CTSV

CTSV (cathepsin V/CTSL2) is a cysteine protease that acts both as an executioner of apoptosis and a driver of cancer cell proliferation, integrating transcriptional inputs from oncogenic signaling pathways (PMID:23542171, PMID:35443863). It is a direct transcriptional target of E2F1, which binds the CTSL2 promoter and requires CTSV to execute apoptosis through lysosomal membrane permeabilization and downstream mitochondrial membrane depolarization; CTSV is likewise required for DNA-damage- and HDAC-inhibitor-induced apoptosis, and its overexpression sensitizes cells to HDAC inhibitors (PMID:23542171). In a proliferative context, CTSV drives bladder cancer cell growth and xenograft tumor formation through activation of NF-κB transcriptional activity (PMID:35443863). CTSV expression is controlled by upstream oncogenic signaling: an EGFR-MEK-ERK axis upregulates CTSV to promote renal carcinoma migration and invasion (PMID:32331211), and a PKCα/PKCδ-ERK-Sp1 transcriptional axis governs CTSV expression and migratory behavior in colorectal cancer (PMID:40674912). Beyond these transcriptional and pathway-placement findings, the catalytic substrates and structural basis of CTSV protease activity have not been characterized in the available corpus.

1. 2013 High

   Established CTSV as a direct effector arm of E2F1-driven apoptosis, answering how a transcription factor couples to the lysosomal-mitochondrial death machinery.

   Evidence ChIP of E2F1 at the CTSL2 promoter plus RNAi loss-of-function and overexpression with apoptosis, LMP, and mitochondrial depolarization readouts in cancer cells

   PMID:23542171

   Open questions at the time

   • No protease substrate identified that links CTSV activity to LMP
   • Mechanism by which CTSV triggers lysosomal membrane permeabilization is not resolved
   • Single-lab; cell-line dependence of the apoptotic role untested broadly
2. 2020 Medium

   Placed CTSV downstream of EGFR-MEK-ERK signaling, identifying an upstream pathway that controls its expression and links it to invasion.

   Evidence EGF stimulation and pharmacological/pathway-specific inhibition with Western blot and RT-PCR in RCC cell lines, plus migration/invasion assays

   PMID:32331211

   Open questions at the time

   • Pathway placement rests on pharmacological inhibition; direct transcriptional mechanism not defined
   • Only two cell lines tested
   • Does not connect ERK regulation to the E2F1/apoptotic role
3. 2022 Medium

   Defined a downstream pro-proliferative output for CTSV via NF-κB activation, contrasting with its pro-apoptotic role and implicating it in tumor growth.

   Evidence Dual-luciferase NF-κB reporter with inhibitor rescue, siRNA/overexpression proliferation assays, and xenograft mouse model in bladder cancer

   PMID:35443863

   Open questions at the time

   • How CTSV protease activity activates NF-κB is not mechanistically defined
   • Pathway placement relies on a pharmacological NF-κB inhibitor
   • Reconciliation of pro-apoptotic vs pro-proliferative roles unaddressed
4. 2025 Medium

   Identified a PKCα/PKCδ-ERK-Sp1 transcriptional axis controlling CTSV expression and migration, extending upstream regulatory understanding into colorectal cancer.

   Evidence siRNA knockdown of ERK and CTSV, protease array, phospho-immunoblots, and TPA rescue with migration/invasion assays

   PMID:40674912

   Open questions at the time

   • Sp1 binding to the CTSV promoter inferred from activity, not direct binding assay here
   • Single-lab pharmacological/siRNA approach
   • Relationship to the EGFR-MEK-ERK axis not directly compared

• The endogenous catalytic substrates, structural basis, and subcellular site of CTSV protease action that mechanistically explain its apoptotic and pro-tumorigenic effects remain undefined.
• No CTSV proteolytic substrate identified in the corpus
• Mechanism linking protease activity to LMP and to NF-κB activation unknown
• No structural or enzymatic characterization in the timeline