ARA70.

    Evidence KLK2 cDNA overexpression and siRNA knockdown in LNCaP, colony formation, xenograft growth, and AR transactivation reporter assays

    PMID:24122203

    Open questions at the time
    • Single lab
    • Mechanism of ARA70/AR cooperation not structurally defined
    • Whether proteolytic activity contributes to growth effect unclear
  6. 2019 Medium

    Identified an oncogenic KLK2-FGFR2 gene fusion as a driver event, connecting the androgen-driven locus to constitutive growth-factor receptor signaling.

    Evidence Targeted RNA-seq fusion discovery, retroviral expression in NIH3T3, migration/signaling assays, FGFR inhibitor sensitivity panel

    PMID:31043681

    Open questions at the time
    • Frequency in patient populations not established
    • Functional studies in patient-derived prostate models lacking
    • Role of KLK2 portion in fusion activity undefined
  7. 2024 High

    Uncovered an immunomodulatory function by showing KLK2 cleaves IL-10R2 on macrophages to dampen anti-inflammatory signaling, with biochemical optima and a KLK3 negative control.

    Evidence FRET peptide-library substrate screen, FACS for IL-10R2 surface expression on BMDMs, inflammatory readouts (NO, TNF-alpha, IL-12 p40)

    PMID:39106042

    Open questions at the time
    • In vivo relevance in the tumor microenvironment not shown
    • Source of KLK2 acting on macrophages not defined
    • Single lab
  8. 2026 Medium

    Mechanistically anchored KLK2 expression to AR/FOXA1/HOXB13 enhancer co-regulation across large mCRPC cohorts and showed loss in AR-negative/neuroendocrine disease.

    Evidence Transcriptomic/epigenomic profiling (ChIP/ATAC-seq) of 1095 mCRPC samples plus rapid autopsy in situ studies

    PMID:42189191

    Open questions at the time
    • Correlative multi-omics rather than direct locus manipulation
    • Causality of individual factor binding not tested functionally

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether KLK2 cell-surface localization is a robust, generalizable feature enabling therapeutic targeting remains to be established with direct experimental detail.
  • Experimental details of surface localization not in the cited commentary
  • Mechanism of membrane association of a secreted protease unknown
  • Targetability claim not independently validated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016787 hydrolase activity 3 GO:0140096 catalytic activity, acting on a protein 3 GO:0098772 molecular function regulator activity 1
Localization
GO:0005576 extracellular region 2
Pathway
GO:0140110 transcription regulator activity 2

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 KLK2 is the protease responsible for activating PSA (KLK3) zymogen, demonstrated in cell-based in vitro models (co-incubated cell clones), in vivo xenograft co-inoculation experiments, and PSA/KLK2 double-transgenic mice where double-transgenic animals produced more active PSA than single-transgenic animals. Cell-based co-incubation assays, subcutaneous xenograft co-inoculation, and prostate-targeted double-transgenic mouse models measuring free/total PSA ratios The Prostate High 20058238
2010 KLK2 degrades IGFBP-3 into multiple small fragments with cleavage preferentially after Arg residues, consistent with its trypsin-like serine protease activity; cleavage sites were identified by mass spectrometry, and fragmentation was inhibited by KLK2-inhibiting peptides in a dose-dependent fashion. In vitro proteolysis assay with immunoblotting, two specific immunoassays (native vs. total IGFBP-3), mass spectrometry identification of cleavage sites, and KLK2-inhibiting peptide dose-response Biological chemistry High 20180640
2008 KLK2 enzymatic (proteolytic) activity can be specifically inhibited by peptides developed against it; peptide stability was improved by cyclization, enabling development of in vivo-applicable KLK2 inhibitors. Peptide-based enzymatic activity assays, in vitro peptide inhibition, peptide cyclization for stability improvement Biological chemistry Medium 18627344
2014 KLK2 promotes prostate cancer cell growth by cooperating with the AR coregulator ARA70 to enhance androgen receptor (AR) transactivation; KLK2 knockdown by siRNA caused increased apoptosis and G1-phase cell growth arrest, while KLK2 cDNA addition increased cell growth. KLK2 cDNA overexpression, KLK2-siRNA knockdown in LNCaP cells, colony formation assay, in vivo xenograft growth assay, AR transactivation reporter assay Tumour biology Medium 24122203
2019 A KLK2-FGFR2 fusion protein (identified in metastatic prostate cancer) activates downstream FGFR signaling pathways, promotes enhanced cell migration, and induces profound morphological changes when expressed in NIH3T3 cells; the fusion is sensitive to selective FGFR inhibitors (AZD-4547, BGJ398, JNJ-42756943, TAS-120, Ponatinib) but not Dovitinib. Targeted RNA-sequencing to identify fusion, retroviral transduction of NIH3T3 cells, migration assays, Western blots for downstream FGFR signaling activation, drug sensitivity assays Prostate cancer and prostatic diseases Medium 31043681
2024 KLK2 cleaves the extracellular domain of IL-10 receptor chain-2 (IL-10R2) at the sequence SYRIF (residues 58–63), reducing IL-10R2 surface expression on macrophages and blunting IL-10-mediated anti-inflammatory signaling (decreased inhibition of nitric oxide, TNF-α, and IL-12 p40). KLK2 is fully active at pH 8.0–8.2 and is strongly activated by sodium citrate and glycosaminoglycans. KLK3 did not show the same effects. FRET peptide library screening to identify optimal substrate (SYRIF), flow cytometry (FACS) to measure IL-10R2 surface expression on bone-marrow-derived macrophages after KLK2 treatment, functional inflammatory assays measuring nitric oxide, TNF-α, and IL-12 p40; comparison with KLK3 Biochemistry High 39106042
2025 KLK2, previously considered a purely secreted serine protease with no cell-surface localization, has now been demonstrated to be expressed on the cell surface, making it targetable by antibody-based and other therapeutic modalities. Experimental demonstration of cell-surface localization (details attributed to a related article by Shen et al.) Clinical cancer research Low 40924642
2026 KLK2 expression is strictly dependent on androgen receptor (AR) signaling, with coordinated binding of AR, FOXA1, and HOXB13 at the KLK2 locus and associated enhancer activation, as determined by epigenomic analysis of mCRPC patient samples; KLK2 expression is absent in neuroendocrine and AR-negative prostate cancer phenotypes. Transcriptomic and epigenomic profiling of 1095 mCRPC patient samples including ChIP/ATAC-seq-based analysis of AR/FOXA1/HOXB13 binding and enhancer activation, rapid autopsy cohort in situ studies Molecular cancer research Medium 42189191
2002 Alternative splicing of KLK2 involving inclusion of intronic sequences adjacent to exon 1 produces a novel protein (hK2-linked molecule, K-LM) that shares only the signal peptide with KLK2; the mature K-LM protein is entirely different from kallikreins and shows androgen-regulated prostate-specific expression similar to KLK2. Identification of splice variant mRNAs by molecular cloning, protein characterization, and androgen-stimulation expression analysis The Journal of biological chemistry Medium 11834722

