Colorectal cancer (CRC) is one of the most common tumor entities, which is causally linked to DNA repair defects and inflammatory bowel disease (IBD). Here, we studied the role of the DNA repair protein poly(ADP-ribose) polymerase-1 (PARP-1) in CRC. Tissue microarray analysis revealed PARP-1 overexpression in human CRC, correlating with disease progression. To elucidate its function in CRC, PARP-1 deficient (PARP-1) and wild-type animals (WT) were subjected to azoxymethane (AOM)/ dextran sodium sulfate (DSS)-induced colorectal carcinogenesis. Miniendoscopy showed significantly more tumors in WT than in PARP-1 mice. Although the lack of PARP-1 moderately increased DNA damage, both genotypes exhibited comparable levels of AOM-induced autophagy and cell death. Interestingly, miniendoscopy revealed a higher AOM/DSS-triggered intestinal inflammation in WT animals, which was associated with increased levels of innate immune cells and proinflammatory cytokines. Tumors in WT animals were more aggressive, showing higher levels of STAT3 activation and cyclin D1 up-regulation. PARP-1 animals were then crossed with -methylguanine-DNA methyltransferase (MGMT)-deficient animals hypersensitive to AOM. Intriguingly, PARP-1/MGMT double knockout (DKO) mice developed more, but much smaller tumors than MGMT animals. In contrast to MGMT-deficient mice, DKO animals showed strongly reduced AOM-dependent colonic cell death despite similar -methylguanine levels. Studies with PARP-1 cells provided evidence for increased alkylation-induced DNA strand break formation when MGMT was inhibited, suggesting a role of PARP-1 in the response to -methylguanine adducts. Our findings reveal PARP-1 as a double-edged sword in colorectal carcinogenesis, which suppresses tumor initiation following DNA alkylation in a MGMT-dependent manner, but promotes inflammation-driven tumor progression.

TRPV4 is a cell surface-expressed calcium-permeable cation channel that mediates cell-specific effects on cellular morphology and function. Dominant missense mutations of TRPV4 cause distinct, tissue-specific diseases, but the pathogenic mechanisms are unknown. Mutations causing peripheral neuropathy localize to the intracellular N-terminal domain whereas skeletal dysplasia mutations are in multiple domains. Using an unbiased screen, we identified the cytoskeletal remodeling GTPase RhoA as a TRPV4 interactor. TRPV4-RhoA binding occurs via the TRPV4 N-terminal domain, resulting in suppression of TRPV4 channel activity, inhibition of RhoA activation, and extension of neurites in vitro. Neuropathy but not skeletal dysplasia mutations disrupt TRPV4-RhoA binding and cytoskeletal outgrowth. However, inhibition of RhoA restores neurite length in vitro and in a fly model of TRPV4 neuropathy. Together these results identify RhoA as a critical mediator of TRPV4-induced cell structure changes and suggest that disruption of TRPV4-RhoA binding may contribute to tissue-specific toxicity of TRPV4 neuropathy mutations.

Summary Transient Receptor Potential (TRP) channels are polymodally regulated ion channels. TRPV4 (vanilloid 4) is sensitized by PIP2 and desensitized by Syndapin3/PACSIN3 which bind to the structurally uncharacterized TRPV4 N-terminus. We determined the NMR structure of the Syndapin3/PACSIN3 SH3 domain in complex with the TRPV4 N-terminal proline rich region (PRR), which binds as a class I poly-proline II (PPII) helix. This PPII conformation is broken by a conserved proline in a cis conformation. Beyond the PPII, we find that the proximal TRPV4 N-terminus is unstructured, a feature conserved across species thus explaining the difficulties in resolving it in previous structural studies. Syndapin/PACSIN SH3 domain binding leads to rigidification of both the PRR and the adjacent PIP2-binding site. We determined the affinities of the TRPV4 N-terminus for PACSIN1, 2 and 3 SH3 domains and PIP2 and deduce a hierarchical interaction network where Syndapin/PACSIN binding influences the PIP2-binding site but not vice versa.

Rhodesain is a major cysteine protease of Trypanosoma brucei rhodesiense, a pathogen causing Human African Trypanosomiasis, and a validated drug target. Recently, we reported the development of α-halovinylsulfones as a new class of covalent reversible cysteine protease inhibitors. Here, αfluorovinylsulfones/-sulfonates were optimized for rhodesain based on molecular modeling approaches. 2d, the most potent and selective inhibitor in the series, shows a single-digit nanomolar affinity and high selectivity toward mammalian cathepsins B and L. Enzymatic dilution assays and MS experiments indicate that 2d is a slow-tight binder (K i = 3 nM). Furthermore, the nonfluorinated 2d-(H) shows favorable metabolism and biodistribution by accumulation in mice brain tissue after intraperitoneal and oral administration. The highest antitrypanosomal activity was observed for inhibitors with an N-terminal 2,3-dihydrobenzo [b][1,4]dioxine group and a 4-Me-Phe residue in P2 (2e/4e) with nanomolar EC 50 values (0.14/0.80 μM). The different mechanisms of reversible and irreversible inhibitors were explained using QM/MM calculations and MD simulations.