Source papers

Stage 0 corpus · 21 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Unusual alternative splicing within the human kallikrein genes KLK2 and KLK3 gives rise to novel prostate-specific proteins. The Journal of biological chemistry 50 11834722
2014 Human kallikrein 2 (KLK2) promotes prostate cancer cell growth via function as a modulator to promote the ARA70-enhanced androgen receptor transactivation. Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine 48 24122203
2010 Prostate-specific antigen (PSA) is activated by KLK2 in prostate cancer ex vivo models and in prostate-targeted PSA/KLK2 double transgenic mice. The Prostate 33 20058238
2014 Loss of miR-378 in prostate cancer, a common regulator of KLK2 and KLK4, correlates with aggressive disease phenotype and predicts the short-term relapse of the patients. Biological chemistry 31 25153390
2006 Variants of the hK2 protein gene (KLK2) are associated with serum hK2 levels and predict the presence of prostate cancer at biopsy. Clinical cancer research : an official journal of the American Association for Cancer Research 30 17085659
2009 A comprehensive resequence analysis of the KLK15-KLK3-KLK2 locus on chromosome 19q13.33. Human genetics 25 19823874
2008 Development of peptides specifically modulating the activity of KLK2 and KLK3. Biological chemistry 24 18627344
2013 Genetic variation in KLK2 and KLK3 is associated with concentrations of hK2 and PSA in serum and seminal plasma in young men. Clinical chemistry 21 24270797
2018 Discovery of novel transcripts of the human tissue kallikrein (KLK1) and kallikrein-related peptidase 2 (KLK2) in human cancer cells, exploiting Next-Generation Sequencing technology. Genomics 15 29614347
2012 Birth-and-death of KLK3 and KLK2 in primates: evolution driven by reproductive biology. Genome biology and evolution 13 23204305
2024 Genomic and Immunologic Correlates in Prostate Cancer with High Expression of KLK2. International journal of molecular sciences 11 38396898
2010 Identification of IGFBP-3 fragments generated by KLK2 and prevention of fragmentation by KLK2-inhibiting peptides. Biological chemistry 11 20180640
2013 Genome-wide association study identifies loci at ATF7IP and KLK2 associated with percentage of circulating free PSA. Neoplasia (New York, N.Y.) 10 23359319
2019 Characterization of a KLK2-FGFR2 fusion gene in two cases of metastatic prostate cancer. Prostate cancer and prostatic diseases 7 31043681
2017 Trichosanthes kirilowii Exerts Androgenic Activity via Regulation of PSA and KLK2 in 22Rv1 Prostate Cancer Cells. Pharmacognosy magazine 3 28216900
2013 Association of Polymorphism rs198977 in Human Kallikrein-2 Gene (KLK2) with Susceptibility of Prostate Cancer: A Meta-Analysis. PloS one 2 23824286
2025 Drug Targets in Prostate Cancer: An Appetite for KLK2-Mediated Destruction. Clinical cancer research : an official journal of the American Association for Cancer Research 1 40924642
2024 Extracellular Domain of IL-10 Receptor Chain-2 (IL-10R2) and Its Arginine-Containing Peptides Are Susceptible Substrates for Human Prostate Kallikrein-2 (KLK2). Biochemistry 1 39106042
2023 KLK2 single-nucleotide polymorphism rs198977 is associated with increased susceptibility and hyperleukocytosis in AML. Frontiers in genetics 1 37593117
2026 Molecular Characterization of KLK2 RNA Expression in Prostate Cancer. Clinical cancer research : an official journal of the American Association for Cancer Research 0 41817312
2026 Integrative Surface Antigen Profiling of KLK2 and STEAP1 in Advanced Prostate Cancer. Molecular cancer research : MCR 0 42189191

Missed literature

Know a paper Affinage missed for KLK2? Flag it for the maintainers and the community.

No submissions yet.